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Diffstat (limited to 'src/backend/storage/lmgr/predicate.c')
| -rw-r--r-- | src/backend/storage/lmgr/predicate.c | 4439 |
1 files changed, 4439 insertions, 0 deletions
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c new file mode 100644 index 00000000000..5e62ba9e4d9 --- /dev/null +++ b/src/backend/storage/lmgr/predicate.c @@ -0,0 +1,4439 @@ +/*------------------------------------------------------------------------- + * + * predicate.c + * POSTGRES predicate locking + * to support full serializable transaction isolation + * + * + * The approach taken is to implement Serializable Snapshot Isolation (SSI) + * as initially described in this paper: + * + * Michael J. Cahill, Uwe Röhm, and Alan D. Fekete. 2008. + * Serializable isolation for snapshot databases. + * In SIGMOD ’08: Proceedings of the 2008 ACM SIGMOD + * international conference on Management of data, + * pages 729–738, New York, NY, USA. ACM. + * http://doi.acm.org/10.1145/1376616.1376690 + * + * and further elaborated in Cahill's doctoral thesis: + * + * Michael James Cahill. 2009. + * Serializable Isolation for Snapshot Databases. + * Sydney Digital Theses. + * University of Sydney, School of Information Technologies. + * http://hdl.handle.net/2123/5353 + * + * + * Predicate locks for Serializable Snapshot Isolation (SSI) are SIREAD + * locks, which are so different from normal locks that a distinct set of + * structures is required to handle them. They are needed to detect + * rw-conflicts when the read happens before the write. (When the write + * occurs first, the reading transaction can check for a conflict by + * examining the MVCC data.) + * + * (1) Besides tuples actually read, they must cover ranges of tuples + * which would have been read based on the predicate. This will + * require modelling the predicates through locks against database + * objects such as pages, index ranges, or entire tables. + * + * (2) They must be kept in RAM for quick access. Because of this, it + * isn't possible to always maintain tuple-level granularity -- when + * the space allocated to store these approaches exhaustion, a + * request for a lock may need to scan for situations where a single + * transaction holds many fine-grained locks which can be coalesced + * into a single coarser-grained lock. + * + * (3) They never block anything; they are more like flags than locks + * in that regard; although they refer to database objects and are + * used to identify rw-conflicts with normal write locks. + * + * (4) While they are associated with a transaction, they must survive + * a successful COMMIT of that transaction, and remain until all + * overlapping transactions complete. This even means that they + * must survive termination of the transaction's process. If a + * top level transaction is rolled back, however, it is immediately + * flagged so that it can be ignored, and its SIREAD locks can be + * released any time after that. + * + * (5) The only transactions which create SIREAD locks or check for + * conflicts with them are serializable transactions. + * + * (6) When a write lock for a top level transaction is found to cover + * an existing SIREAD lock for the same transaction, the SIREAD lock + * can be deleted. + * + * (7) A write from a serializable transaction must ensure that a xact + * record exists for the transaction, with the same lifespan (until + * all concurrent transaction complete or the transaction is rolled + * back) so that rw-dependencies to that transaction can be + * detected. + * + * We use an optimization for read-only transactions. Under certain + * circumstances, a read-only transaction's snapshot can be shown to + * never have conflicts with other transactions. This is referred to + * as a "safe" snapshot (and one known not to be is "unsafe"). + * However, it can't be determined whether a snapshot is safe until + * all concurrent read/write transactions complete. + * + * Once a read-only transaction is known to have a safe snapshot, it + * can release its predicate locks and exempt itself from further + * predicate lock tracking. READ ONLY DEFERRABLE transactions run only + * on safe snapshots, waiting as necessary for one to be available. + * + * + * Lightweight locks to manage access to the predicate locking shared + * memory objects must be taken in this order, and should be released in + * reverse order: + * + * SerializableFinishedListLock + * - Protects the list of transactions which have completed but which + * may yet matter because they overlap still-active transactions. + * + * SerializablePredicateLockListLock + * - Protects the linked list of locks held by a transaction. Note + * that the locks themselves are also covered by the partition + * locks of their respective lock targets; this lock only affects + * the linked list connecting the locks related to a transaction. + * - All transactions share this single lock (with no partitioning). + * - There is never a need for a process other than the one running + * an active transaction to walk the list of locks held by that + * transaction. + * - It is relatively infrequent that another process needs to + * modify the list for a transaction, but it does happen for such + * things as index page splits for pages with predicate locks and + * freeing of predicate locked pages by a vacuum process. When + * removing a lock in such cases, the lock itself contains the + * pointers needed to remove it from the list. When adding a + * lock in such cases, the lock can be added using the anchor in + * the transaction structure. Neither requires walking the list. + * - Cleaning up the list for a terminated transaction is sometimes + * not done on a retail basis, in which case no lock is required. + * - Due to the above, a process accessing its active transaction's + * list always uses a shared lock, regardless of whether it is + * walking or maintaining the list. This improves concurrency + * for the common access patterns. + * - A process which needs to alter the list of a transaction other + * than its own active transaction must acquire an exclusive + * lock. + * + * FirstPredicateLockMgrLock based partition locks + * - The same lock protects a target, all locks on that target, and + * the linked list of locks on the target.. + * - When more than one is needed, acquire in ascending order. + * + * SerializableXactHashLock + * - Protects both PredXact and SerializableXidHash. + * + * PredicateLockNextRowLinkLock + * - Protects the priorVersionOfRow and nextVersionOfRow fields of + * PREDICATELOCKTARGET when linkage is being created or destroyed. + * + * + * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/backend/storage/lmgr/predicate.c + * + *------------------------------------------------------------------------- + */ +/* + * INTERFACE ROUTINES + * + * housekeeping for setting up shared memory predicate lock structures + * InitPredicateLocks(void) + * PredicateLockShmemSize(void) + * + * predicate lock reporting + * GetPredicateLockStatusData(void) + * PageIsPredicateLocked(Relation relation, BlockNumber blkno) + * + * predicate lock maintenance + * RegisterSerializableTransaction(Snapshot snapshot) + * RegisterPredicateLockingXid(void) + * PredicateLockRelation(Relation relation) + * PredicateLockPage(Relation relation, BlockNumber blkno) + * PredicateLockTuple(Relation relation, HeapTuple tuple) + * PredicateLockPageSplit(Relation relation, BlockNumber oldblkno, + * BlockNumber newblkno); + * PredicateLockPageCombine(Relation relation, BlockNumber oldblkno, + * BlockNumber newblkno); + * PredicateLockTupleRowVersionLink(const Relation relation, + * const HeapTuple oldTuple, + * const HeapTuple newTuple) + * ReleasePredicateLocks(bool isCommit) + * + * conflict detection (may also trigger rollback) + * CheckForSerializableConflictOut(bool visible, Relation relation, + * HeapTupleData *tup, Buffer buffer) + * CheckForSerializableConflictIn(Relation relation, HeapTupleData *tup, + * Buffer buffer) + * + * final rollback checking + * PreCommit_CheckForSerializationFailure(void) + * + * two-phase commit support + * AtPrepare_PredicateLocks(void); + * PostPrepare_PredicateLocks(TransactionId xid); + * PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit); + * predicatelock_twophase_recover(TransactionId xid, uint16 info, + * void *recdata, uint32 len); + */ + +#include "postgres.h" + +#include "access/slru.h" +#include "access/subtrans.h" +#include "access/transam.h" +#include "access/twophase.h" +#include "access/twophase_rmgr.h" +#include "access/xact.h" +#include "miscadmin.h" +#include "storage/bufmgr.h" +#include "storage/predicate.h" +#include "storage/predicate_internals.h" +#include "storage/procarray.h" +#include "utils/rel.h" +#include "utils/snapmgr.h" +#include "utils/tqual.h" + +/* Uncomment the next line to test the graceful degradation code. */ +/* #define TEST_OLDSERXID */ + +/* + * Test the most selective fields first, for performance. + * + * a is covered by b if all of the following hold: + * 1) a.database = b.database + * 2) a.relation = b.relation + * 3) b.offset is invalid (b is page-granularity or higher) + * 4) either of the following: + * 4a) a.offset is valid (a is tuple-granularity) and a.page = b.page + * or 4b) a.offset is invalid and b.page is invalid (a is + * page-granularity and b is relation-granularity + */ +#define TargetTagIsCoveredBy(covered_target, covering_target) \ + ((GET_PREDICATELOCKTARGETTAG_RELATION(covered_target) == /* (2) */ \ + GET_PREDICATELOCKTARGETTAG_RELATION(covering_target)) \ + && (GET_PREDICATELOCKTARGETTAG_OFFSET(covering_target) == \ + InvalidOffsetNumber) /* (3) */ \ + && (((GET_PREDICATELOCKTARGETTAG_OFFSET(covered_target) != \ + InvalidOffsetNumber) /* (4a) */ \ + && (GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) == \ + GET_PREDICATELOCKTARGETTAG_PAGE(covered_target))) \ + || ((GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) == \ + InvalidBlockNumber) /* (4b) */ \ + && (GET_PREDICATELOCKTARGETTAG_PAGE(covered_target) \ + != InvalidBlockNumber))) \ + && (GET_PREDICATELOCKTARGETTAG_DB(covered_target) == /* (1) */ \ + GET_PREDICATELOCKTARGETTAG_DB(covering_target))) + +/* + * The predicate locking target and lock shared hash tables are partitioned to + * reduce contention. To determine which partition a given target belongs to, + * compute the tag's hash code with PredicateLockTargetTagHashCode(), then + * apply one of these macros. + * NB: NUM_PREDICATELOCK_PARTITIONS must be a power of 2! + */ +#define PredicateLockHashPartition(hashcode) \ + ((hashcode) % NUM_PREDICATELOCK_PARTITIONS) +#define PredicateLockHashPartitionLock(hashcode) \ + ((LWLockId) (FirstPredicateLockMgrLock + PredicateLockHashPartition(hashcode))) + +#define NPREDICATELOCKTARGETENTS() \ + mul_size(max_predicate_locks_per_xact, add_size(MaxBackends, max_prepared_xacts)) + +#define SxactIsOnFinishedList(sxact) (!SHMQueueIsDetached(&((sxact)->finishedLink))) + +#define SxactIsPrepared(sxact) (((sxact)->flags & SXACT_FLAG_PREPARED) != 0) +#define SxactIsCommitted(sxact) (((sxact)->flags & SXACT_FLAG_COMMITTED) != 0) +#define SxactIsRolledBack(sxact) (((sxact)->flags & SXACT_FLAG_ROLLED_BACK) != 0) +#define SxactIsReadOnly(sxact) (((sxact)->flags & SXACT_FLAG_READ_ONLY) != 0) +#define SxactHasSummaryConflictIn(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_IN) != 0) +#define SxactHasSummaryConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_OUT) != 0) +#define SxactHasConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_CONFLICT_OUT) != 0) +#define SxactIsDeferrableWaiting(sxact) (((sxact)->flags & SXACT_FLAG_DEFERRABLE_WAITING) != 0) +#define SxactIsROSafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_SAFE) != 0) +#define SxactIsROUnsafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_UNSAFE) != 0) +#define SxactIsMarkedForDeath(sxact) (((sxact)->flags & SXACT_FLAG_MARKED_FOR_DEATH) != 0) + +/* + * When a public interface method is called for a split on an index relation, + * this is the test to see if we should do a quick return. + */ +#define SkipSplitTracking(relation) \ + (((relation)->rd_id < FirstBootstrapObjectId) \ + || RelationUsesLocalBuffers(relation)) + +/* + * When a public interface method is called for serializing a relation within + * the current transaction, this is the test to see if we should do a quick + * return. + */ +#define SkipSerialization(relation) \ + ((!IsolationIsSerializable()) \ + || ((MySerializableXact == InvalidSerializableXact)) \ + || ReleasePredicateLocksIfROSafe() \ + || SkipSplitTracking(relation)) + + +/* + * Compute the hash code associated with a PREDICATELOCKTARGETTAG. + * + * To avoid unnecessary recomputations of the hash code, we try to do this + * just once per function, and then pass it around as needed. Aside from + * passing the hashcode to hash_search_with_hash_value(), we can extract + * the lock partition number from the hashcode. + */ +#define PredicateLockTargetTagHashCode(predicatelocktargettag) \ + (tag_hash((predicatelocktargettag), sizeof(PREDICATELOCKTARGETTAG))) + +/* + * Given a predicate lock tag, and the hash for its target, + * compute the lock hash. + * + * To make the hash code also depend on the transaction, we xor the sxid + * struct's address into the hash code, left-shifted so that the + * partition-number bits don't change. Since this is only a hash, we + * don't care if we lose high-order bits of the address; use an + * intermediate variable to suppress cast-pointer-to-int warnings. + */ +#define PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash) \ + ((targethash) ^ ((uint32) PointerGetDatum((predicatelocktag)->myXact)) \ + << LOG2_NUM_PREDICATELOCK_PARTITIONS) + + +/* + * The SLRU buffer area through which we access the old xids. + */ +static SlruCtlData OldSerXidSlruCtlData; + +#define OldSerXidSlruCtl (&OldSerXidSlruCtlData) + +#define OLDSERXID_PAGESIZE BLCKSZ +#define OLDSERXID_ENTRYSIZE sizeof(SerCommitSeqNo) +#define OLDSERXID_ENTRIESPERPAGE (OLDSERXID_PAGESIZE / OLDSERXID_ENTRYSIZE) +#define OLDSERXID_MAX_PAGE (SLRU_PAGES_PER_SEGMENT * 0x10000 - 1) + +#define OldSerXidNextPage(page) (((page) >= OLDSERXID_MAX_PAGE) ? 0 : (page) + 1) + +#define OldSerXidValue(slotno, xid) (*((SerCommitSeqNo *) \ + (OldSerXidSlruCtl->shared->page_buffer[slotno] + \ + ((((uint32) (xid)) % OLDSERXID_ENTRIESPERPAGE) * OLDSERXID_ENTRYSIZE)))) + +#define OldSerXidPage(xid) ((((uint32) (xid)) / OLDSERXID_ENTRIESPERPAGE) % (OLDSERXID_MAX_PAGE + 1)) +#define OldSerXidSegment(page) ((page) / SLRU_PAGES_PER_SEGMENT) + +typedef struct OldSerXidControlData +{ + int headPage; + int tailSegment; + TransactionId headXid; + TransactionId tailXid; + bool warningIssued; +} OldSerXidControlData; + +typedef struct OldSerXidControlData *OldSerXidControl; + +static OldSerXidControl oldSerXidControl; + +/* + * When the oldest committed transaction on the "finished" list is moved to + * SLRU, its predicate locks will be moved to this "dummy" transaction, + * collapsing duplicate targets. When a duplicate is found, the later + * commitSeqNo is used. + */ +static SERIALIZABLEXACT *OldCommittedSxact; + + +/* This configuration variable is used to set the predicate lock table size */ +int max_predicate_locks_per_xact; /* set by guc.c */ + +/* + * This provides a list of objects in order to track transactions + * participating in predicate locking. Entries in the list are fixed size, + * and reside in shared memory. The memory address of an entry must remain + * fixed during its lifetime. The list will be protected from concurrent + * update externally; no provision is made in this code to manage that. The + * number of entries in the list, and the size allowed for each entry is + * fixed upon creation. + */ +static PredXactList PredXact; + +/* + * This provides a pool of RWConflict data elements to use in conflict lists + * between transactions. + */ +static RWConflictPoolHeader RWConflictPool; + +/* + * The predicate locking hash tables are in shared memory. + * Each backend keeps pointers to them. + */ +static HTAB *SerializableXidHash; +static HTAB *PredicateLockTargetHash; +static HTAB *PredicateLockHash; +static SHM_QUEUE *FinishedSerializableTransactions; + +/* + * Tag for a reserved entry in PredicateLockTargetHash; used to ensure + * there's an element available for scratch space if we need it, + * e.g. in PredicateLockPageSplit. This is an otherwise-invalid tag. + */ +static const PREDICATELOCKTARGETTAG ReservedTargetTag = {0, 0, 0, 0, 0}; + +/* + * The local hash table used to determine when to combine multiple fine- + * grained locks into a single courser-grained lock. + */ +static HTAB *LocalPredicateLockHash = NULL; + +/* + * Keep a pointer to the currently-running serializable transaction (if any) + * for quick reference. + * TODO SSI: Remove volatile qualifier and the then-unnecessary casts? + */ +static volatile SERIALIZABLEXACT *MySerializableXact = InvalidSerializableXact; + +/* local functions */ + +static SERIALIZABLEXACT *CreatePredXact(void); +static void ReleasePredXact(SERIALIZABLEXACT *sxact); +static SERIALIZABLEXACT *FirstPredXact(void); +static SERIALIZABLEXACT *NextPredXact(SERIALIZABLEXACT *sxact); + +static bool RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer); +static void SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer); +static void SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact, SERIALIZABLEXACT *activeXact); +static void ReleaseRWConflict(RWConflict conflict); +static void FlagSxactUnsafe(SERIALIZABLEXACT *sxact); + +static bool OldSerXidPagePrecedesLogically(int p, int q); +static void OldSerXidInit(void); +static void OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo); +static SerCommitSeqNo OldSerXidGetMinConflictCommitSeqNo(TransactionId xid); +static void OldSerXidSetActiveSerXmin(TransactionId xid); + +static uint32 predicatelock_hash(const void *key, Size keysize); +static void SummarizeOldestCommittedSxact(void); +static Snapshot GetSafeSnapshot(Snapshot snapshot); +static Snapshot RegisterSerializableTransactionInt(Snapshot snapshot); +static bool PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag); +static bool GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag, + PREDICATELOCKTARGETTAG *parent); +static bool CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag); +static void RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target, + uint32 targettaghash); +static void DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag); +static int PredicateLockPromotionThreshold(const PREDICATELOCKTARGETTAG *tag); +static bool CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag); +static void DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag); +static void CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag, + uint32 targettaghash, + SERIALIZABLEXACT *sxact); +static void DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash); +static bool TransferPredicateLocksToNewTarget(const PREDICATELOCKTARGETTAG oldtargettag, + const PREDICATELOCKTARGETTAG newtargettag, + bool removeOld); +static void PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag); +static void SetNewSxactGlobalXmin(void); +static bool ReleasePredicateLocksIfROSafe(void); +static void ClearOldPredicateLocks(void); +static void ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial, + bool summarize); +static bool XidIsConcurrent(TransactionId xid); +static void CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag); +static bool CheckSingleTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag, + PREDICATELOCKTARGETTAG *nexttargettag); +static void FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer); +static void OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader, + SERIALIZABLEXACT *writer); + +/*------------------------------------------------------------------------*/ + +/* + * These functions are a simple implementation of a list for this specific + * type of struct. If there is ever a generalized shared memory list, we + * should probably switch to that. + */ +static SERIALIZABLEXACT * +CreatePredXact(void) +{ + PredXactListElement ptle; + + ptle = (PredXactListElement) + SHMQueueNext(&PredXact->availableList, + &PredXact->availableList, + offsetof(PredXactListElementData, link)); + if (!ptle) + return NULL; + + SHMQueueDelete(&ptle->link); + SHMQueueInsertBefore(&PredXact->activeList, &ptle->link); + return &ptle->sxact; +} + +static void +ReleasePredXact(SERIALIZABLEXACT *sxact) +{ + PredXactListElement ptle; + + Assert(ShmemAddrIsValid(sxact)); + + ptle = (PredXactListElement) + (((char *) sxact) + - offsetof(PredXactListElementData, sxact) + +offsetof(PredXactListElementData, link)); + SHMQueueDelete(&ptle->link); + SHMQueueInsertBefore(&PredXact->availableList, &ptle->link); +} + +static SERIALIZABLEXACT * +FirstPredXact(void) +{ + PredXactListElement ptle; + + ptle = (PredXactListElement) + SHMQueueNext(&PredXact->activeList, + &PredXact->activeList, + offsetof(PredXactListElementData, link)); + if (!ptle) + return NULL; + + return &ptle->sxact; +} + +static SERIALIZABLEXACT * +NextPredXact(SERIALIZABLEXACT *sxact) +{ + PredXactListElement ptle; + + Assert(ShmemAddrIsValid(sxact)); + + ptle = (PredXactListElement) + (((char *) sxact) + - offsetof(PredXactListElementData, sxact) + +offsetof(PredXactListElementData, link)); + ptle = (PredXactListElement) + SHMQueueNext(&PredXact->activeList, + &ptle->link, + offsetof(PredXactListElementData, link)); + if (!ptle) + return NULL; + + return &ptle->sxact; +} + +/*------------------------------------------------------------------------*/ + +/* + * These functions manage primitive access to the RWConflict pool and lists. + */ +static bool +RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer) +{ + RWConflict conflict; + + Assert(reader != writer); + + /* Check the ends of the purported conflict first. */ + if (SxactIsRolledBack(reader) + || SxactIsRolledBack(writer) + || SHMQueueEmpty(&reader->outConflicts) + || SHMQueueEmpty(&writer->inConflicts)) + return false; + + /* A conflict is possible; walk the list to find out. */ + conflict = (RWConflict) + SHMQueueNext(&reader->outConflicts, + &reader->outConflicts, + offsetof(RWConflictData, outLink)); + while (conflict) + { + if (conflict->sxactIn == writer) + return true; + conflict = (RWConflict) + SHMQueueNext(&reader->outConflicts, + &conflict->outLink, + offsetof(RWConflictData, outLink)); + } + + /* No conflict found. */ + return false; +} + +static void +SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer) +{ + RWConflict conflict; + + Assert(reader != writer); + Assert(!RWConflictExists(reader, writer)); + + conflict = (RWConflict) + SHMQueueNext(&RWConflictPool->availableList, + &RWConflictPool->availableList, + offsetof(RWConflictData, outLink)); + if (!conflict) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("not enough elements in RWConflictPool to record a rw-conflict"), + errhint("You might need to run fewer transactions at a time or increase max_connections."))); + + SHMQueueDelete(&conflict->outLink); + + conflict->sxactOut = reader; + conflict->sxactIn = writer; + SHMQueueInsertBefore(&reader->outConflicts, &conflict->outLink); + SHMQueueInsertBefore(&writer->inConflicts, &conflict->inLink); +} + +static void +SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact, + SERIALIZABLEXACT *activeXact) +{ + RWConflict conflict; + + Assert(roXact != activeXact); + Assert(SxactIsReadOnly(roXact)); + Assert(!SxactIsReadOnly(activeXact)); + + conflict = (RWConflict) + SHMQueueNext(&RWConflictPool->availableList, + &RWConflictPool->availableList, + offsetof(RWConflictData, outLink)); + if (!conflict) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("not enough elements in RWConflictPool to record a potential rw-conflict"), + errhint("You might need to run fewer transactions at a time or increase max_connections."))); + + SHMQueueDelete(&conflict->outLink); + + conflict->sxactOut = activeXact; + conflict->sxactIn = roXact; + SHMQueueInsertBefore(&activeXact->possibleUnsafeConflicts, + &conflict->outLink); + SHMQueueInsertBefore(&roXact->possibleUnsafeConflicts, + &conflict->inLink); +} + +static void +ReleaseRWConflict(RWConflict conflict) +{ + SHMQueueDelete(&conflict->inLink); + SHMQueueDelete(&conflict->outLink); + SHMQueueInsertBefore(&RWConflictPool->availableList, &conflict->outLink); +} + +static void +FlagSxactUnsafe(SERIALIZABLEXACT *sxact) +{ + RWConflict conflict, + nextConflict; + + Assert(SxactIsReadOnly(sxact)); + Assert(!SxactIsROSafe(sxact)); + + sxact->flags |= SXACT_FLAG_RO_UNSAFE; + + /* + * We know this isn't a safe snapshot, so we can stop looking for other + * potential conflicts. + */ + conflict = (RWConflict) + SHMQueueNext(&sxact->possibleUnsafeConflicts, + &sxact->possibleUnsafeConflicts, + offsetof(RWConflictData, inLink)); + while (conflict) + { + nextConflict = (RWConflict) + SHMQueueNext(&sxact->possibleUnsafeConflicts, + &conflict->inLink, + offsetof(RWConflictData, inLink)); + + Assert(!SxactIsReadOnly(conflict->sxactOut)); + Assert(sxact == conflict->sxactIn); + + ReleaseRWConflict(conflict); + + conflict = nextConflict; + } +} + +/*------------------------------------------------------------------------*/ + +/* + * We will work on the page range of 0..OLDSERXID_MAX_PAGE. + * Compares using wraparound logic, as is required by slru.c. + */ +static bool +OldSerXidPagePrecedesLogically(int p, int q) +{ + int diff; + + /* + * We have to compare modulo (OLDSERXID_MAX_PAGE+1)/2. Both inputs should + * be in the range 0..OLDSERXID_MAX_PAGE. + */ + Assert(p >= 0 && p <= OLDSERXID_MAX_PAGE); + Assert(q >= 0 && q <= OLDSERXID_MAX_PAGE); + + diff = p - q; + if (diff >= ((OLDSERXID_MAX_PAGE + 1) / 2)) + diff -= OLDSERXID_MAX_PAGE + 1; + else if (diff < -((OLDSERXID_MAX_PAGE + 1) / 2)) + diff += OLDSERXID_MAX_PAGE + 1; + return diff < 0; +} + +/* + * Initialize for the tracking of old serializable committed xids. + */ +static void +OldSerXidInit(void) +{ + bool found; + + /* + * Set up SLRU management of the pg_serial data. + */ + OldSerXidSlruCtl->PagePrecedes = OldSerXidPagePrecedesLogically; + SimpleLruInit(OldSerXidSlruCtl, "OldSerXid SLRU Ctl", NUM_OLDSERXID_BUFFERS, 0, + OldSerXidLock, "pg_serial"); + /* Override default assumption that writes should be fsync'd */ + OldSerXidSlruCtl->do_fsync = false; + + /* + * Create or attach to the OldSerXidControl structure. + */ + oldSerXidControl = (OldSerXidControl) + ShmemInitStruct("OldSerXidControlData", sizeof(OldSerXidControlData), &found); + + if (!found) + { + /* + * Set control information to reflect empty SLRU. + */ + oldSerXidControl->headPage = -1; + oldSerXidControl->tailSegment = -1; + oldSerXidControl->headXid = InvalidTransactionId; + oldSerXidControl->tailXid = InvalidTransactionId; + oldSerXidControl->warningIssued = false; + } +} + +/* + * Record a committed read write serializable xid and the minimum + * commitSeqNo of any transactions to which this xid had a rw-conflict out. + * A zero seqNo means that there were no conflicts out from xid. + * + * The return value is normally false -- true means that we're about to + * wrap around our space for tracking these xids, so the caller might want + * to take action to prevent that. + */ +static void +OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo) +{ + TransactionId tailXid; + int targetPage; + int slotno; + int page; + int xidSpread; + bool isNewPage; + + Assert(TransactionIdIsValid(xid)); + + targetPage = OldSerXidPage(xid); + + LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE); + + /* + * If no serializable transactions are active, there shouldn't be anything + * to push out to this SLRU. Hitting this assert would mean there's + * something wrong with the earlier cleanup logic. + */ + tailXid = oldSerXidControl->tailXid; + Assert(TransactionIdIsValid(tailXid)); + + if (oldSerXidControl->headPage < 0) + { + page = OldSerXidPage(tailXid); + oldSerXidControl->tailSegment = OldSerXidSegment(page); + page = oldSerXidControl->tailSegment * OLDSERXID_ENTRIESPERPAGE; + isNewPage = true; + } + else + { + page = OldSerXidNextPage(oldSerXidControl->headPage); + isNewPage = OldSerXidPagePrecedesLogically(oldSerXidControl->headPage, targetPage); + } + + if (!TransactionIdIsValid(oldSerXidControl->headXid) + || TransactionIdFollows(xid, oldSerXidControl->headXid)) + oldSerXidControl->headXid = xid; + if (oldSerXidControl->headPage < 0 + || OldSerXidPagePrecedesLogically(oldSerXidControl->headPage, targetPage)) + oldSerXidControl->headPage = targetPage; + + xidSpread = (((uint32) xid) - ((uint32) tailXid)); + if (oldSerXidControl->warningIssued) + { + if (xidSpread < 800000000) + oldSerXidControl->warningIssued = false; + } + else if (xidSpread >= 1000000000) + { + oldSerXidControl->warningIssued = true; + ereport(WARNING, + (errmsg("memory for serializable conflict tracking is nearly exhausted"), + errhint("There may be an idle transaction or a forgotten prepared transaction causing this."))); + } + + if (isNewPage) + { + /* Initialize intervening pages. */ + while (page != targetPage) + { + (void) SimpleLruZeroPage(OldSerXidSlruCtl, page); + page = OldSerXidNextPage(page); + } + slotno = SimpleLruZeroPage(OldSerXidSlruCtl, targetPage); + } + else + slotno = SimpleLruReadPage(OldSerXidSlruCtl, targetPage, true, xid); + + OldSerXidValue(slotno, xid) = minConflictCommitSeqNo; + + LWLockRelease(OldSerXidLock); +} + +/* + * Get the minimum commitSeqNo for any conflict out for the given xid. For + * a transaction which exists but has no conflict out, InvalidSerCommitSeqNo + * will be returned. + */ +static SerCommitSeqNo +OldSerXidGetMinConflictCommitSeqNo(TransactionId xid) +{ + TransactionId headXid; + TransactionId tailXid; + SerCommitSeqNo val; + int slotno; + + Assert(TransactionIdIsValid(xid)); + + LWLockAcquire(OldSerXidLock, LW_SHARED); + headXid = oldSerXidControl->headXid; + tailXid = oldSerXidControl->tailXid; + LWLockRelease(OldSerXidLock); + + if (!TransactionIdIsValid(headXid)) + return 0; + + Assert(TransactionIdIsValid(tailXid)); + + if (TransactionIdPrecedes(xid, tailXid) + || TransactionIdFollows(xid, headXid)) + return 0; + + /* + * The following function must be called without holding OldSerXidLock, + * but will return with that lock held, which must then be released. + */ + slotno = SimpleLruReadPage_ReadOnly(OldSerXidSlruCtl, + OldSerXidPage(xid), xid); + val = OldSerXidValue(slotno, xid); + LWLockRelease(OldSerXidLock); + return val; +} + +/* + * Call this whenever there is a new xmin for active serializable + * transactions. We don't need to keep information on transactions which + * preceed that. InvalidTransactionId means none active, so everything in + * the SLRU should be discarded. + */ +static void +OldSerXidSetActiveSerXmin(TransactionId xid) +{ + int newTailPage; + int newTailSegment; + + LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE); + + /* + * When no sxacts are active, nothing overlaps, set the xid values to + * invalid to show that there are no valid entries. Don't clear the + * segment/page information, though. A new xmin might still land in an + * existing segment, and we don't want to repeatedly delete and re-create + * the same segment file. + */ + if (!TransactionIdIsValid(xid)) + { + if (TransactionIdIsValid(oldSerXidControl->tailXid)) + { + oldSerXidControl->headXid = InvalidTransactionId; + oldSerXidControl->tailXid = InvalidTransactionId; + } + LWLockRelease(OldSerXidLock); + return; + } + + /* + * When we're recovering prepared transactions, the global xmin might move + * backwards depending on the order they're recovered. Normally that's not + * OK, but during recovery no serializable transactions will commit, so + * the SLRU is empty and we can get away with it. + */ + if (RecoveryInProgress()) + { + Assert(oldSerXidControl->headPage < 0); + if (!TransactionIdIsValid(oldSerXidControl->tailXid) + || TransactionIdPrecedes(xid, oldSerXidControl->tailXid)) + oldSerXidControl->tailXid = xid; + LWLockRelease(OldSerXidLock); + return; + } + + Assert(!TransactionIdIsValid(oldSerXidControl->tailXid) + || TransactionIdFollows(xid, oldSerXidControl->tailXid)); + + oldSerXidControl->tailXid = xid; + + /* Exit quickly if there are no segments active. */ + if (oldSerXidControl->headPage < 0) + { + LWLockRelease(OldSerXidLock); + return; + } + + newTailPage = OldSerXidPage(xid); + newTailSegment = OldSerXidSegment(newTailPage); + + /* Exit quickly if we're still on the same segment. */ + if (newTailSegment == oldSerXidControl->tailSegment) + { + LWLockRelease(OldSerXidLock); + return; + } + + oldSerXidControl->tailSegment = newTailSegment; + + /* See if that has cleared the last segment. */ + if (OldSerXidPagePrecedesLogically(oldSerXidControl->headPage, + newTailSegment * SLRU_PAGES_PER_SEGMENT)) + { + oldSerXidControl->headXid = InvalidTransactionId; + oldSerXidControl->headPage = -1; + oldSerXidControl->tailSegment = -1; + } + + LWLockRelease(OldSerXidLock); + + SimpleLruTruncate(OldSerXidSlruCtl, newTailPage); +} + +/*------------------------------------------------------------------------*/ + +/* + * InitPredicateLocks -- Initialize the predicate locking data structures. + * + * This is called from CreateSharedMemoryAndSemaphores(), which see for + * more comments. In the normal postmaster case, the shared hash tables + * are created here. Backends inherit the pointers + * to the shared tables via fork(). In the EXEC_BACKEND case, each + * backend re-executes this code to obtain pointers to the already existing + * shared hash tables. + */ +void +InitPredicateLocks(void) +{ + HASHCTL info; + int hash_flags; + long init_table_size, + max_table_size; + Size requestSize; + bool found; + + /* + * Compute init/max size to request for predicate lock target hashtable. + * Note these calculations must agree with PredicateLockShmemSize! + */ + max_table_size = NPREDICATELOCKTARGETENTS(); + init_table_size = max_table_size / 2; + + /* + * Allocate hash table for PREDICATELOCKTARGET