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Repair incorrect order of operations in GetNewTransactionId(). We must

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complete ExtendCLOG() before advancing nextXid, so that if that routine
fails, the next incoming transaction will try it again.  Per trouble
report from Christopher Kings-Lynne.
This commit is contained in:
Tom Lane 2004-01-26 19:16:23 +00:00
parent ac760b6bff
commit a51d4b8dc0
1 changed files with 11 additions and 5 deletions
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16
src/backend/access/transam/varsup.c
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@ -6,7 +6,7 @@
* Copyright (c) 2000-2003, PostgreSQL Global Development Group
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.52 2003/08/04 23:59:37 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.52.4.1 2004/01/26 19:16:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -45,10 +45,8 @@ GetNewTransactionId(void)
xid = ShmemVariableCache->nextXid;
TransactionIdAdvance(ShmemVariableCache->nextXid);
/*
* If we have just allocated the first XID of a new page of the commit
* 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
@ -57,6 +55,14 @@ GetNewTransactionId(void)
*/
ExtendCLOG(xid);
/*
* 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.
*/
TransactionIdAdvance(ShmemVariableCache->nextXid);
/*
* Must set MyProc->xid before releasing XidGenLock. This ensures
* that when GetSnapshotData calls ReadNewTransactionId, all active
@ -74,7 +80,7 @@ GetNewTransactionId(void)
*
* 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.
* (SInvalLock would then mean primarily that PROCs couldn't be added/
* (SInvalLock would then mean primarily that PGPROCs couldn't be added/
* removed while holding the lock.)
*/
if (MyProc != (PGPROC *) NULL)