diff options
Diffstat (limited to 'src/backend/access/transam/varsup.c')
| -rw-r--r-- | src/backend/access/transam/varsup.c | 27 |
1 files changed, 20 insertions, 7 deletions
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c index f245a79cedb..2b253fc5855 100644 --- a/src/backend/access/transam/varsup.c +++ b/src/backend/access/transam/varsup.c @@ -6,7 +6,7 @@ * Copyright (c) 2000, PostgreSQL Global Development Group * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.40 2001/05/25 15:45:32 momjian Exp $ + * $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.41 2001/07/12 04:11:13 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -18,8 +18,7 @@ #include "storage/proc.h" -/* Number of XIDs and OIDs to prefetch (preallocate) per XLOG write */ -#define VAR_XID_PREFETCH 1024 +/* Number of OIDs to prefetch (preallocate) per XLOG write */ #define VAR_OID_PREFETCH 8192 /* Spinlocks for serializing generation of XIDs and OIDs, respectively */ @@ -29,10 +28,13 @@ SPINLOCK OidGenLockId; /* pointer to "variable cache" in shared memory (set up by shmem.c) */ VariableCache ShmemVariableCache = NULL; + +/* + * Allocate the next XID for my new transaction. + */ void GetNewTransactionId(TransactionId *xid) { - /* * During bootstrap initialization, we return the special bootstrap * transaction id. @@ -49,10 +51,22 @@ GetNewTransactionId(TransactionId *xid) (ShmemVariableCache->nextXid)++; - SpinRelease(XidGenLockId); - + /* + * Must set MyProc->xid before releasing XidGenLock. This ensures that + * when GetSnapshotData calls ReadNewTransactionId, all active XIDs + * before the returned value of nextXid are already present in the shared + * PROC array. Else we have a race condition. + * + * XXX by storing xid into MyProc without acquiring SInvalLock, we are + * relying on fetch/store of an xid to be atomic, else other backends + * might see a partially-set xid here. But holding both locks at once + * would be a nasty concurrency hit (and at this writing, could cause a + * deadlock against GetSnapshotData). So for now, assume atomicity. + */ if (MyProc != (PROC *) NULL) MyProc->xid = *xid; + + SpinRelease(XidGenLockId); } /* @@ -61,7 +75,6 @@ GetNewTransactionId(TransactionId *xid) void ReadNewTransactionId(TransactionId *xid) { - /* * During bootstrap initialization, we return the special bootstrap * transaction id. |