structs. This stores + * per-predicate-lock-target information. + */ + MemSet(&info, 0, sizeof(info)); + info.keysize = sizeof(PREDICATELOCKTARGETTAG); + info.entrysize = sizeof(PREDICATELOCKTARGET); + info.hash = tag_hash; + info.num_partitions = NUM_PREDICATELOCK_PARTITIONS; + hash_flags = (HASH_ELEM | HASH_FUNCTION | HASH_PARTITION); + + PredicateLockTargetHash = ShmemInitHash("PREDICATELOCKTARGET hash", + init_table_size, + max_table_size, + &info, + hash_flags); + + /* Assume an average of 2 xacts per target */ + max_table_size *= 2; + init_table_size *= 2; + + /* + * Reserve an entry in the hash table; we use it to make sure there's + * always one entry available when we need to split or combine a page, + * because running out of space there could mean aborting a + * non-serializable transaction. + */ + hash_search(PredicateLockTargetHash, &ReservedTargetTag, + HASH_ENTER, NULL); + + + /* + * Allocate hash table for PREDICATELOCK structs. This stores per + * xact-lock-of-a-target information. + */ + MemSet(&info, 0, sizeof(info)); + info.keysize = sizeof(PREDICATELOCKTAG); + info.entrysize = sizeof(PREDICATELOCK); + info.hash = predicatelock_hash; + info.num_partitions = NUM_PREDICATELOCK_PARTITIONS; + hash_flags = (HASH_ELEM | HASH_FUNCTION | HASH_PARTITION); + + PredicateLockHash = ShmemInitHash("PREDICATELOCK hash", + init_table_size, + max_table_size, + &info, + hash_flags); + + /* + * Compute init/max size to request for serializable transaction + * hashtable. Note these calculations must agree with + * PredicateLockShmemSize! + */ + max_table_size = (MaxBackends + max_prepared_xacts); + init_table_size = max_table_size / 2; + + /* + * Allocate a list to hold information on transactions participating in + * predicate locking. + * + * Assume an average of 10 predicate locking transactions per backend. + * This allows aggressive cleanup while detail is present before data must + * be summarized for storage in SLRU and the "dummy" transaction. + */ + max_table_size *= 10; + init_table_size *= 10; + + PredXact = ShmemInitStruct("PredXactList", + PredXactListDataSize, + &found); + if (!found) + { + int i; + + SHMQueueInit(&PredXact->availableList); + SHMQueueInit(&PredXact->activeList); + PredXact->SxactGlobalXmin = InvalidTransactionId; + PredXact->SxactGlobalXminCount = 0; + PredXact->WritableSxactCount = 0; + PredXact->LastSxactCommitSeqNo = FirstNormalSerCommitSeqNo - 1; + PredXact->CanPartialClearThrough = 0; + PredXact->HavePartialClearedThrough = 0; + PredXact->NeedTargetLinkCleanup = false; + requestSize = mul_size((Size) max_table_size, + PredXactListElementDataSize); + PredXact->element = ShmemAlloc(requestSize); + if (PredXact->element == NULL) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("not enough shared memory for elements of data structure" + " \"%s\" (%lu bytes requested)", + "PredXactList", (unsigned long) requestSize))); + /* Add all elements to available list, clean. */ + memset(PredXact->element, 0, requestSize); + for (i = 0; i < max_table_size; i++) + { + SHMQueueInsertBefore(&(PredXact->availableList), + &(PredXact->element[i].link)); + } + PredXact->OldCommittedSxact = CreatePredXact(); + SetInvalidVirtualTransactionId(PredXact->OldCommittedSxact->vxid); + PredXact->OldCommittedSxact->commitSeqNo = 0; + PredXact->OldCommittedSxact->SeqNo.lastCommitBeforeSnapshot = 0; + SHMQueueInit(&PredXact->OldCommittedSxact->outConflicts); + SHMQueueInit(&PredXact->OldCommittedSxact->inConflicts); + SHMQueueInit(&PredXact->OldCommittedSxact->predicateLocks); + SHMQueueInit(&PredXact->OldCommittedSxact->finishedLink); + SHMQueueInit(&PredXact->OldCommittedSxact->possibleUnsafeConflicts); + PredXact->OldCommittedSxact->topXid = InvalidTransactionId; + PredXact->OldCommittedSxact->finishedBefore = InvalidTransactionId; + PredXact->OldCommittedSxact->xmin = InvalidTransactionId; + PredXact->OldCommittedSxact->flags = SXACT_FLAG_COMMITTED; + PredXact->OldCommittedSxact->pid = 0; + } + /* This never changes, so let's keep a local copy. */ + OldCommittedSxact = PredXact->OldCommittedSxact; + + /* + * Allocate hash table for SERIALIZABLEXID structs. This stores per-xid + * information for serializable transactions which have accessed data. + */ + MemSet(&info, 0, sizeof(info)); + info.keysize = sizeof(SERIALIZABLEXIDTAG); + info.entrysize = sizeof(SERIALIZABLEXID); + info.hash = tag_hash; + hash_flags = (HASH_ELEM | HASH_FUNCTION); + + SerializableXidHash = ShmemInitHash("SERIALIZABLEXID hash", + init_table_size, + max_table_size, + &info, + hash_flags); + + /* + * Allocate space for tracking rw-conflicts in lists attached to the + * transactions. + * + * Assume an average of 5 conflicts per transaction. Calculations suggest + * that this will prevent resource exhaustion in even the most pessimal + * loads up to max_connections = 200 with all 200 connections pounding the + * database with serializable transactions. Beyond that, there may be + * occassional transactions canceled when trying to flag conflicts. That's + * probably OK. + */ + max_table_size *= 5; + + RWConflictPool = ShmemInitStruct("RWConflictPool", + RWConflictPoolHeaderDataSize, + &found); + if (!found) + { + int i; + + SHMQueueInit(&RWConflictPool->availableList); + requestSize = mul_size((Size) max_table_size, + PredXactListElementDataSize); + RWConflictPool->element = ShmemAlloc(requestSize); + if (RWConflictPool->element == NULL) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("not enough shared memory for elements of data structure" + " \"%s\" (%lu bytes requested)", + "RWConflictPool", (unsigned long) requestSize))); + /* Add all elements to available list, clean. */ + memset(RWConflictPool->element, 0, requestSize); + for (i = 0; i < max_table_size; i++) + { + SHMQueueInsertBefore(&(RWConflictPool->availableList), + &(RWConflictPool->element[i].outLink)); + } + } + + /* + * Create or attach to the header for the list of finished serializable + * transactions. + */ + FinishedSerializableTransactions = (SHM_QUEUE *) + ShmemInitStruct("FinishedSerializableTransactions", + sizeof(SHM_QUEUE), + &found); + if (!found) + SHMQueueInit(FinishedSerializableTransactions); + + /* + * Initialize the SLRU storage for old committed serializable + * transactions. + */ + OldSerXidInit(); +} + +/* + * Estimate shared-memory space used for predicate lock table + */ +Size +PredicateLockShmemSize(void) +{ + Size size = 0; + long max_table_size; + + /* predicate lock target hash table */ + max_table_size = NPREDICATELOCKTARGETENTS(); + size = add_size(size, hash_estimate_size(max_table_size, + sizeof(PREDICATELOCKTARGET))); + + /* predicate lock hash table */ + max_table_size *= 2; + size = add_size(size, hash_estimate_size(max_table_size, + sizeof(PREDICATELOCK))); + + /* + * Since NPREDICATELOCKTARGETENTS is only an estimate, add 10% safety + * margin. + */ + size = add_size(size, size / 10); + + /* transaction list */ + max_table_size = MaxBackends + max_prepared_xacts; + max_table_size *= 10; + size = add_size(size, PredXactListDataSize); + size = add_size(size, mul_size((Size) max_table_size, + PredXactListElementDataSize)); + + /* transaction xid table */ + size = add_size(size, hash_estimate_size(max_table_size, + sizeof(SERIALIZABLEXID))); + + /* Head for list of finished serializable transactions. */ + size = add_size(size, sizeof(SHM_QUEUE)); + + /* Shared memory structures for SLRU tracking of old committed xids. */ + size = add_size(size, sizeof(OldSerXidControl)); + size = add_size(size, SimpleLruShmemSize(NUM_OLDSERXID_BUFFERS, 0)); + + return size; +} + + +/* + * Compute the hash code associated with a PREDICATELOCKTAG. + * + * Because we want to use just one set of partition locks for both the + * PREDICATELOCKTARGET and PREDICATELOCK hash tables, we have to make sure + * that PREDICATELOCKs fall into the same partition number as their + * associated PREDICATELOCKTARGETs. dynahash.c expects the partition number + * to be the low-order bits of the hash code, and therefore a + * PREDICATELOCKTAG's hash code must have the same low-order bits as the + * associated PREDICATELOCKTARGETTAG's hash code. We achieve this with this + * specialized hash function. + */ +static uint32 +predicatelock_hash(const void *key, Size keysize) +{ + const PREDICATELOCKTAG *predicatelocktag = (const PREDICATELOCKTAG *) key; + uint32 targethash; + + Assert(keysize == sizeof(PREDICATELOCKTAG)); + + /* Look into the associated target object, and compute its hash code */ + targethash = PredicateLockTargetTagHashCode(&predicatelocktag->myTarget->tag); + + return PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash); +} + + +/* + * GetPredicateLockStatusData + * Return a table containing the internal state of the predicate + * lock manager for use in pg_lock_status. + * + * Like GetLockStatusData, this function tries to hold the partition LWLocks + * for as short a time as possible by returning two arrays that simply + * contain the PREDICATELOCKTARGETTAG and SERIALIZABLEXACT for each lock + * table entry. Multiple copies of the same PREDICATELOCKTARGETTAG and + * SERIALIZABLEXACT will likely appear. + */ +PredicateLockData * +GetPredicateLockStatusData(void) +{ + PredicateLockData *data; + int i; + int els, + el; + HASH_SEQ_STATUS seqstat; + PREDICATELOCK *predlock; + + data = (PredicateLockData *) palloc(sizeof(PredicateLockData)); + + /* + * To ensure consistency, take simultaneous locks on all partition locks + * in ascending order, then SerializableXactHashLock. + */ + for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++) + LWLockAcquire(FirstPredicateLockMgrLock + i, LW_SHARED); + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + + /* Get number of locks and allocate appropriately-sized arrays. */ + els = hash_get_num_entries(PredicateLockHash); + data->nelements = els; + data->locktags = (PREDICATELOCKTARGETTAG *) + palloc(sizeof(PREDICATELOCKTARGETTAG) * els); + data->xacts = (SERIALIZABLEXACT *) + palloc(sizeof(SERIALIZABLEXACT) * els); + + + /* Scan through PredicateLockHash and copy contents */ + hash_seq_init(&seqstat, PredicateLockHash); + + el = 0; + + while ((predlock = (PREDICATELOCK *) hash_seq_search(&seqstat))) + { + data->locktags[el] = predlock->tag.myTarget->tag; + data->xacts[el] = *predlock->tag.myXact; + el++; + } + + Assert(el == els); + + /* Release locks in reverse order */ + LWLockRelease(SerializableXactHashLock); + for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--) + LWLockRelease(FirstPredicateLockMgrLock + i); + + return data; +} + +/* + * Free up shared memory structures by pushing the oldest sxact (the one at + * the front of the SummarizeOldestCommittedSxact queue) into summary form. + * Each call will free exactly one SERIALIZABLEXACT structure and may also + * free one or more of these structures: SERIALIZABLEXID, PREDICATELOCK, + * PREDICATELOCKTARGET, RWConflictData. + */ +static void +SummarizeOldestCommittedSxact(void) +{ + SERIALIZABLEXACT *sxact; + + LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); + +#ifdef TEST_OLDSERXID + if (SHMQueueEmpty(FinishedSerializableTransactions)) + { + LWLockRelease(SerializableFinishedListLock); + return; + } +#else + Assert(!SHMQueueEmpty(FinishedSerializableTransactions)); +#endif + + /* + * Grab the first sxact off the finished list -- this will be the earliest + * commit. Remove it from the list. + */ + sxact = (SERIALIZABLEXACT *) + SHMQueueNext(FinishedSerializableTransactions, + FinishedSerializableTransactions, + offsetof(SERIALIZABLEXACT, finishedLink)); + SHMQueueDelete(&(sxact->finishedLink)); + + /* Add to SLRU summary information. */ + if (TransactionIdIsValid(sxact->topXid) && !SxactIsReadOnly(sxact)) + OldSerXidAdd(sxact->topXid, SxactHasConflictOut(sxact) + ? sxact->SeqNo.earliestOutConflictCommit : InvalidSerCommitSeqNo); + + /* Summarize and release the detail. */ + ReleaseOneSerializableXact(sxact, false, true); + + LWLockRelease(SerializableFinishedListLock); +} + +/* + * GetSafeSnapshot + * Obtain and register a snapshot for a READ ONLY DEFERRABLE + * transaction. Ensures that the snapshot is "safe", i.e. a + * read-only transaction running on it can execute serializably + * without further checks. This requires waiting for concurrent + * transactions to complete, and retrying with a new snapshot if + * one of them could possibly create a conflict. + */ +static Snapshot +GetSafeSnapshot(Snapshot origSnapshot) +{ + Snapshot snapshot; + + Assert(XactReadOnly && XactDeferrable); + + while (true) + { + /* + * RegisterSerializableTransactionInt is going to call + * GetSnapshotData, so we need to provide it the static snapshot our + * caller passed to us. It returns a copy of that snapshot and + * registers it on TopTransactionResourceOwner. + */ + snapshot = RegisterSerializableTransactionInt(origSnapshot); + + if (MySerializableXact == InvalidSerializableXact) + return snapshot; /* no concurrent r/w xacts; it's safe */ + + MySerializableXact->flags |= SXACT_FLAG_DEFERRABLE_WAITING; + + /* + * Wait for concurrent transactions to finish. Stop early if one of + * them marked us as conflicted. + */ + while (!(SHMQueueEmpty((SHM_QUEUE *) + &MySerializableXact->possibleUnsafeConflicts) || + SxactIsROUnsafe(MySerializableXact))) + ProcWaitForSignal(); + + MySerializableXact->flags &= ~SXACT_FLAG_DEFERRABLE_WAITING; + if (!SxactIsROUnsafe(MySerializableXact)) + break; /* success */ + + /* else, need to retry... */ + ereport(DEBUG2, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("deferrable snapshot was unsafe; trying a new one"))); + ReleasePredicateLocks(false); + UnregisterSnapshotFromOwner(snapshot, + TopTransactionResourceOwner); + } + + /* + * Now we have a safe snapshot, so we don't need to do any further checks. + */ + Assert(SxactIsROSafe(MySerializableXact)); + ReleasePredicateLocks(false); + + return snapshot; +} + +/* + * Acquire and register a snapshot which can be used for this transaction.. + * Make sure we have a SERIALIZABLEXACT reference in MySerializableXact. + * It should be current for this process and be contained in PredXact. + */ +Snapshot +RegisterSerializableTransaction(Snapshot snapshot) +{ + Assert(IsolationIsSerializable()); + + /* + * A special optimization is available for SERIALIZABLE READ ONLY + * DEFERRABLE transactions -- we can wait for a suitable snapshot and + * thereby avoid all SSI overhead once it's running.. + */ + if (XactReadOnly && XactDeferrable) + return GetSafeSnapshot(snapshot); + + return RegisterSerializableTransactionInt(snapshot); +} + +static Snapshot +RegisterSerializableTransactionInt(Snapshot snapshot) +{ + PGPROC *proc; + VirtualTransactionId vxid; + SERIALIZABLEXACT *sxact, + *othersxact; + HASHCTL hash_ctl; + + /* We only do this for serializable transactions. Once. */ + Assert(MySerializableXact == InvalidSerializableXact); + + Assert(!RecoveryInProgress()); + + proc = MyProc; + Assert(proc != NULL); + GET_VXID_FROM_PGPROC(vxid, *proc); + + /* + * First we get the sxact structure, which may involve looping and access + * to the "finished" list to free a structure for use. + */ +#ifdef TEST_OLDSERXID + SummarizeOldestCommittedSxact(); +#endif + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + do + { + sxact = CreatePredXact(); + /* If null, push out committed sxact to SLRU summary & retry. */ + if (!sxact) + { + LWLockRelease(SerializableXactHashLock); + SummarizeOldestCommittedSxact(); + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + } + } while (!sxact); + + /* Get and register a snapshot */ + snapshot = GetSnapshotData(snapshot); + snapshot = RegisterSnapshotOnOwner(snapshot, TopTransactionResourceOwner); + + /* + * If there are no serializable transactions which are not read-only, we + * can "opt out" of predicate locking and conflict checking for a + * read-only transaction. + * + * The reason this is safe is that a read-only transaction can only become + * part of a dangerous structure if it overlaps a writable transaction + * which in turn overlaps a writable transaction which committed before + * the read-only transaction started. A new writable transaction can + * overlap this one, but it can't meet the other condition of overlapping + * a transaction which committed before this one started. + */ + if (XactReadOnly && PredXact->WritableSxactCount == 0) + { + ReleasePredXact(sxact); + LWLockRelease(SerializableXactHashLock); + return snapshot; + } + + /* Maintain serializable global xmin info. */ + if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)) + { + Assert(PredXact->SxactGlobalXminCount == 0); + PredXact->SxactGlobalXmin = snapshot->xmin; + PredXact->SxactGlobalXminCount = 1; + OldSerXidSetActiveSerXmin(snapshot->xmin); + } + else if (TransactionIdEquals(snapshot->xmin, PredXact->SxactGlobalXmin)) + { + Assert(PredXact->SxactGlobalXminCount > 0); + PredXact->SxactGlobalXminCount++; + } + else + { + Assert(TransactionIdFollows(snapshot->xmin, PredXact->SxactGlobalXmin)); + } + + /* Initialize the structure. */ + sxact->vxid = vxid; + sxact->SeqNo.lastCommitBeforeSnapshot = PredXact->LastSxactCommitSeqNo; + sxact->commitSeqNo = InvalidSerCommitSeqNo; + SHMQueueInit(&(sxact->outConflicts)); + SHMQueueInit(&(sxact->inConflicts)); + SHMQueueInit(&(sxact->possibleUnsafeConflicts)); + sxact->topXid = GetTopTransactionIdIfAny(); + sxact->finishedBefore = InvalidTransactionId; + sxact->xmin = snapshot->xmin; + sxact->pid = MyProcPid; + SHMQueueInit(&(sxact->predicateLocks)); + SHMQueueElemInit(&(sxact->finishedLink)); + sxact->flags = 0; + if (XactReadOnly) + { + sxact->flags |= SXACT_FLAG_READ_ONLY; + + /* + * Register all concurrent r/w transactions as possible conflicts; if + * all of them commit without any outgoing conflicts to earlier + * transactions then this snapshot can be deemed safe (and we can run + * without tracking predicate locks). + */ + for (othersxact = FirstPredXact(); + othersxact != NULL; + othersxact = NextPredXact(othersxact)) + { + if (!SxactIsOnFinishedList(othersxact) && + !SxactIsReadOnly(othersxact)) + { + SetPossibleUnsafeConflict(sxact, othersxact); + } + } + } + else + { + ++(PredXact->WritableSxactCount); + Assert(PredXact->WritableSxactCount <= + (MaxBackends + max_prepared_xacts)); + } + + MySerializableXact = sxact; + + LWLockRelease(SerializableXactHashLock); + + /* Initialize the backend-local hash table of parent locks */ + Assert(LocalPredicateLockHash == NULL); + MemSet(&hash_ctl, 0, sizeof(hash_ctl)); + hash_ctl.keysize = sizeof(PREDICATELOCKTARGETTAG); + hash_ctl.entrysize = sizeof(LOCALPREDICATELOCK); + hash_ctl.hash = tag_hash; + LocalPredicateLockHash = hash_create("Local predicate lock", + max_predicate_locks_per_xact, + &hash_ctl, + HASH_ELEM | HASH_FUNCTION); + + return snapshot; +} + +/* + * Register the top level XID in SerializableXidHash. + * Also store it for easy reference in MySerializableXact. + */ +void +RegisterPredicateLockingXid(const TransactionId xid) +{ + SERIALIZABLEXIDTAG sxidtag; + SERIALIZABLEXID *sxid; + bool found; + + /* + * If we're not tracking predicate lock data for this transaction, we + * should ignore the request and return quickly. + */ + if (MySerializableXact == InvalidSerializableXact) + return; + + /* This should only be done once per transaction. */ + Assert(MySerializableXact->topXid == InvalidTransactionId); + + /* We should have a valid XID and be at the top level. */ + Assert(TransactionIdIsValid(xid)); + + MySerializableXact->topXid = xid; + + sxidtag.xid = xid; + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, + &sxidtag, + HASH_ENTER, &found); + if (!sxid) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"), + errhint("You might need to increase max_predicate_locks_per_transaction."))); + + Assert(!found); + + /* Initialize the structure. */ + sxid->myXact = (SERIALIZABLEXACT *) MySerializableXact; + LWLockRelease(SerializableXactHashLock); +} + + +/* + * Check whether there are any predicate locks held by any transaction + * for the page at the given block number. + * + * Note that the transaction may be completed but not yet subject to + * cleanup due to overlapping serializable transactions. This must + * return valid information regardless of transaction isolation level. + * + * Also note that this doesn't check for a conflicting relation lock, + * just a lock specifically on the given page. + * + * One use is to support proper behavior during GiST index vacuum. + */ +bool +PageIsPredicateLocked(const Relation relation, const BlockNumber blkno) +{ + PREDICATELOCKTARGETTAG targettag; + uint32 targettaghash; + LWLockId partitionLock; + PREDICATELOCKTARGET *target; + + SET_PREDICATELOCKTARGETTAG_PAGE(targettag, + relation->rd_node.dbNode, + relation->rd_id, + blkno); + + targettaghash = PredicateLockTargetTagHashCode(&targettag); + partitionLock = PredicateLockHashPartitionLock(targettaghash); + LWLockAcquire(partitionLock, LW_SHARED); + target = (PREDICATELOCKTARGET *) + hash_search_with_hash_value(PredicateLockTargetHash, + &targettag, targettaghash, + HASH_FIND, NULL); + LWLockRelease(partitionLock); + + return (target != NULL); +} + + +/* + * Check whether a particular lock is held by this transaction. + * + * Important note: this function may return false even if the lock is + * being held, because it uses the local lock table which is not + * updated if another transaction modifies our lock list (e.g. to + * split an index page). However, it will never return true if the + * lock is not held. We only use this function in circumstances where + * such false negatives are acceptable. + */ +static bool +PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag) +{ + LOCALPREDICATELOCK *lock; + + /* check local hash table */ + lock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash, + targettag, + HASH_FIND, NULL); + + if (!lock) + return false; + + /* + * Found entry in the table, but still need to check whether it's actually + * held -- it could just be a parent of some held lock. + */ + return lock->held; +} + +/* + * Return the parent lock tag in the lock hierarchy: the next coarser + * lock that covers the provided tag. + * + * Returns true and sets *parent to the parent tag if one exists, + * returns false if none exists. + */ +static bool +GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag, + PREDICATELOCKTARGETTAG *parent) +{ + switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag)) + { + case PREDLOCKTAG_RELATION: + /* relation locks have no parent lock */ + return false; + + case PREDLOCKTAG_PAGE: + /* parent lock is relation lock */ + SET_PREDICATELOCKTARGETTAG_RELATION(*parent, + GET_PREDICATELOCKTARGETTAG_DB(*tag), + GET_PREDICATELOCKTARGETTAG_RELATION(*tag)); + + return true; + + case PREDLOCKTAG_TUPLE: + /* parent lock is page lock */ + SET_PREDICATELOCKTARGETTAG_PAGE(*parent, + GET_PREDICATELOCKTARGETTAG_DB(*tag), + GET_PREDICATELOCKTARGETTAG_RELATION(*tag), + GET_PREDICATELOCKTARGETTAG_PAGE(*tag)); + return true; + } + + /* not reachable */ + Assert(false); + return false; +} + +/* + * Check whether the lock we are considering is already covered by a + * coarser lock for our transaction. + */ +static bool +CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag) +{ + PREDICATELOCKTARGETTAG targettag, + parenttag; + + targettag = *newtargettag; + + /* check parents iteratively until no more */ + while (GetParentPredicateLockTag(&targettag, &parenttag)) + { + targettag = parenttag; + if (PredicateLockExists(&targettag)) + return true; + } + + /* no more parents to check; lock is not covered */ + return false; +} + +/* + * Check whether both the list of related predicate locks and the pointer to + * a prior version of the row (if this is a tuple lock target) are empty for + * a predicate lock target, and remove the target if they are. + */ +static void +RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target, uint32 targettaghash) +{ + PREDICATELOCKTARGET *rmtarget; + PREDICATELOCKTARGET *next; + + Assert(LWLockHeldByMe(SerializablePredicateLockListLock)); + + /* Can't remove it until no locks at this target. */ + if (!SHMQueueEmpty(&target->predicateLocks)) + return; + + /* Can't remove it if there are locks for a prior row version. */ + LWLockAcquire(PredicateLockNextRowLinkLock, LW_EXCLUSIVE); + if (target->priorVersionOfRow != NULL) + { + LWLockRelease(PredicateLockNextRowLinkLock); + return; + } + + /* + * We are going to release this target, This requires that we let the + * next version of the row (if any) know that it's previous version is + * done. + * + * It might be that the link was all that was keeping the other target + * from cleanup, but we can't clean that up here -- LW locking is all + * wrong for that. We'll pass the HTAB in the general cleanup function to + * get rid of such "dead" targets. + */ + next = target->nextVersionOfRow; + if (next != NULL) + { + next->priorVersionOfRow = NULL; + if (SHMQueueEmpty(&next->predicateLocks)) + PredXact->NeedTargetLinkCleanup = true; + } + LWLockRelease(PredicateLockNextRowLinkLock); + + /* Actually remove the target. */ + rmtarget = hash_search_with_hash_value(PredicateLockTargetHash, + &target->tag, + targettaghash, + HASH_REMOVE, NULL); + Assert(rmtarget == target); +} + +/* + * Delete child target locks owned by this process. + * This implementation is assuming that the usage of each target tag field + * is uniform. No need to make this hard if we don't have to. + * + * We aren't acquiring lightweight locks for the predicate lock or lock + * target structures associated with this transaction unless we're going + * to modify them, because no other process is permitted to modify our + * locks. + */ +static void +DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag) +{ + SERIALIZABLEXACT *sxact; + PREDICATELOCK *predlock; + + LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); + sxact = (SERIALIZABLEXACT *) MySerializableXact; + predlock = (PREDICATELOCK *) + SHMQueueNext(&(sxact->predicateLocks), + &(sxact->predicateLocks), + offsetof(PREDICATELOCK, xactLink)); + while (predlock) + { + SHM_QUEUE *predlocksxactlink; + PREDICATELOCK *nextpredlock; + PREDICATELOCKTAG oldlocktag; + PREDICATELOCKTARGET *oldtarget; + PREDICATELOCKTARGETTAG oldtargettag; + + predlocksxactlink = &(predlock->xactLink); + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&(sxact->predicateLocks), + predlocksxactlink, + offsetof(PREDICATELOCK, xactLink)); + + oldlocktag = predlock->tag; + Assert(oldlocktag.myXact == sxact); + oldtarget = oldlocktag.myTarget; + oldtargettag = oldtarget->tag; + + if (TargetTagIsCoveredBy(oldtargettag, *newtargettag)) + { + uint32 oldtargettaghash; + LWLockId partitionLock; + PREDICATELOCK *rmpredlock; + + oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag); + partitionLock = PredicateLockHashPartitionLock(oldtargettaghash); + + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + + SHMQueueDelete(predlocksxactlink); + SHMQueueDelete(&(predlock->targetLink)); + rmpredlock = hash_search_with_hash_value + (PredicateLockHash, + &oldlocktag, + PredicateLockHashCodeFromTargetHashCode(&oldlocktag, + oldtargettaghash), + HASH_REMOVE, NULL); + Assert(rmpredlock == predlock); + + RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash); + + LWLockRelease(partitionLock); + + DecrementParentLocks(&oldtargettag); + } + + predlock = nextpredlock; + } + LWLockRelease(SerializablePredicateLockListLock); +} + +/* + * Returns the promotion threshold for a given predicate lock + * target. This is the number of descendant locks required to promote + * to the specified tag. Note that the threshold includes non-direct + * descendants, e.g. both tuples and pages for a relation lock. + * + * TODO SSI: We should do something more intelligent about what the + * thresholds are, either making it proportional to the number of + * tuples in a page & pages in a relation, or at least making it a + * GUC. Currently the threshold is 3 for a page lock, and + * max_predicate_locks_per_transaction/2 for a relation lock, chosen + * entirely arbitrarily (and without benchmarking). + */ +static int +PredicateLockPromotionThreshold(const PREDICATELOCKTARGETTAG *tag) +{ + switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag)) + { + case PREDLOCKTAG_RELATION: + return max_predicate_locks_per_xact / 2; + + case PREDLOCKTAG_PAGE: + return 3; + + case PREDLOCKTAG_TUPLE: + + /* + * not reachable: nothing is finer-granularity than a tuple, so we + * should never try to promote to it. + */ + Assert(false); + return 0; + } + + /* not reachable */ + Assert(false); + return 0; +} + +/* + * For all ancestors of a newly-acquired predicate lock, increment + * their child count in the parent hash table. If any of them have + * more descendants than their promotion threshold, acquire the + * coarsest such lock. + * + * Returns true if a parent lock was acquired and false otherwise. + */ +static bool +CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag) +{ + PREDICATELOCKTARGETTAG targettag, + nexttag, + promotiontag; + LOCALPREDICATELOCK *parentlock; + bool found, + promote; + + promote = false; + + targettag = *reqtag; + + /* check parents iteratively */ + while (GetParentPredicateLockTag(&targettag, &nexttag)) + { + targettag = nexttag; + parentlock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash, + &targettag, + HASH_ENTER, + &found); + if (!found) + { + parentlock->held = false; + parentlock->childLocks = 1; + } + else + parentlock->childLocks++; + + if (parentlock->childLocks >= + PredicateLockPromotionThreshold(&targettag)) + { + /* + * We should promote to this parent lock. Continue to check its + * ancestors, however, both to get their child counts right and to + * check whether we should just go ahead and promote to one of + * them. + */ + promotiontag = targettag; + promote = true; + } + } + + if (promote) + { + /* acquire coarsest ancestor eligible for promotion */ + PredicateLockAcquire(&promotiontag); + return true; + } + else + return false; +} + +/* + * When releasing a lock, decrement the child count on all ancestor + * locks. + * + * This is called only when releasing a lock via + * DeleteChildTargetLocks (i.e. when a lock becomes redundant because + * we've acquired its parent, possibly due to promotion) or when a new + * MVCC write lock makes the predicate lock unnecessary. There's no + * point in calling it when locks are released at transaction end, as + * this information is no longer needed. + */ +static void +DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag) +{ + PREDICATELOCKTARGETTAG parenttag, + nexttag; + + parenttag = *targettag; + + while (GetParentPredicateLockTag(&parenttag, &nexttag)) + { + uint32 targettaghash; + LOCALPREDICATELOCK *parentlock, + *rmlock; + + parenttag = nexttag; + targettaghash = PredicateLockTargetTagHashCode(&parenttag); + parentlock = (LOCALPREDICATELOCK *) + hash_search_with_hash_value(LocalPredicateLockHash, + &parenttag, targettaghash, + HASH_FIND, NULL); + + /* + * There's a small chance the parent lock doesn't exist in the lock + * table. This can happen if we prematurely removed it because an + * index split caused the child refcount to be off. + */ + if (parentlock == NULL) + continue; + + parentlock->childLocks--; + + /* + * Under similar circumstances the parent lock's refcount might be + * zero. This only happens if we're holding that lock (otherwise we + * would have removed the entry). + */ + if (parentlock->childLocks < 0) + { + Assert(parentlock->held); + parentlock->childLocks = 0; + } + + if ((parentlock->childLocks == 0) && (!parentlock->held)) + { + rmlock = (LOCALPREDICATELOCK *) + hash_search_with_hash_value(LocalPredicateLockHash, + &parenttag, targettaghash, + HASH_REMOVE, NULL); + Assert(rmlock == parentlock); + } + } +} + +/* + * Indicate that a predicate lock on the given target is held by the + * specified transaction. Has no effect if the lock is already held. + * + * This updates the lock table and the sxact's lock list, and creates + * the lock target if necessary, but does *not* do anything related to + * granularity promotion or the local lock table. See + * PredicateLockAcquire for that. + */ +static void +CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag, + uint32 targettaghash, + SERIALIZABLEXACT *sxact) +{ + PREDICATELOCKTARGET *target; + PREDICATELOCKTAG locktag; + PREDICATELOCK *lock; + LWLockId partitionLock; + bool found; + + partitionLock = PredicateLockHashPartitionLock(targettaghash); + + LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + + /* Make sure that the target is represented. */ + target = (PREDICATELOCKTARGET *) + hash_search_with_hash_value(PredicateLockTargetHash, + targettag, targettaghash, + HASH_ENTER, &found); + if (!target) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"), + errhint("You might need to increase max_predicate_locks_per_transaction."))); + if (!found) + { + SHMQueueInit(&(target->predicateLocks)); + target->priorVersionOfRow = NULL; + target->nextVersionOfRow = NULL; + } + + /* We've got the sxact and target, make sure they're joined. */ + locktag.myTarget = target; + locktag.myXact = sxact; + lock = (PREDICATELOCK *) + hash_search_with_hash_value(PredicateLockHash, &locktag, + PredicateLockHashCodeFromTargetHashCode(&locktag, targettaghash), + HASH_ENTER, &found); + if (!lock) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"), + errhint("You might need to increase max_predicate_locks_per_transaction."))); + + if (!found) + { + SHMQueueInsertBefore(&(target->predicateLocks), &(lock->targetLink)); + SHMQueueInsertBefore(&(sxact->predicateLocks), + &(lock->xactLink)); + lock->commitSeqNo = 0; + } + + LWLockRelease(partitionLock); + LWLockRelease(SerializablePredicateLockListLock); +} + +/* + * Acquire a predicate lock on the specified target for the current + * connection if not already held. This updates the local lock table + * and uses it to implement granularity promotion. It will consolidate + * multiple locks into a coarser lock if warranted, and will release + * any finer-grained locks covered by the new one. + */ +static void +PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag) +{ + uint32 targettaghash; + bool found; + LOCALPREDICATELOCK *locallock; + + /* Do we have the lock already, or a covering lock? */ + if (PredicateLockExists(targettag)) + return; + + if (CoarserLockCovers(targettag)) + return; + + /* the same hash and LW lock apply to the lock target and the local lock. */ + targettaghash = PredicateLockTargetTagHashCode(targettag); + + /* Acquire lock in local table */ + locallock = (LOCALPREDICATELOCK *) + hash_search_with_hash_value(LocalPredicateLockHash, + targettag, targettaghash, + HASH_ENTER, &found); + /* We should not hold the lock (but its entry might still exist) */ + Assert(!found || !locallock->held); + locallock->held = true; + if (!found) + locallock->childLocks = 0; + + /* Actually create the lock */ + CreatePredicateLock(targettag, targettaghash, + (SERIALIZABLEXACT *) MySerializableXact); + + /* + * Lock has been acquired. Check whether it should be promoted to a + * coarser granularity, or whether there are finer-granularity locks to + * clean up. + */ + if (CheckAndPromotePredicateLockRequest(targettag)) + { + /* + * Lock request was promoted to a coarser-granularity lock, and that + * lock was acquired. It will delete this lock and any of its + * children, so we're done. + */ + } + else + { + /* Clean up any finer-granularity locks */ + if (GET_PREDICATELOCKTARGETTAG_TYPE(*targettag) != PREDLOCKTAG_TUPLE) + DeleteChildTargetLocks(targettag); + } +} + + +/* + * PredicateLockRelation + * + * Gets a predicate lock at the relation level. + * Skip if not in full serializable transaction isolation level. + * Skip if this is a temporary table. + * Clear any finer-grained predicate locks this session has on the relation. + */ +void +PredicateLockRelation(const Relation relation) +{ + PREDICATELOCKTARGETTAG tag; + + if (SkipSerialization(relation)) + return; + + SET_PREDICATELOCKTARGETTAG_RELATION(tag, + relation->rd_node.dbNode, + relation->rd_id); + PredicateLockAcquire(&tag); +} + +/* + * PredicateLockPage + * + * Gets a predicate lock at the page level. + * Skip if not in full serializable transaction isolation level. + * Skip if this is a temporary table. + * Skip if a coarser predicate lock already covers this page. + * Clear any finer-grained predicate locks this session has on the relation. + */ +void +PredicateLockPage(const Relation relation, const BlockNumber blkno) +{ + PREDICATELOCKTARGETTAG tag; + + if (SkipSerialization(relation)) + return; + + SET_PREDICATELOCKTARGETTAG_PAGE(tag, + relation->rd_node.dbNode, + relation->rd_id, + blkno); + PredicateLockAcquire(&tag); +} + +/* + * PredicateLockTuple + * + * Gets a predicate lock at the tuple level. + * Skip if not in full serializable transaction isolation level. + * Skip if this is a temporary table. + */ +void +PredicateLockTuple(const Relation relation, const HeapTuple tuple) +{ + PREDICATELOCKTARGETTAG tag; + ItemPointer tid; + + if (SkipSerialization(relation)) + return; + + /* + * If it's a heap tuple, return if this xact wrote it. + */ + if (relation->rd_index == NULL) + { + TransactionId myxid = GetTopTransactionIdIfAny(); + + if (TransactionIdIsValid(myxid)) + { + TransactionId xid = HeapTupleHeaderGetXmin(tuple->t_data); + + if (TransactionIdFollowsOrEquals(xid, TransactionXmin)) + { + xid = SubTransGetTopmostTransaction(xid); + if (TransactionIdEquals(xid, myxid)) + { + /* We wrote it; we already have a write lock. */ + return; + } + } + } + } + + /* + * Do quick-but-not-definitive test for a relation lock first. This will + * never cause a return when the relation is *not* locked, but will + * occasionally let the check continue when there really *is* a relation + * level lock. + */ + SET_PREDICATELOCKTARGETTAG_RELATION(tag, + relation->rd_node.dbNode, + relation->rd_id); + if (PredicateLockExists(&tag)) + return; + + tid = &(tuple->t_self); + SET_PREDICATELOCKTARGETTAG_TUPLE(tag, + relation->rd_node.dbNode, + relation->rd_id, + ItemPointerGetBlockNumber(tid), + ItemPointerGetOffsetNumber(tid)); + PredicateLockAcquire(&tag); +} + +/* + * If the old tuple has any predicate locks, create a lock target for the + * new tuple and point them at each other. Conflict detection needs to + * look for locks against prior versions of the row. + */ +void +PredicateLockTupleRowVersionLink(const Relation relation, + const HeapTuple oldTuple, + const HeapTuple newTuple) +{ + PREDICATELOCKTARGETTAG oldtargettag; + PREDICATELOCKTARGETTAG newtargettag; + PREDICATELOCKTARGET *oldtarget; + PREDICATELOCKTARGET *newtarget; + PREDICATELOCKTARGET *next; + uint32 oldtargettaghash; + LWLockId oldpartitionLock; + uint32 newtargettaghash; + LWLockId newpartitionLock; + bool found; + + SET_PREDICATELOCKTARGETTAG_TUPLE(oldtargettag, + relation->rd_node.dbNode, + relation->rd_id, + ItemPointerGetBlockNumber(&(oldTuple->t_self)), + ItemPointerGetOffsetNumber(&(oldTuple->t_self))); + oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag); + oldpartitionLock = PredicateLockHashPartitionLock(oldtargettaghash); + + SET_PREDICATELOCKTARGETTAG_TUPLE(newtargettag, + relation->rd_node.dbNode, + relation->rd_id, + ItemPointerGetBlockNumber(&(newTuple->t_self)), + ItemPointerGetOffsetNumber(&(newTuple->t_self))); + newtargettaghash = PredicateLockTargetTagHashCode(&newtargettag); + newpartitionLock = PredicateLockHashPartitionLock(newtargettaghash); + + /* Lock lower numbered partition first. */ + if (oldpartitionLock < newpartitionLock) + { + LWLockAcquire(oldpartitionLock, LW_SHARED); + LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); + } + else if (newpartitionLock < oldpartitionLock) + { + LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); + LWLockAcquire(oldpartitionLock, LW_SHARED); + } + else + LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); + + oldtarget = (PREDICATELOCKTARGET *) + hash_search_with_hash_value(PredicateLockTargetHash, + &oldtargettag, oldtargettaghash, + HASH_FIND, NULL); + + /* Only need to link if there is an old target already. */ + if (oldtarget) + { + LWLockAcquire(PredicateLockNextRowLinkLock, LW_EXCLUSIVE); + + /* Guard against stale pointers from rollback. */ + next = oldtarget->nextVersionOfRow; + if (next != NULL) + { + next->priorVersionOfRow = NULL; + oldtarget->nextVersionOfRow = NULL; + } + + /* Find or create the new target, and link old and new. */ + newtarget = (PREDICATELOCKTARGET *) + hash_search_with_hash_value(PredicateLockTargetHash, + &newtargettag, newtargettaghash, + HASH_ENTER, &found); + if (!newtarget) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"), + errhint("You might need to increase max_predicate_locks_per_transaction."))); + if (!found) + { + SHMQueueInit(&(newtarget->predicateLocks)); + newtarget->nextVersionOfRow = NULL; + } + else + Assert(newtarget->priorVersionOfRow == NULL); + + newtarget->priorVersionOfRow = oldtarget; + oldtarget->nextVersionOfRow = newtarget; + + LWLockRelease(PredicateLockNextRowLinkLock); + } + + /* Release lower number partition last. */ + if (oldpartitionLock < newpartitionLock) + { + LWLockRelease(newpartitionLock); + LWLockRelease(oldpartitionLock); + } + else if (newpartitionLock < oldpartitionLock) + { + LWLockRelease(oldpartitionLock); + LWLockRelease(newpartitionLock); + } + else + LWLockRelease(newpartitionLock); +} + + +/* + * DeleteLockTarget + * + * Remove a predicate lock target along with any locks held for it. + * + * Caller must hold SerializablePredicateLockListLock and the + * appropriate hash partition lock for the target. + */ +static void +DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash) +{ + PREDICATELOCK *predlock; + SHM_QUEUE *predlocktargetlink; + PREDICATELOCK *nextpredlock; + bool found; + + Assert(LWLockHeldByMe(SerializablePredicateLockListLock)); + Assert(LWLockHeldByMe(PredicateLockHashPartitionLock(targettaghash))); + + predlock = (PREDICATELOCK *) + SHMQueueNext(&(target->predicateLocks), + &(target->predicateLocks), + offsetof(PREDICATELOCK, targetLink)); + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + while (predlock) + { + predlocktargetlink = &(predlock->targetLink); + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&(target->predicateLocks), + predlocktargetlink, + offsetof(PREDICATELOCK, targetLink)); + + SHMQueueDelete(&(predlock->xactLink)); + SHMQueueDelete(&(predlock->targetLink)); + + hash_search_with_hash_value + (PredicateLockHash, + &predlock->tag, + PredicateLockHashCodeFromTargetHashCode(&predlock->tag, + targettaghash), + HASH_REMOVE, &found); + Assert(found); + + predlock = nextpredlock; + } + LWLockRelease(SerializableXactHashLock); + + /* Remove the target itself, if possible. */ + RemoveTargetIfNoLongerUsed(target, targettaghash); +} + + +/* + * TransferPredicateLocksToNewTarget + * + * Move or copy all the predicate locks for a lock target, for use by + * index page splits/combines and other things that create or replace + * lock targets. If 'removeOld' is true, the old locks and the target + * will be removed. + * + * Returns true on success, or false if we ran out of shared memory to + * allocate the new target or locks. Guaranteed to always succeed if + * removeOld is set (by using the reserved entry in + * PredicateLockTargetHash for scratch space). + * + * Caller must hold SerializablePredicateLockListLock. + */ +static bool +TransferPredicateLocksToNewTarget(const PREDICATELOCKTARGETTAG oldtargettag, + const PREDICATELOCKTARGETTAG newtargettag, + bool removeOld) +{ + uint32 oldtargettaghash; + LWLockId oldpartitionLock; + PREDICATELOCKTARGET *oldtarget; + uint32 newtargettaghash; + LWLockId newpartitionLock; + bool found; + bool outOfShmem = false; + uint32 reservedtargettaghash; + LWLockId reservedpartitionLock; + + + Assert(LWLockHeldByMe(SerializablePredicateLockListLock)); + + oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag); + newtargettaghash = PredicateLockTargetTagHashCode(&newtargettag); + oldpartitionLock = PredicateLockHashPartitionLock(oldtargettaghash); + newpartitionLock = PredicateLockHashPartitionLock(newtargettaghash); + + reservedtargettaghash = 0; /* Quiet compiler warnings. */ + reservedpartitionLock = 0; /* Quiet compiler warnings. */ + + if (removeOld) + { + /* + * Remove the reserved entry to give us scratch space, so we know + * we'll be able to create the new lock target. + */ + reservedtargettaghash = PredicateLockTargetTagHashCode(&ReservedTargetTag); + reservedpartitionLock = PredicateLockHashPartitionLock(reservedtargettaghash); + LWLockAcquire(reservedpartitionLock, LW_EXCLUSIVE); + hash_search_with_hash_value(PredicateLockTargetHash, + &ReservedTargetTag, + reservedtargettaghash, + HASH_REMOVE, &found); + Assert(found); + LWLockRelease(reservedpartitionLock); + } + + /* + * We must get the partition locks in ascending sequence to avoid + * deadlocks. If old and new partitions are the same, we must request the + * lock only once. + */ + if (oldpartitionLock < newpartitionLock) + { + LWLockAcquire(oldpartitionLock, + (removeOld ? LW_EXCLUSIVE : LW_SHARED)); + LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); + } + else if (oldpartitionLock > newpartitionLock) + { + LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); + LWLockAcquire(oldpartitionLock, + (removeOld ? LW_EXCLUSIVE : LW_SHARED)); + } + else + LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); + + /* + * Look for the old target. If not found, that's OK; no predicate locks + * are affected, so we can just clean up and return. If it does exist, + * walk its list of predicate locks and move or copy them to the new + * target. + */ + oldtarget = hash_search_with_hash_value(PredicateLockTargetHash, + &oldtargettag, + oldtargettaghash, + HASH_FIND, NULL); + + if (oldtarget) + { + PREDICATELOCKTARGET *newtarget; + PREDICATELOCK *oldpredlock; + PREDICATELOCKTAG newpredlocktag; + + newtarget = hash_search_with_hash_value(PredicateLockTargetHash, + &newtargettag, + newtargettaghash, + HASH_ENTER_NULL, &found); + + if (!newtarget) + { + /* Failed to allocate due to insufficient shmem */ + outOfShmem = true; + goto exit; + } + + /* If we created a new entry, initialize it */ + if (!found) + { + SHMQueueInit(&(newtarget->predicateLocks)); + newpredlocktag.myTarget = newtarget; + } + + oldpredlock = (PREDICATELOCK *) + SHMQueueNext(&(oldtarget->predicateLocks), + &(oldtarget->predicateLocks), + offsetof(PREDICATELOCK, targetLink)); + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + while (oldpredlock) + { + SHM_QUEUE *predlocktargetlink; + PREDICATELOCK *nextpredlock; + PREDICATELOCK *newpredlock; + + predlocktargetlink = &(oldpredlock->targetLink); + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&(oldtarget->predicateLocks), + predlocktargetlink, + offsetof(PREDICATELOCK, targetLink)); + newpredlocktag.myXact = oldpredlock->tag.myXact; + + if (removeOld) + { + SHMQueueDelete(&(oldpredlock->xactLink)); + SHMQueueDelete(&(oldpredlock->targetLink)); + + hash_search_with_hash_value + (PredicateLockHash, + &oldpredlock->tag, + PredicateLockHashCodeFromTargetHashCode(&oldpredlock->tag, + oldtargettaghash), + HASH_REMOVE, &found); + Assert(found); + } + + + newpredlock = (PREDICATELOCK *) + hash_search_with_hash_value + (PredicateLockHash, + &newpredlocktag, + PredicateLockHashCodeFromTargetHashCode(&newpredlocktag, + newtargettaghash), + HASH_ENTER_NULL, &found); + if (!newpredlock) + { + /* Out of shared memory. Undo what we've done so far. */ + LWLockRelease(SerializableXactHashLock); + DeleteLockTarget(newtarget, newtargettaghash); + outOfShmem = true; + goto exit; + } + SHMQueueInsertBefore(&(newtarget->predicateLocks), + &(newpredlock->targetLink)); + SHMQueueInsertBefore(&(newpredlocktag.myXact->predicateLocks), + &(newpredlock->xactLink)); + + oldpredlock = nextpredlock; + } + LWLockRelease(SerializableXactHashLock); + + if (removeOld) + { + Assert(SHMQueueEmpty(&oldtarget->predicateLocks)); + RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash); + } + } + + +exit: + /* Release partition locks in reverse order of acquisition. */ + if (oldpartitionLock < newpartitionLock) + { + LWLockRelease(newpartitionLock); + LWLockRelease(oldpartitionLock); + } + else if (oldpartitionLock > newpartitionLock) + { + LWLockRelease(oldpartitionLock); + LWLockRelease(newpartitionLock); + } + else + LWLockRelease(newpartitionLock); + + if (removeOld) + { + /* We shouldn't run out of memory if we're moving locks */ + Assert(!outOfShmem); + + /* Put the reserved entry back */ + LWLockAcquire(reservedpartitionLock, LW_EXCLUSIVE); + hash_search_with_hash_value(PredicateLockTargetHash, + &ReservedTargetTag, + reservedtargettaghash, + HASH_ENTER, &found); + Assert(!found); + LWLockRelease(reservedpartitionLock); + } + + return !outOfShmem; +} + + +/* + * PredicateLockPageSplit + * + * Copies any predicate locks for the old page to the new page. + * Skip if this is a temporary table or toast table. + * + * NOTE: A page split (or overflow) affects all serializable transactions, + * even if it occurs in the context of another transaction isolation level. + * + * NOTE: This currently leaves the local copy of the locks without + * information on the new lock which is in shared memory. This could cause + * problems if enough page splits occur on locked pages without the processes + * which hold the locks getting in and noticing. + */ +void +PredicateLockPageSplit(const Relation relation, const BlockNumber oldblkno, + const BlockNumber newblkno) +{ + PREDICATELOCKTARGETTAG oldtargettag; + PREDICATELOCKTARGETTAG newtargettag; + bool success; + + if (SkipSplitTracking(relation)) + return; + + Assert(oldblkno != newblkno); + Assert(BlockNumberIsValid(oldblkno)); + Assert(BlockNumberIsValid(newblkno)); + + SET_PREDICATELOCKTARGETTAG_PAGE(oldtargettag, + relation->rd_node.dbNode, + relation->rd_id, + oldblkno); + SET_PREDICATELOCKTARGETTAG_PAGE(newtargettag, + relation->rd_node.dbNode, + relation->rd_id, + newblkno); + + LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE); + + /* + * Try copying the locks over to the new page's tag, creating it if + * necessary. + */ + success = TransferPredicateLocksToNewTarget(oldtargettag, + newtargettag, + false); + + if (!success) + { + /* + * No more predicate lock entries are available. Failure isn't an + * option here, so promote the page lock to a relation lock. + */ + + /* Get the parent relation lock's lock tag */ + success = GetParentPredicateLockTag(&oldtargettag, + &newtargettag); + Assert(success); + + /* Move the locks to the parent. This shouldn't fail. */ + success = TransferPredicateLocksToNewTarget(oldtargettag, + newtargettag, + true); + Assert(success); + } + + LWLockRelease(SerializablePredicateLockListLock); +} + +/* + * PredicateLockPageCombine + * + * Combines predicate locks for two existing pages. + * Skip if this is a temporary table or toast table. + * + * NOTE: A page combine affects all serializable transactions, even if it + * occurs in the context of another transaction isolation level. + */ +void +PredicateLockPageCombine(const Relation relation, const BlockNumber