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RecentXmin is too recent to use as the cutoff point for accessing

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pg_subtrans --- what we need is the oldest xmin of any snapshot in use
in the current top transaction.  Introduce a new variable TransactionXmin
to play this role.  Fixes intermittent regression failure reported by
Neil Conway.
This commit is contained in:
Tom Lane
2004-09-16 18:35:23 +00:00
parent 8f9f198603
commit 86fff990b2
5 changed files with 41 additions and 27 deletions
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14
src/backend/access/transam/subtrans.c
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@ -22,7 +22,7 @@
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.5 2004/08/29 05:06:40 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.6 2004/09/16 18:35:20 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -105,7 +105,7 @@ SubTransGetParent(TransactionId xid)
TransactionId parent;
/* Can't ask about stuff that might not be around anymore */
Assert(TransactionIdFollowsOrEquals(xid, RecentXmin));
Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
/* Bootstrap and frozen XIDs have no parent */
if (!TransactionIdIsNormal(xid))
@ -129,12 +129,12 @@ SubTransGetParent(TransactionId xid)
*
* Returns the topmost transaction of the given transaction id.
*
* Because we cannot look back further than RecentXmin, it is possible
* Because we cannot look back further than TransactionXmin, it is possible
* that this function will lie and return an intermediate subtransaction ID
* instead of the true topmost parent ID. This is OK, because in practice
* we only care about detecting whether the topmost parent is still running
* or is part of a current snapshot's list of still-running transactions.
* Therefore, any XID before RecentXmin is as good as any other.
* Therefore, any XID before TransactionXmin is as good as any other.
*/
TransactionId
SubTransGetTopmostTransaction(TransactionId xid)
@ -143,12 +143,12 @@ SubTransGetTopmostTransaction(TransactionId xid)
previousXid = xid;
/* Can't ask about stuff that might not be around anymore */
Assert(TransactionIdFollowsOrEquals(xid, RecentXmin));
Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
while (TransactionIdIsValid(parentXid))
{
previousXid = parentXid;
if (TransactionIdPrecedes(parentXid, RecentXmin))
if (TransactionIdPrecedes(parentXid, TransactionXmin))
break;
parentXid = SubTransGetParent(parentXid);
}
@ -312,7 +312,7 @@ ExtendSUBTRANS(TransactionId newestXact)
* Remove all SUBTRANS segments before the one holding the passed transaction ID
*
* This is normally called during checkpoint, with oldestXact being the
* oldest XMIN of any running transaction.
* oldest TransactionXmin of any running transaction.
*/
void
TruncateSUBTRANS(TransactionId oldestXact)