diff options
Diffstat (limited to 'src/backend/utils/cache/syscache.c')
| -rw-r--r-- | src/backend/utils/cache/syscache.c | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/src/backend/utils/cache/syscache.c b/src/backend/utils/cache/syscache.c index 3e03dfc9910..50c9440f792 100644 --- a/src/backend/utils/cache/syscache.c +++ b/src/backend/utils/cache/syscache.c @@ -30,7 +30,10 @@ #include "catalog/pg_shseclabel_d.h" #include "common/int.h" #include "lib/qunique.h" +#include "miscadmin.h" +#include "storage/lmgr.h" #include "utils/catcache.h" +#include "utils/inval.h" #include "utils/lsyscache.h" #include "utils/rel.h" #include "utils/syscache.h" @@ -269,6 +272,98 @@ ReleaseSysCache(HeapTuple tuple) } /* + * SearchSysCacheLocked1 + * + * Combine SearchSysCache1() with acquiring a LOCKTAG_TUPLE at mode + * InplaceUpdateTupleLock. This is a tool for complying with the + * README.tuplock section "Locking to write inplace-updated tables". After + * the caller's heap_update(), it should UnlockTuple(InplaceUpdateTupleLock) + * and ReleaseSysCache(). + * + * The returned tuple may be the subject of an uncommitted update, so this + * doesn't prevent the "tuple concurrently updated" error. + */ +HeapTuple +SearchSysCacheLocked1(int cacheId, + Datum key1) +{ + ItemPointerData tid; + LOCKTAG tag; + Oid dboid = + SysCache[cacheId]->cc_relisshared ? InvalidOid : MyDatabaseId; + Oid reloid = cacheinfo[cacheId].reloid; + + /*---------- + * Since inplace updates may happen just before our LockTuple(), we must + * return content acquired after LockTuple() of the TID we return. If we + * just fetched twice instead of looping, the following sequence would + * defeat our locking: + * + * GRANT: SearchSysCache1() = TID (1,5) + * GRANT: LockTuple(pg_class, (1,5)) + * [no more inplace update of (1,5) until we release the lock] + * CLUSTER: SearchSysCache1() = TID (1,5) + * CLUSTER: heap_update() = TID (1,8) + * CLUSTER: COMMIT + * GRANT: SearchSysCache1() = TID (1,8) + * GRANT: return (1,8) from SearchSysCacheLocked1() + * VACUUM: SearchSysCache1() = TID (1,8) + * VACUUM: LockTuple(pg_class, (1,8)) # two TIDs now locked for one rel + * VACUUM: inplace update + * GRANT: heap_update() = (1,9) # lose inplace update + * + * In the happy case, this takes two fetches, one to determine the TID to + * lock and another to get the content and confirm the TID didn't change. + * + * This is valid even if the row gets updated to a new TID, the old TID + * becomes LP_UNUSED, and the row gets updated back to its old TID. We'd + * still hold the right LOCKTAG_TUPLE and a copy of the row captured after + * the LOCKTAG_TUPLE. + */ + ItemPointerSetInvalid(&tid); + for (;;) + { + HeapTuple tuple; + LOCKMODE lockmode = InplaceUpdateTupleLock; + + tuple = SearchSysCache1(cacheId, key1); + if (ItemPointerIsValid(&tid)) + { + if (!HeapTupleIsValid(tuple)) + { + LockRelease(&tag, lockmode, false); + return tuple; + } + if (ItemPointerEquals(&tid, &tuple->t_self)) + return tuple; + LockRelease(&tag, lockmode, false); + } + else if (!HeapTupleIsValid(tuple)) + return tuple; + + tid = tuple->t_self; + ReleaseSysCache(tuple); + /* like: LockTuple(rel, &tid, lockmode) */ + SET_LOCKTAG_TUPLE(tag, dboid, reloid, + ItemPointerGetBlockNumber(&tid), + ItemPointerGetOffsetNumber(&tid)); + (void) LockAcquire(&tag, lockmode, false, false); + + /* + * If an inplace update just finished, ensure we process the syscache + * inval. XXX this is insufficient: the inplace updater may not yet + * have reached AtEOXact_Inval(). See test at inplace-inval.spec. + * + * If a heap_update() call just released its LOCKTAG_TUPLE, we'll + * probably find the old tuple and reach "tuple concurrently updated". + * If that heap_update() aborts, our LOCKTAG_TUPLE blocks inplace + * updates while our caller works. + */ + AcceptInvalidationMessages(); + } +} + +/* * SearchSysCacheCopy * * A convenience routine that does SearchSysCache and (if successful) @@ -295,6 +390,28 @@ SearchSysCacheCopy(int cacheId, } /* + * SearchSysCacheLockedCopy1 + * + * Meld SearchSysCacheLockedCopy1 with SearchSysCacheCopy(). After the + * caller's heap_update(), it should UnlockTuple(InplaceUpdateTupleLock) and + * heap_freetuple(). + */ +HeapTuple +SearchSysCacheLockedCopy1(int cacheId, + Datum key1) +{ + HeapTuple tuple, + newtuple; + + tuple = SearchSysCacheLocked1(cacheId, key1); + if (!HeapTupleIsValid(tuple)) + return tuple; + newtuple = heap_copytuple(tuple); + ReleaseSysCache(tuple); + return newtuple; +} + +/* * SearchSysCacheExists * * A convenience routine that just probes to see if a tuple can be found. |