oldblkno, + const BlockNumber newblkno) +{ + PREDICATELOCKTARGETTAG oldtargettag; + PREDICATELOCKTARGETTAG newtargettag; + bool success; + + + if (SkipSplitTracking(relation)) + return; + + Assert(oldblkno != newblkno); + Assert(BlockNumberIsValid(oldblkno)); + Assert(BlockNumberIsValid(newblkno)); + + SET_PREDICATELOCKTARGETTAG_PAGE(oldtargettag, + relation->rd_node.dbNode, + relation->rd_id, + oldblkno); + SET_PREDICATELOCKTARGETTAG_PAGE(newtargettag, + relation->rd_node.dbNode, + relation->rd_id, + newblkno); + + LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE); + + /* Move the locks. This shouldn't fail. */ + success = TransferPredicateLocksToNewTarget(oldtargettag, + newtargettag, + true); + Assert(success); + + LWLockRelease(SerializablePredicateLockListLock); +} + +/* + * Walk the hash table and find the new xmin. + */ +static void +SetNewSxactGlobalXmin(void) +{ + SERIALIZABLEXACT *sxact; + + Assert(LWLockHeldByMe(SerializableXactHashLock)); + + PredXact->SxactGlobalXmin = InvalidTransactionId; + PredXact->SxactGlobalXminCount = 0; + + for (sxact = FirstPredXact(); sxact != NULL; sxact = NextPredXact(sxact)) + { + if (!SxactIsRolledBack(sxact) + && !SxactIsCommitted(sxact) + && sxact != OldCommittedSxact) + { + Assert(sxact->xmin != InvalidTransactionId); + if (!TransactionIdIsValid(PredXact->SxactGlobalXmin) + || TransactionIdPrecedes(sxact->xmin, + PredXact->SxactGlobalXmin)) + { + PredXact->SxactGlobalXmin = sxact->xmin; + PredXact->SxactGlobalXminCount = 1; + } + else if (TransactionIdEquals(sxact->xmin, + PredXact->SxactGlobalXmin)) + PredXact->SxactGlobalXminCount++; + } + } + + OldSerXidSetActiveSerXmin(PredXact->SxactGlobalXmin); +} + +/* + * ReleasePredicateLocks + * + * Releases predicate locks based on completion of the current transaction, + * whether committed or rolled back. It can also be called for a read only + * transaction when it becomes impossible for the transaction to become + * part of a dangerous structure. + * + * We do nothing unless this is a serializable transaction. + * + * This method must ensure that shared memory hash tables are cleaned + * up in some relatively timely fashion. + * + * If this transaction is committing and is holding any predicate locks, + * it must be added to a list of completed serializable transaction still + * holding locks. + */ +void +ReleasePredicateLocks(const bool isCommit) +{ + bool needToClear; + RWConflict conflict, + nextConflict, + possibleUnsafeConflict; + SERIALIZABLEXACT *roXact; + + /* + * We can't trust XactReadOnly here, because a transaction which started + * as READ WRITE can show as READ ONLY later, e.g., within + * substransactions. We want to flag a transaction as READ ONLY if it + * commits without writing so that de facto READ ONLY transactions get the + * benefit of some RO optimizations, so we will use this local variable to + * get some cleanup logic right which is based on whether the transaction + * was declared READ ONLY at the top level. + */ + bool topLevelIsDeclaredReadOnly; + + if (MySerializableXact == InvalidSerializableXact) + { + Assert(LocalPredicateLockHash == NULL); + return; + } + + Assert(!isCommit || SxactIsPrepared(MySerializableXact)); + Assert(!SxactIsRolledBack(MySerializableXact)); + Assert(!SxactIsCommitted(MySerializableXact)); + + /* may not be serializable during COMMIT/ROLLBACK PREPARED */ + if (MySerializableXact->pid != 0) + Assert(IsolationIsSerializable()); + + /* We'd better not already be on the cleanup list. */ + Assert(!SxactIsOnFinishedList((SERIALIZABLEXACT *) MySerializableXact)); + + topLevelIsDeclaredReadOnly = SxactIsReadOnly(MySerializableXact); + + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + + /* + * We don't hold a lock here, assuming that TransactionId is atomic! + * + * If this value is changing, we don't care that much whether we get the + * old or new value -- it is just used to determine how far + * GlobalSerizableXmin must advance before this transaction can be cleaned + * fully cleaned up. The worst that could happen is we wait for ome more + * transaction to complete before freeing some RAM; correctness of visible + * behavior is not affected. + */ + MySerializableXact->finishedBefore = ShmemVariableCache->nextXid; + + /* + * If it's not a commit it's a rollback, and we can clear our locks + * immediately. + */ + if (isCommit) + { + MySerializableXact->flags |= SXACT_FLAG_COMMITTED; + MySerializableXact->commitSeqNo = ++(PredXact->LastSxactCommitSeqNo); + /* Recognize implicit read-only transaction (commit without write). */ + if (!(MySerializableXact->flags & SXACT_FLAG_DID_WRITE)) + MySerializableXact->flags |= SXACT_FLAG_READ_ONLY; + } + else + { + MySerializableXact->flags |= SXACT_FLAG_ROLLED_BACK; + } + + if (!topLevelIsDeclaredReadOnly) + { + Assert(PredXact->WritableSxactCount > 0); + if (--(PredXact->WritableSxactCount) == 0) + { + /* + * Release predicate locks and rw-conflicts in for all committed + * transactions. There are no longer any transactions which might + * conflict with the locks and no chance for new transactions to + * overlap. Similarly, existing conflicts in can't cause pivots, + * and any conflicts in which could have completed a dangerous + * structure would already have caused a rollback, so any + * remaining ones must be benign. + */ + PredXact->CanPartialClearThrough = PredXact->LastSxactCommitSeqNo; + } + } + else + { + /* + * Read-only transactions: clear the list of transactions that might + * make us unsafe. Note that we use 'inLink' for the iteration as + * opposed to 'outLink' for the r/w xacts. + */ + possibleUnsafeConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, + (SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, + offsetof(RWConflictData, inLink)); + while (possibleUnsafeConflict) + { + nextConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, + &possibleUnsafeConflict->inLink, + offsetof(RWConflictData, inLink)); + + Assert(!SxactIsReadOnly(possibleUnsafeConflict->sxactOut)); + Assert(MySerializableXact == possibleUnsafeConflict->sxactIn); + + ReleaseRWConflict(possibleUnsafeConflict); + + possibleUnsafeConflict = nextConflict; + } + } + + /* Check for conflict out to old committed transactions. */ + if (isCommit + && !SxactIsReadOnly(MySerializableXact) + && SxactHasSummaryConflictOut(MySerializableXact)) + { + MySerializableXact->SeqNo.earliestOutConflictCommit = + FirstNormalSerCommitSeqNo; + MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT; + } + + /* + * Release all outConflicts to committed transactions. If we're rolling + * back clear them all. Set SXACT_FLAG_CONFLICT_OUT if any point to + * previously committed transactions. + */ + conflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->outConflicts, + (SHM_QUEUE *) &MySerializableXact->outConflicts, + offsetof(RWConflictData, outLink)); + while (conflict) + { + nextConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->outConflicts, + &conflict->outLink, + offsetof(RWConflictData, outLink)); + + if (isCommit + && !SxactIsReadOnly(MySerializableXact) + && SxactIsCommitted(conflict->sxactIn)) + { + if ((MySerializableXact->flags & SXACT_FLAG_CONFLICT_OUT) == 0 + || conflict->sxactIn->commitSeqNo < MySerializableXact->SeqNo.earliestOutConflictCommit) + MySerializableXact->SeqNo.earliestOutConflictCommit = conflict->sxactIn->commitSeqNo; + MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT; + } + + if (!isCommit + || SxactIsCommitted(conflict->sxactIn) + || (conflict->sxactIn->SeqNo.lastCommitBeforeSnapshot >= PredXact->LastSxactCommitSeqNo)) + ReleaseRWConflict(conflict); + + conflict = nextConflict; + } + + /* + * Release all inConflicts from committed and read-only transactions. If + * we're rolling back, clear them all. + */ + conflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, + (SHM_QUEUE *) &MySerializableXact->inConflicts, + offsetof(RWConflictData, inLink)); + while (conflict) + { + nextConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, + &conflict->inLink, + offsetof(RWConflictData, inLink)); + + if (!isCommit + || SxactIsCommitted(conflict->sxactOut) + || SxactIsReadOnly(conflict->sxactOut)) + ReleaseRWConflict(conflict); + + conflict = nextConflict; + } + + if (!topLevelIsDeclaredReadOnly) + { + /* + * Remove ourselves from the list of possible conflicts for concurrent + * READ ONLY transactions, flagging them as unsafe if we have a + * conflict out. If any are waiting DEFERRABLE transactions, wake them + * up if they are known safe or known unsafe. + */ + possibleUnsafeConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, + (SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, + offsetof(RWConflictData, outLink)); + while (possibleUnsafeConflict) + { + nextConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, + &possibleUnsafeConflict->outLink, + offsetof(RWConflictData, outLink)); + + roXact = possibleUnsafeConflict->sxactIn; + Assert(MySerializableXact == possibleUnsafeConflict->sxactOut); + Assert(SxactIsReadOnly(roXact)); + + /* Mark conflicted if necessary. */ + if (isCommit + && (MySerializableXact->flags & SXACT_FLAG_DID_WRITE) + && SxactHasConflictOut(MySerializableXact) + && (MySerializableXact->SeqNo.earliestOutConflictCommit + <= roXact->SeqNo.lastCommitBeforeSnapshot)) + { + /* + * This releases possibleUnsafeConflict (as well as all other + * possible conflicts for roXact) + */ + FlagSxactUnsafe(roXact); + } + else + { + ReleaseRWConflict(possibleUnsafeConflict); + + /* + * If we were the last possible conflict, flag it safe. The + * transaction can now safely release its predicate locks (but + * that transaction's backend has to do that itself). + */ + if (SHMQueueEmpty(&roXact->possibleUnsafeConflicts)) + roXact->flags |= SXACT_FLAG_RO_SAFE; + } + + /* + * Wake up the process for a waiting DEFERRABLE transaction if we + * now know it's either safe or conflicted. + */ + if (SxactIsDeferrableWaiting(roXact) && + (SxactIsROUnsafe(roXact) || SxactIsROSafe(roXact))) + ProcSendSignal(roXact->pid); + + possibleUnsafeConflict = nextConflict; + } + } + + /* + * Check whether it's time to clean up old transactions. This can only be + * done when the last serializable transaction with the oldest xmin among + * serializable transactions completes. We then find the "new oldest" + * xmin and purge any transactions which finished before this transaction + * was launched. + */ + needToClear = false; + if (TransactionIdEquals(MySerializableXact->xmin, PredXact->SxactGlobalXmin)) + { + Assert(PredXact->SxactGlobalXminCount > 0); + if (--(PredXact->SxactGlobalXminCount) == 0) + { + SetNewSxactGlobalXmin(); + needToClear = true; + } + } + + LWLockRelease(SerializableXactHashLock); + + LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); + + /* Add this to the list of transactions to check for later cleanup. */ + if (isCommit) + SHMQueueInsertBefore(FinishedSerializableTransactions, + (SHM_QUEUE *) &(MySerializableXact->finishedLink)); + + if (!isCommit) + ReleaseOneSerializableXact((SERIALIZABLEXACT *) MySerializableXact, + false, false); + + LWLockRelease(SerializableFinishedListLock); + + if (needToClear) + ClearOldPredicateLocks(); + + MySerializableXact = InvalidSerializableXact; + + /* Delete per-transaction lock table */ + if (LocalPredicateLockHash != NULL) + { + hash_destroy(LocalPredicateLockHash); + LocalPredicateLockHash = NULL; + } +} + +/* + * ReleasePredicateLocksIfROSafe + * Check if the current transaction is read only and operating on + * a safe snapshot. If so, release predicate locks and return + * true. + * + * A transaction is flagged as RO_SAFE if all concurrent R/W + * transactions commit without having conflicts out to an earlier + * snapshot, thus ensuring that no conflicts are possible for this + * transaction. Thus, we call this function as part of the + * SkipSerialization check on all public interface methods. + */ +static bool +ReleasePredicateLocksIfROSafe(void) +{ + if (SxactIsROSafe(MySerializableXact)) + { + ReleasePredicateLocks(false); + return true; + } + else + return false; +} + +/* + * Clear old predicate locks. + */ +static void +ClearOldPredicateLocks(void) +{ + SERIALIZABLEXACT *finishedSxact; + PREDICATELOCK *predlock; + int i; + HASH_SEQ_STATUS seqstat; + PREDICATELOCKTARGET *locktarget; + + LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); + finishedSxact = (SERIALIZABLEXACT *) + SHMQueueNext(FinishedSerializableTransactions, + FinishedSerializableTransactions, + offsetof(SERIALIZABLEXACT, finishedLink)); + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + while (finishedSxact) + { + SERIALIZABLEXACT *nextSxact; + + nextSxact = (SERIALIZABLEXACT *) + SHMQueueNext(FinishedSerializableTransactions, + &(finishedSxact->finishedLink), + offsetof(SERIALIZABLEXACT, finishedLink)); + if (!TransactionIdIsValid(PredXact->SxactGlobalXmin) + || TransactionIdPrecedesOrEquals(finishedSxact->finishedBefore, + PredXact->SxactGlobalXmin)) + { + LWLockRelease(SerializableXactHashLock); + SHMQueueDelete(&(finishedSxact->finishedLink)); + ReleaseOneSerializableXact(finishedSxact, false, false); + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + } + else if (finishedSxact->commitSeqNo > PredXact->HavePartialClearedThrough + && finishedSxact->commitSeqNo <= PredXact->CanPartialClearThrough) + { + LWLockRelease(SerializableXactHashLock); + ReleaseOneSerializableXact(finishedSxact, + !SxactIsReadOnly(finishedSxact), + false); + PredXact->HavePartialClearedThrough = finishedSxact->commitSeqNo; + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + } + else + break; + finishedSxact = nextSxact; + } + LWLockRelease(SerializableXactHashLock); + + /* + * Loop through predicate locks on dummy transaction for summarized data. + */ + predlock = (PREDICATELOCK *) + SHMQueueNext(&OldCommittedSxact->predicateLocks, + &OldCommittedSxact->predicateLocks, + offsetof(PREDICATELOCK, xactLink)); + LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); + while (predlock) + { + PREDICATELOCK *nextpredlock; + bool canDoPartialCleanup; + + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&OldCommittedSxact->predicateLocks, + &predlock->xactLink, + offsetof(PREDICATELOCK, xactLink)); + + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + canDoPartialCleanup = (predlock->commitSeqNo <= PredXact->CanPartialClearThrough); + LWLockRelease(SerializableXactHashLock); + + if (canDoPartialCleanup) + { + PREDICATELOCKTAG tag; + SHM_QUEUE *targetLink; + PREDICATELOCKTARGET *target; + PREDICATELOCKTARGETTAG targettag; + uint32 targettaghash; + LWLockId partitionLock; + + tag = predlock->tag; + targetLink = &(predlock->targetLink); + target = tag.myTarget; + targettag = target->tag; + targettaghash = PredicateLockTargetTagHashCode(&targettag); + partitionLock = PredicateLockHashPartitionLock(targettaghash); + + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + + SHMQueueDelete(targetLink); + SHMQueueDelete(&(predlock->xactLink)); + + hash_search_with_hash_value(PredicateLockHash, &tag, + PredicateLockHashCodeFromTargetHashCode(&tag, + targettaghash), + HASH_REMOVE, NULL); + RemoveTargetIfNoLongerUsed(target, targettaghash); + + LWLockRelease(partitionLock); + } + + predlock = nextpredlock; + } + + LWLockRelease(SerializablePredicateLockListLock); + LWLockRelease(SerializableFinishedListLock); + + if (!PredXact->NeedTargetLinkCleanup) + return; + + /* + * Clean up any targets which were disconnected from a prior version with + * no predicate locks attached. + */ + for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++) + LWLockAcquire(FirstPredicateLockMgrLock + i, LW_EXCLUSIVE); + LWLockAcquire(PredicateLockNextRowLinkLock, LW_SHARED); + + hash_seq_init(&seqstat, PredicateLockTargetHash); + while ((locktarget = (PREDICATELOCKTARGET *) hash_seq_search(&seqstat))) + { + if (SHMQueueEmpty(&locktarget->predicateLocks) + && locktarget->priorVersionOfRow == NULL + && locktarget->nextVersionOfRow == NULL) + { + hash_search(PredicateLockTargetHash, &locktarget->tag, + HASH_REMOVE, NULL); + } + } + + PredXact->NeedTargetLinkCleanup = false; + + LWLockRelease(PredicateLockNextRowLinkLock); + for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--) + LWLockRelease(FirstPredicateLockMgrLock + i); +} + +/* + * This is the normal way to delete anything from any of the predicate + * locking hash tables. Given a transaction which we know can be deleted: + * delete all predicate locks held by that transaction and any predicate + * lock targets which are now unreferenced by a lock; delete all conflicts + * for the transaction; delete all xid values for the transaction; then + * delete the transaction. + * + * When the partial flag is set, we can release all predicate locks and + * out-conflict information -- we've established that there are no longer + * any overlapping read write transactions for which this transaction could + * matter. + * + * When the summarize flag is set, we've run short of room for sxact data + * and must summarize to the SLRU. Predicate locks are transferred to a + * dummy "old" transaction, with