diff options
Diffstat (limited to 'src/backend/access/transam/varsup.c')
| -rw-r--r-- | src/backend/access/transam/varsup.c | 41 |
1 files changed, 20 insertions, 21 deletions
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c index cfd78937428..84926ac415a 100644 --- a/src/backend/access/transam/varsup.c +++ b/src/backend/access/transam/varsup.c @@ -6,7 +6,7 @@ * Copyright (c) 2000-2004, PostgreSQL Global Development Group * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/access/transam/varsup.c,v 1.58 2004/08/29 04:12:23 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/access/transam/varsup.c,v 1.59 2004/08/29 05:06:40 momjian Exp $ * *------------------------------------------------------------------------- */ @@ -47,9 +47,9 @@ GetNewTransactionId(bool isSubXact) xid = ShmemVariableCache->nextXid; /* - * If we are allocating the first XID of a new page of the commit - * log, zero out that commit-log page before returning. We must do - * this while holding XidGenLock, else another xact could acquire and + * If we are allocating the first XID of a new page of the commit log, + * zero out that commit-log page before returning. We must do this + * while holding XidGenLock, else another xact could acquire and * commit a later XID before we zero the page. Fortunately, a page of * the commit log holds 32K or more transactions, so we don't have to * do this very often. @@ -61,17 +61,18 @@ GetNewTransactionId(bool isSubXact) /* * Now advance the nextXid counter. This must not happen until after - * we have successfully completed ExtendCLOG() --- if that routine fails, - * we want the next incoming transaction to try it again. We cannot - * assign more XIDs until there is CLOG space for them. + * we have successfully completed ExtendCLOG() --- if that routine + * fails, we want the next incoming transaction to try it again. We + * cannot assign more XIDs until there is CLOG space for them. */ TransactionIdAdvance(ShmemVariableCache->nextXid); /* - * We must store the new XID into the shared PGPROC array before releasing - * XidGenLock. This ensures that when GetSnapshotData calls + * We must store the new XID into the shared PGPROC array before + * releasing XidGenLock. This ensures that when GetSnapshotData calls * ReadNewTransactionId, all active XIDs before the returned value of - * nextXid are already present in PGPROC. Else we have a race condition. + * nextXid are already present in PGPROC. 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 @@ -86,19 +87,19 @@ GetNewTransactionId(bool isSubXact) * * A solution to the atomic-store problem would be to give each PGPROC * its own spinlock used only for fetching/storing that PGPROC's xid - * and related fields. (SInvalLock would then mean primarily that + * and related fields. (SInvalLock would then mean primarily that * PGPROCs couldn't be added/removed while holding the lock.) * * If there's no room to fit a subtransaction XID into PGPROC, set the * cache-overflowed flag instead. This forces readers to look in - * pg_subtrans to map subtransaction XIDs up to top-level XIDs. - * There is a race-condition window, in that the new XID will not - * appear as running until its parent link has been placed into - * pg_subtrans. However, that will happen before anyone could possibly - * have a reason to inquire about the status of the XID, so it seems - * OK. (Snapshots taken during this window *will* include the parent - * XID, so they will deliver the correct answer later on when someone - * does have a reason to inquire.) + * pg_subtrans to map subtransaction XIDs up to top-level XIDs. There + * is a race-condition window, in that the new XID will not appear as + * running until its parent link has been placed into pg_subtrans. + * However, that will happen before anyone could possibly have a + * reason to inquire about the status of the XID, so it seems OK. + * (Snapshots taken during this window *will* include the parent XID, + * so they will deliver the correct answer later on when someone does + * have a reason to inquire.) */ if (MyProc != NULL) { @@ -112,9 +113,7 @@ GetNewTransactionId(bool isSubXact) MyProc->subxids.nxids++; } else - { MyProc->subxids.overflowed = true; - } } } |