duplicate locks on a single target + * collapsing to a single lock with the "latest" commitSeqNo from among + * the conflicting locks.. + */ +static void +ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial, + bool summarize) +{ + PREDICATELOCK *predlock; + SERIALIZABLEXIDTAG sxidtag; + RWConflict conflict, + nextConflict; + + Assert(sxact != NULL); + Assert(SxactIsRolledBack(sxact) || SxactIsCommitted(sxact)); + Assert(LWLockHeldByMe(SerializableFinishedListLock)); + + LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); + predlock = (PREDICATELOCK *) + SHMQueueNext(&(sxact->predicateLocks), + &(sxact->predicateLocks), + offsetof(PREDICATELOCK, xactLink)); + while (predlock) + { + PREDICATELOCK *nextpredlock; + PREDICATELOCKTAG tag; + SHM_QUEUE *targetLink; + PREDICATELOCKTARGET *target; + PREDICATELOCKTARGETTAG targettag; + uint32 targettaghash; + LWLockId partitionLock; + + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&(sxact->predicateLocks), + &(predlock->xactLink), + offsetof(PREDICATELOCK, xactLink)); + + tag = predlock->tag; + targetLink = &(predlock->targetLink); + target = tag.myTarget; + targettag = target->tag; + targettaghash = PredicateLockTargetTagHashCode(&targettag); + partitionLock = PredicateLockHashPartitionLock(targettaghash); + + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + + SHMQueueDelete(targetLink); + + hash_search_with_hash_value(PredicateLockHash, &tag, + PredicateLockHashCodeFromTargetHashCode(&tag, + targettaghash), + HASH_REMOVE, NULL); + if (summarize) + { + bool found; + + /* Fold into dummy transaction list. */ + tag.myXact = OldCommittedSxact; + predlock = hash_search_with_hash_value(PredicateLockHash, &tag, + PredicateLockHashCodeFromTargetHashCode(&tag, + targettaghash), + HASH_ENTER, &found); + if (!predlock) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"), + errhint("You might need to increase max_predicate_locks_per_transaction."))); + if (found) + { + if (predlock->commitSeqNo < sxact->commitSeqNo) + predlock->commitSeqNo = sxact->commitSeqNo; + } + else + { + SHMQueueInsertBefore(&(target->predicateLocks), + &(predlock->targetLink)); + SHMQueueInsertBefore(&(OldCommittedSxact->predicateLocks), + &(predlock->xactLink)); + predlock->commitSeqNo = sxact->commitSeqNo; + } + } + else + RemoveTargetIfNoLongerUsed(target, targettaghash); + + LWLockRelease(partitionLock); + + predlock = nextpredlock; + } + + /* + * Rather than retail removal, just re-init the head after we've run + * through the list. + */ + SHMQueueInit(&sxact->predicateLocks); + + LWLockRelease(SerializablePredicateLockListLock); + + sxidtag.xid = sxact->topXid; + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + + if (!partial) + { + /* Release all outConflicts. */ + conflict = (RWConflict) + SHMQueueNext(&sxact->outConflicts, + &sxact->outConflicts, + offsetof(RWConflictData, outLink)); + while (conflict) + { + nextConflict = (RWConflict) + SHMQueueNext(&sxact->outConflicts, + &conflict->outLink, + offsetof(RWConflictData, outLink)); + if (summarize) + conflict->sxactIn->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN; + ReleaseRWConflict(conflict); + conflict = nextConflict; + } + } + + /* Release all inConflicts. */ + conflict = (RWConflict) + SHMQueueNext(&sxact->inConflicts, + &sxact->inConflicts, + offsetof(RWConflictData, inLink)); + while (conflict) + { + nextConflict = (RWConflict) + SHMQueueNext(&sxact->inConflicts, + &conflict->inLink, + offsetof(RWConflictData, inLink)); + if (summarize) + conflict->sxactOut->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; + ReleaseRWConflict(conflict); + conflict = nextConflict; + } + + if (!partial) + { + /* Get rid of the xid and the record of the transaction itself. */ + if (sxidtag.xid != InvalidTransactionId) + hash_search(SerializableXidHash, &sxidtag, HASH_REMOVE, NULL); + ReleasePredXact(sxact); + } + + LWLockRelease(SerializableXactHashLock); +} + +/* + * Tests whether the given top level transaction is concurrent with + * (overlaps) our current transaction. + * + * We need to identify the top level transaction for SSI, anyway, so pass + * that to this function to save the overhead of checking the snapshot's + * subxip array. + */ +static bool +XidIsConcurrent(TransactionId xid) +{ + Snapshot snap; + uint32 i; + + Assert(TransactionIdIsValid(xid)); + Assert(!TransactionIdEquals(xid, GetTopTransactionIdIfAny())); + + snap = GetTransactionSnapshot(); + + if (TransactionIdPrecedes(xid, snap->xmin)) + return false; + + if (TransactionIdFollowsOrEquals(xid, snap->xmax)) + return true; + + for (i = 0; i < snap->xcnt; i++) + { + if (xid == snap->xip[i]) + return true; + } + + return false; +} + +/* + * CheckForSerializableConflictOut + * We are reading a tuple which has been modified. If it is visible to + * us but has been deleted, that indicates a rw-conflict out. If it's + * not visible and was created by a concurrent (overlapping) + * serializable transaction, that is also a rw-conflict out, + * + * We will determine the top level xid of the writing transaction with which + * we may be in conflict, and check for overlap with our own transaction. + * If the transactions overlap (i.e., they cannot see each other's writes), + * then we have a conflict out. + * + * This function should be called just about anywhere in heapam.c that a + * tuple has been read. There is currently no known reason to call this + * function from an index AM. + */ +void +CheckForSerializableConflictOut(const bool visible, const Relation relation, + const HeapTuple tuple, const Buffer buffer) +{ + TransactionId xid; + SERIALIZABLEXIDTAG sxidtag; + SERIALIZABLEXID *sxid; + SERIALIZABLEXACT *sxact; + HTSV_Result htsvResult; + + if (SkipSerialization(relation)) + return; + + if (SxactIsMarkedForDeath(MySerializableXact)) + { + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on identification as a pivot, during conflict out checking."), + errhint("The transaction might succeed if retried."))); + } + + /* + * Check to see whether the tuple has been written to by a concurrent + * transaction, either to create it not visible to us, or to delete it + * while it is visible to us. The "visible" bool indicates whether the + * tuple is visible to us, while HeapTupleSatisfiesVacuum checks what else + * is going on with it. + */ + htsvResult = HeapTupleSatisfiesVacuum(tuple->t_data, TransactionXmin, buffer); + switch (htsvResult) + { + case HEAPTUPLE_LIVE: + if (visible) + return; + xid = HeapTupleHeaderGetXmin(tuple->t_data); + break; + case HEAPTUPLE_RECENTLY_DEAD: + if (!visible) + return; + xid = HeapTupleHeaderGetXmax(tuple->t_data); + break; + case HEAPTUPLE_DELETE_IN_PROGRESS: + xid = HeapTupleHeaderGetXmax(tuple->t_data); + break; + case HEAPTUPLE_INSERT_IN_PROGRESS: + xid = HeapTupleHeaderGetXmin(tuple->t_data); + break; + case HEAPTUPLE_DEAD: + return; + default: + + /* + * The only way to get to this default clause is if a new value is + * added to the enum type without adding it to this switch + * statement. That's a bug, so elog. + */ + elog(ERROR, "unrecognized return value from HeapTupleSatisfiesVacuum: %u", htsvResult); + + /* + * In spite of having all enum values covered and calling elog on + * this default, some compilers think this is a code path which + * allows xid to be used below without initialization. Silence + * that warning. + */ + xid = InvalidTransactionId; + } + Assert(TransactionIdIsValid(xid)); + Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin)); + + /* + * Find top level xid. Bail out if xid is too early to be a conflict, or + * if it's our own xid. + */ + if (TransactionIdEquals(xid, GetTopTransactionIdIfAny())) + return; + xid = SubTransGetTopmostTransaction(xid); + if (TransactionIdPrecedes(xid, TransactionXmin)) + return; + if (TransactionIdEquals(xid, GetTopTransactionIdIfAny())) + return; + + /* + * Find sxact or summarized info for the top level xid. + */ + sxidtag.xid = xid; + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + sxid = (SERIALIZABLEXID *) + hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL); + if (!sxid) + { + /* + * Transaction not found in "normal" SSI structures. Check whether it + * got pushed out to SLRU storage for "old committed" transactions. + */ + SerCommitSeqNo conflictCommitSeqNo; + + conflictCommitSeqNo = OldSerXidGetMinConflictCommitSeqNo(xid); + if (conflictCommitSeqNo != 0) + { + if (conflictCommitSeqNo != InvalidSerCommitSeqNo + && (!SxactIsReadOnly(MySerializableXact) + || conflictCommitSeqNo + <= MySerializableXact->SeqNo.lastCommitBeforeSnapshot)) + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on conflict out to old pivot %u.", xid), + errhint("The transaction might succeed if retried."))); + + if (SxactHasSummaryConflictIn(MySerializableXact) + || !SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->inConflicts)) + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on identification as a pivot, with conflict out to old committed transaction %u.", xid), + errhint("The transaction might succeed if retried."))); + + MySerializableXact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; + } + + /* It's not serializable or otherwise not important. */ + LWLockRelease(SerializableXactHashLock); + return; + } + sxact = sxid->myXact; + Assert(TransactionIdEquals(sxact->topXid, xid)); + if (sxact == MySerializableXact + || SxactIsRolledBack(sxact) + || SxactIsMarkedForDeath(sxact)) + { + /* We can't conflict with our own transaction or one rolled back. */ + LWLockRelease(SerializableXactHashLock); + return; + } + + /* + * We have a conflict out to a transaction which has a conflict out to a + * summarized transaction. That summarized transaction must have + * committed first, and we can't tell when it committed in relation to our + * snapshot acquisition, so something needs to be cancelled. + */ + if (SxactHasSummaryConflictOut(sxact)) + { + if (!SxactIsPrepared(sxact)) + { + sxact->flags |= SXACT_FLAG_MARKED_FOR_DEATH; + LWLockRelease(SerializableXactHashLock); + return; + } + else + { + LWLockRelease(SerializableXactHashLock); + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on conflict out to old pivot."), + errhint("The transaction might succeed if retried."))); + } + } + + /* + * If this is a read-only transaction and the writing transaction has + * committed, and it doesn't have a rw-conflict to a transaction which + * committed before it, no conflict. + */ + if (SxactIsReadOnly(MySerializableXact) + && SxactIsCommitted(sxact) + && !SxactHasSummaryConflictOut(sxact) + && (!SxactHasConflictOut(sxact) + || MySerializableXact->SeqNo.lastCommitBeforeSnapshot < sxact->SeqNo.earliestOutConflictCommit)) + { + /* Read-only transaction will appear to run first. No conflict. */ + LWLockRelease(SerializableXactHashLock); + return; + } + + if (!XidIsConcurrent(xid)) + { + /* This write was already in our snapshot; no conflict. */ + LWLockRelease(SerializableXactHashLock); + return; + } + + if (RWConflictExists((SERIALIZABLEXACT *) MySerializableXact, sxact)) + { + /* We don't want duplicate conflict records in the list. */ + LWLockRelease(SerializableXactHashLock); + return; + } + + /* + * Flag the conflict. But first, if this conflict creates a dangerous + * structure, ereport an error. + */ + FlagRWConflict((SERIALIZABLEXACT *) MySerializableXact, sxact); + LWLockRelease(SerializableXactHashLock); +} + +/* + * Check a particular target for rw-dependency conflict in. This will + * also check prior versions of a tuple, if any. + */ +static void +CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag) +{ + PREDICATELOCKTARGETTAG nexttargettag; + PREDICATELOCKTARGETTAG thistargettag; + + for (;;) + { + if (!CheckSingleTargetForConflictsIn(targettag, &nexttargettag)) + break; + thistargettag = nexttargettag; + targettag = &thistargettag; + } +} + +/* + * Check a particular target for rw-dependency conflict in. If the tuple + * has prior versions, returns true and *nexttargettag is set to the tag + * of the prior tuple version. + */ +static bool +CheckSingleTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag, + PREDICATELOCKTARGETTAG *nexttargettag) +{ + uint32 targettaghash; + LWLockId partitionLock; + PREDICATELOCKTARGET *target; + PREDICATELOCK *predlock; + bool hasnexttarget = false; + + Assert(MySerializableXact != InvalidSerializableXact); + + /* + * The same hash and LW lock apply to the lock target and the lock itself. + */ + targettaghash = PredicateLockTargetTagHashCode(targettag); + partitionLock = PredicateLockHashPartitionLock(targettaghash); + LWLockAcquire(partitionLock, LW_SHARED); + LWLockAcquire(PredicateLockNextRowLinkLock, LW_SHARED); + target = (PREDICATELOCKTARGET *) + hash_search_with_hash_value(PredicateLockTargetHash, + targettag, targettaghash, + HASH_FIND, NULL); + if (!target) + { + /* Nothing has this target locked; we're done here. */ + LWLockRelease(PredicateLockNextRowLinkLock); + LWLockRelease(partitionLock); + return false; + } + + /* + * If the target is linked to a prior version of the row, save the tag so + * that it can be used for iterative calls to this function. + */ + if (target->priorVersionOfRow != NULL) + { + *nexttargettag = target->priorVersionOfRow->tag; + hasnexttarget = true; + } + LWLockRelease(PredicateLockNextRowLinkLock); + + /* + * Each lock for an overlapping transaction represents a conflict: a + * rw-dependency in to this transaction. + */ + predlock = (PREDICATELOCK *) + SHMQueueNext(&(target->predicateLocks), + &(target->predicateLocks), + offsetof(PREDICATELOCK, targetLink)); + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + while (predlock) + { + SHM_QUEUE *predlocktargetlink; + PREDICATELOCK *nextpredlock; + SERIALIZABLEXACT *sxact; + + predlocktargetlink = &(predlock->targetLink); + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&(target->predicateLocks), + predlocktargetlink, + offsetof(PREDICATELOCK, targetLink)); + + sxact = predlock->tag.myXact; + if (sxact == MySerializableXact) + { + /* + * If we're getting a write lock on the tuple, we don't need a + * predicate (SIREAD) lock. At this point our transaction already + * has an ExclusiveRowLock on the relation, so we are OK to drop + * the predicate lock on the tuple, if found, without fearing that + * another write against the tuple will occur before the MVCC + * information makes it to the buffer. + */ + if (GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag)) + { + uint32 predlockhashcode; + PREDICATELOCKTARGET *rmtarget = NULL; + PREDICATELOCK *rmpredlock; + LOCALPREDICATELOCK *locallock, + *rmlocallock; + + /* + * This is a tuple on which we have a tuple predicate lock. We + * only have shared LW locks now; release those, and get + * exclusive locks only while we modify things. + */ + LWLockRelease(SerializableXactHashLock); + LWLockRelease(partitionLock); + LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + + /* + * Remove the predicate lock from shared memory, if it wasn't + * removed while the locks were released. One way that could + * happen is from autovacuum cleaning up an index. + */ + predlockhashcode = PredicateLockHashCodeFromTargetHashCode + (&(predlock->tag), targettaghash); + rmpredlock = (PREDICATELOCK *) + hash_search_with_hash_value(PredicateLockHash, + &(predlock->tag), + predlockhashcode, + HASH_FIND, NULL); + if (rmpredlock) + { + Assert(rmpredlock == predlock); + + SHMQueueDelete(predlocktargetlink); + SHMQueueDelete(&(predlock->xactLink)); + + rmpredlock = (PREDICATELOCK *) + hash_search_with_hash_value(PredicateLockHash, + &(predlock->tag), + predlockhashcode, + HASH_REMOVE, NULL); + Assert(rmpredlock == predlock); + + RemoveTargetIfNoLongerUsed(target, targettaghash); + + LWLockRelease(SerializableXactHashLock); + LWLockRelease(partitionLock); + LWLockRelease(SerializablePredicateLockListLock); + + locallock = (LOCALPREDICATELOCK *) + hash_search_with_hash_value(LocalPredicateLockHash, + targettag, targettaghash, + HASH_FIND, NULL); + Assert(locallock != NULL); + Assert(locallock->held); + locallock->held = false; + + if (locallock->childLocks == 0) + { + rmlocallock = (LOCALPREDICATELOCK *) + hash_search_with_hash_value(LocalPredicateLockHash, + targettag, targettaghash, + HASH_REMOVE, NULL); + Assert(rmlocallock == locallock); + } + + DecrementParentLocks(targettag); + + /* + * If we've cleaned up the last of the predicate locks for + * the target, bail out before re-acquiring the locks. + */ + if (rmtarget) + return hasnexttarget; + + /* + * The list has been altered. Start over at the front. + */ + LWLockAcquire(partitionLock, LW_SHARED); + nextpredlock = (PREDICATELOCK *) + SHMQueueNext(&(target->predicateLocks), + &(target->predicateLocks), + offsetof(PREDICATELOCK, targetLink)); + + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + } + else + { + /* + * The predicate lock was cleared while we were attempting + * to upgrade our lightweight locks. Revert to the shared + * locks. + */ + LWLockRelease(SerializableXactHashLock); + LWLockRelease(partitionLock); + LWLockRelease(SerializablePredicateLockListLock); + LWLockAcquire(partitionLock, LW_SHARED); + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + } + } + } + else if (!SxactIsRolledBack(sxact) + && (!SxactIsCommitted(sxact) + || TransactionIdPrecedes(GetTransactionSnapshot()->xmin, + sxact->finishedBefore)) + && !RWConflictExists(sxact, (SERIALIZABLEXACT *) MySerializableXact)) + { + LWLockRelease(SerializableXactHashLock); + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + + FlagRWConflict(sxact, (SERIALIZABLEXACT *) MySerializableXact); + + LWLockRelease(SerializableXactHashLock); + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + } + + predlock = nextpredlock; + } + LWLockRelease(SerializableXactHashLock); + LWLockRelease(partitionLock); + + return hasnexttarget; +} + +/* + * CheckForSerializableConflictIn + * We are writing the given tuple. If that indicates a rw-conflict + * in from another serializable transaction, take appropriate action. + * + * Skip checking for any granularity for which a parameter is missing. + * + * A tuple update or delete is in conflict if we have a predicate lock + * against the relation or page in which the tuple exists, or against the + * tuple itself. + */ +void +CheckForSerializableConflictIn(const Relation relation, const HeapTuple tuple, + const Buffer buffer) +{ + PREDICATELOCKTARGETTAG targettag; + + if (SkipSerialization(relation)) + return; + + if (SxactIsMarkedForDeath(MySerializableXact)) + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on identification as a pivot, during conflict in checking."), + errhint("The transaction might succeed if retried."))); + + MySerializableXact->flags |= SXACT_FLAG_DID_WRITE; + + /* + * It is important that we check for locks from the finest granularity to + * the coarsest granularity, so that granularity promotion doesn't cause + * us to miss a lock. The new (coarser) lock will be acquired before the + * old (finer) locks are released. + * + * It is not possible to take and hold a lock across the checks for all + * granularities because each target could be in a separate partition. + */ + if (tuple != NULL) + { + SET_PREDICATELOCKTARGETTAG_TUPLE(targettag, + relation->rd_node.dbNode, + relation->rd_id, + ItemPointerGetBlockNumber(&(tuple->t_data->t_ctid)), + ItemPointerGetOffsetNumber(&(tuple->t_data->t_ctid))); + CheckTargetForConflictsIn(&targettag); + } + + if (BufferIsValid(buffer)) + { + SET_PREDICATELOCKTARGETTAG_PAGE(targettag, + relation->rd_node.dbNode, + relation->rd_id, + BufferGetBlockNumber(buffer)); + CheckTargetForConflictsIn(&targettag); + } + + SET_PREDICATELOCKTARGETTAG_RELATION(targettag, + relation->rd_node.dbNode, + relation->rd_id); + CheckTargetForConflictsIn(&targettag); +} + +/* + * Flag a rw-dependency between two serializable transactions. + * + * The caller is responsible for ensuring that we have a LW lock on + * the transaction hash table. + */ +static void +FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer) +{ + Assert(reader != writer); + + /* First, see if this conflict causes failure. */ + OnConflict_CheckForSerializationFailure(reader, writer); + + /* Actually do the conflict flagging. */ + if (reader == OldCommittedSxact) + writer->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN; + else if (writer == OldCommittedSxact) + reader->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; + else + SetRWConflict(reader, writer); +} + +/* + * Check whether we should roll back one of these transactions + * instead of flagging a new rw-conflict. + */ +static void +OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader, + SERIALIZABLEXACT *writer) +{ + bool failure; + RWConflict conflict; + + Assert(LWLockHeldByMe(SerializableXactHashLock)); + + failure = false; + + /* + * Check for already-committed writer with rw-conflict out flagged. This + * means that the reader must immediately fail. + */ + if (SxactIsCommitted(writer) + && (SxactHasConflictOut(writer) || SxactHasSummaryConflictOut(writer))) + failure = true; + + /* + * Check whether the reader has become a pivot with a committed writer. If + * so, we must roll back unless every in-conflict either committed before + * the writer committed or is READ ONLY and overlaps the writer. + */ + if (!failure && SxactIsCommitted(writer) && !SxactIsReadOnly(reader)) + { + if (SxactHasSummaryConflictIn(reader)) + { + failure = true; + conflict = NULL; + } + else + conflict = (RWConflict) + SHMQueueNext(&reader->inConflicts, + &reader->inConflicts, + offsetof(RWConflictData, inLink)); + while (conflict) + { + if (!SxactIsRolledBack(conflict->sxactOut) + && (!SxactIsCommitted(conflict->sxactOut) + || conflict->sxactOut->commitSeqNo >= writer->commitSeqNo) + && (!SxactIsReadOnly(conflict->sxactOut) + || conflict->sxactOut->SeqNo.lastCommitBeforeSnapshot >= writer->commitSeqNo)) + { + failure = true; + break; + } + conflict = (RWConflict) + SHMQueueNext(&reader->inConflicts, + &conflict->inLink, + offsetof(RWConflictData, inLink)); + } + } + + /* + * Check whether the writer has become a pivot with an out-conflict + * committed transaction, while neither reader nor writer is committed. If + * the reader is a READ ONLY transaction, there is only a serialization + * failure if an out-conflict transaction causing the pivot committed + * before the reader acquired its snapshot. (That is, the reader must not + * have been concurrent with the out-conflict transaction.) + */ + if (!failure && !SxactIsCommitted(writer)) + { + if (SxactHasSummaryConflictOut(reader)) + { + failure = true; + conflict = NULL; + } + else + conflict = (RWConflict) + SHMQueueNext(&writer->outConflicts, + &writer->outConflicts, + offsetof(RWConflictData, outLink)); + while (conflict) + { + if ((reader == conflict->sxactIn && SxactIsCommitted(reader)) + || (SxactIsCommitted(conflict->sxactIn) + && !SxactIsCommitted(reader) + && (!SxactIsReadOnly(reader) + || conflict->sxactIn->commitSeqNo <= reader->SeqNo.lastCommitBeforeSnapshot))) + { + failure = true; + break; + } + conflict = (RWConflict) + SHMQueueNext(&writer->outConflicts, + &conflict->outLink, + offsetof(RWConflictData, outLink)); + } + } + + if (failure) + { + if (MySerializableXact == writer) + { + LWLockRelease(SerializableXactHashLock); + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on identification as pivot, during write."), + errhint("The transaction might succeed if retried."))); + } + else if (SxactIsPrepared(writer)) + { + LWLockRelease(SerializableXactHashLock); + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on conflict out to pivot %u, during read.", writer->topXid), + errhint("The transaction might succeed if retried."))); + } + writer->flags |= SXACT_FLAG_MARKED_FOR_DEATH; + } +} + +/* + * PreCommit_CheckForSerializableConflicts + * Check for dangerous structures in a serializable transaction + * at commit. + * + * We're checking for a dangerous structure as each conflict is recorded. + * The only way we could have a problem at commit is if this is the "out" + * side of a pivot, and neither the "in" side nor the pivot has yet + * committed. + * + * If a dangerous structure is found, the pivot (the near conflict) is + * marked for death, because rolling back another transaction might mean + * that we flail without ever making progress. This transaction is + * committing writes, so letting it commit ensures progress. If we + * cancelled the far conflict, it might immediately fail again on retry. + */ +void +PreCommit_CheckForSerializationFailure(void) +{ + RWConflict nearConflict; + + if (MySerializableXact == InvalidSerializableXact) + return; + + Assert(IsolationIsSerializable()); + + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + + if (SxactIsMarkedForDeath(MySerializableXact)) + { + LWLockRelease(SerializableXactHashLock); + ereport(ERROR, + (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), + errmsg("could not serialize access due to read/write dependencies among transactions"), + errdetail("Cancelled on identification as a pivot, during commit attempt."), + errhint("The transaction might succeed if retried."))); + } + + nearConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, + (SHM_QUEUE *) &MySerializableXact->inConflicts, + offsetof(RWConflictData, inLink)); + while (nearConflict) + { + if (!SxactIsCommitted(nearConflict->sxactOut) + && !SxactIsRolledBack(nearConflict->sxactOut) + && !SxactIsMarkedForDeath(nearConflict->sxactOut)) + { + RWConflict farConflict; + + farConflict = (RWConflict) + SHMQueueNext(&nearConflict->sxactOut->inConflicts, + &nearConflict->sxactOut->inConflicts, + offsetof(RWConflictData, inLink)); + while (farConflict) + { + if (farConflict->sxactOut == MySerializableXact + || (!SxactIsCommitted(farConflict->sxactOut) + && !SxactIsReadOnly(farConflict->sxactOut) + && !SxactIsRolledBack(farConflict->sxactOut) + && !SxactIsMarkedForDeath(farConflict->sxactOut))) + { + nearConflict->sxactOut->flags |= SXACT_FLAG_MARKED_FOR_DEATH; + break; + } + farConflict = (RWConflict) + SHMQueueNext(&nearConflict->sxactOut->inConflicts, + &farConflict->inLink, + offsetof(RWConflictData, inLink)); + } + } + + nearConflict = (RWConflict) + SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, + &nearConflict->inLink, + offsetof(RWConflictData, inLink)); + } + + MySerializableXact->flags |= SXACT_FLAG_PREPARED; + + LWLockRelease(SerializableXactHashLock); +} + +/*------------------------------------------------------------------------*/ + +/* + * Two-phase commit support + */ + +/* + * AtPrepare_Locks + * Do the preparatory work for a PREPARE: make 2PC state file + * records for all predicate locks currently held. + */ +void +AtPrepare_PredicateLocks(void) +{ + PREDICATELOCK *predlock; + SERIALIZABLEXACT *sxact; + TwoPhasePredicateRecord record; + TwoPhasePredicateXactRecord *xactRecord; + TwoPhasePredicateLockRecord *lockRecord; + + sxact = (SERIALIZABLEXACT *) MySerializableXact; + xactRecord = &(record.data.xactRecord); + lockRecord = &(record.data.lockRecord); + + if (MySerializableXact == InvalidSerializableXact) + return; + + /* Generate a xact record for our SERIALIZABLEXACT */ + record.type = TWOPHASEPREDICATERECORD_XACT; + xactRecord->xmin = MySerializableXact->xmin; + xactRecord->flags = MySerializableXact->flags; + + /* + * Tweak the flags. Since we're not going to output the inConflicts and + * outConflicts lists, if they're non-empty we'll represent that by + * setting the appropriate summary conflict flags. + */ + if (!SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->inConflicts)) + xactRecord->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN; + if (!SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->outConflicts)) + xactRecord->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; + + RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0, + &record, sizeof(record)); + + /* + * Generate a lock record for each lock. + * + * To do this, we need to walk the predicate lock list in our sxact rather + * than using the local predicate lock table because the latter is not + * guaranteed to be accurate. + */ + LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); + + predlock = (PREDICATELOCK *) + SHMQueueNext(&(sxact->predicateLocks), + &(sxact->predicateLocks), + offsetof(PREDICATELOCK, xactLink)); + + while (predlock != NULL) + { + record.type = TWOPHASEPREDICATERECORD_LOCK; + lockRecord->target = predlock->tag.myTarget->tag; + + RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0, + &record, sizeof(record)); + + predlock = (PREDICATELOCK *) + SHMQueueNext(&(sxact->predicateLocks), + &(predlock->xactLink), + offsetof(PREDICATELOCK, xactLink)); + } + + LWLockRelease(SerializablePredicateLockListLock); +} + +/* + * PostPrepare_Locks + * Clean up after successful PREPARE. Unlike the non-predicate + * lock manager, we do not need to transfer locks to a dummy + * PGPROC because our SERIALIZABLEXACT will stay around + * anyway. We only need to clean up our local state. + */ +void +PostPrepare_PredicateLocks(TransactionId xid) +{ + if (MySerializableXact == InvalidSerializableXact) + return; + + Assert(SxactIsPrepared(MySerializableXact)); + + MySerializableXact->pid = 0; + + hash_destroy(LocalPredicateLockHash); + LocalPredicateLockHash = NULL; + + MySerializableXact = InvalidSerializableXact; +} + +/* + * PredicateLockTwoPhaseFinish + * Release a prepared transaction's predicate locks once it + * commits or aborts. + */ +void +PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit) +{ + SERIALIZABLEXID *sxid; + SERIALIZABLEXIDTAG sxidtag; + + sxidtag.xid = xid; + + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + sxid = (SERIALIZABLEXID *) + hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL); + LWLockRelease(SerializableXactHashLock); + + /* xid will not be found if it wasn't a serializable transaction */ + if (sxid == NULL) + return; + + /* Release its locks */ + MySerializableXact = sxid->myXact; + ReleasePredicateLocks(isCommit); +} + +/* + * Re-acquire a predicate lock belonging to a transaction that was prepared. + */ +void +predicatelock_twophase_recover(TransactionId xid, uint16 info, + void *recdata, uint32 len) +{ + TwoPhasePredicateRecord *record; + + Assert(len == sizeof(TwoPhasePredicateRecord)); + + record = (TwoPhasePredicateRecord *) recdata; + + Assert((record->type == TWOPHASEPREDICATERECORD_XACT) || + (record->type == TWOPHASEPREDICATERECORD_LOCK)); + + if (record->type == TWOPHASEPREDICATERECORD_XACT) + { + /* Per-transaction record. Set up a SERIALIZABLEXACT. */ + TwoPhasePredicateXactRecord *xactRecord; + SERIALIZABLEXACT *sxact; + SERIALIZABLEXID *sxid; + SERIALIZABLEXIDTAG sxidtag; + bool found; + + xactRecord = (TwoPhasePredicateXactRecord *) &record->data.xactRecord; + + LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); + sxact = CreatePredXact(); + if (!sxact) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"))); + + /* vxid for a prepared xact is InvalidBackendId/xid; no pid */ + sxact->vxid.backendId = InvalidBackendId; + sxact->vxid.localTransactionId = (LocalTransactionId) xid; + sxact->pid = 0; + + /* a prepared xact hasn't committed yet */ + sxact->commitSeqNo = InvalidSerCommitSeqNo; + sxact->finishedBefore = InvalidTransactionId; + + sxact->SeqNo.lastCommitBeforeSnapshot = RecoverySerCommitSeqNo; + + + /* + * We don't need the details of a prepared transaction's conflicts, + * just whether it had conflicts in or out (which we get from the + * flags) + */ + SHMQueueInit(&(sxact->outConflicts)); + SHMQueueInit(&(sxact->inConflicts)); + + /* + * Don't need to track this; no transactions running at the time the + * recovered xact started are still active, except possibly other + * prepared xacts and we don't care whether those are RO_SAFE or not. + */ + SHMQueueInit(&(sxact->possibleUnsafeConflicts)); + + SHMQueueInit(&(sxact->predicateLocks)); + SHMQueueElemInit(&(sxact->finishedLink)); + + sxact->topXid = xid; + sxact->xmin = xactRecord->xmin; + sxact->flags = xactRecord->flags; + Assert(SxactIsPrepared(sxact)); + if (!SxactIsReadOnly(sxact)) + { + ++(PredXact->WritableSxactCount); + Assert(PredXact->WritableSxactCount <= + (MaxBackends + max_prepared_xacts)); + } + + /* Register the transaction's xid */ + sxidtag.xid = xid; + sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, + &sxidtag, + HASH_ENTER, &found); + if (!sxid) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of shared memory"))); + Assert(!found); + sxid->myXact = (SERIALIZABLEXACT *) sxact; + + /* + * Update global xmin. Note that this is a special case compared to + * registering a normal transaction, because the global xmin might go + * backwards. That's OK, because until recovery is over we're not + * going to complete any transactions or create any non-prepared + * transactions, so there's no danger of throwing away. + */ + if ((!TransactionIdIsValid(PredXact->SxactGlobalXmin)) || + (TransactionIdFollows(PredXact->SxactGlobalXmin, sxact->xmin))) + { + PredXact->SxactGlobalXmin = sxact->xmin; + PredXact->SxactGlobalXminCount = 1; + OldSerXidSetActiveSerXmin(sxact->xmin); + } + else if (TransactionIdEquals(sxact->xmin, PredXact->SxactGlobalXmin)) + { + Assert(PredXact->SxactGlobalXminCount > 0); + PredXact->SxactGlobalXminCount++; + } + + LWLockRelease(SerializableXactHashLock); + } + else if (record->type == TWOPHASEPREDICATERECORD_LOCK) + { + /* Lock record. Recreate the PREDICATELOCK */ + TwoPhasePredicateLockRecord *lockRecord; + SERIALIZABLEXID *sxid; + SERIALIZABLEXACT *sxact; + SERIALIZABLEXIDTAG sxidtag; + uint32 targettaghash; + + lockRecord = (TwoPhasePredicateLockRecord *) &record->data.lockRecord; + targettaghash = PredicateLockTargetTagHashCode(&lockRecord->target); + + LWLockAcquire(SerializableXactHashLock, LW_SHARED); + sxidtag.xid = xid; + sxid = (SERIALIZABLEXID *) + hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL); + LWLockRelease(SerializableXactHashLock); + + Assert(sxid != NULL); + sxact = sxid->myXact; + Assert(sxact != InvalidSerializableXact); + + CreatePredicateLock(&lockRecord->target, targettaghash, sxact); + } +} |