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Optimise btree delete processing when no active backends.

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Clarify comments, downgrade a message to DEBUG and remove some
debug counters. Direct from ideas by Heikki Linnakangas.
This commit is contained in:
Simon Riggs
2010-04-22 08:04:25 +00:00
parent 781ec6b75d
commit a2555571fb
3 changed files with 22 additions and 23 deletions
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34
src/backend/access/nbtree/nbtxlog.c
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@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.66 2010/04/19 17:54:48 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.67 2010/04/22 08:04:24 sriggs Exp $
*
*-------------------------------------------------------------------------
*/
@ -578,9 +578,17 @@ btree_xlog_delete_get_latestRemovedXid(XLogRecord *record)
OffsetNumber hoffnum;
TransactionId latestRemovedXid = InvalidTransactionId;
TransactionId htupxid = InvalidTransactionId;
int num_unused = 0, num_redirect = 0, num_dead = 0;
int i;
/*
* If there's nothing running on the standby we don't need to derive
* a full latestRemovedXid value, so use a fast path out of here.
* That returns InvalidTransactionId, and so will conflict with
* users, but since we just worked out that's zero people, its OK.
*/
if (CountDBBackends(InvalidOid) == 0)
return latestRemovedXid;
/*
* Get index page
*/
@ -629,7 +637,6 @@ btree_xlog_delete_get_latestRemovedXid(XLogRecord *record)
*/
while (ItemIdIsRedirected(hitemid))
{
num_redirect++;
hoffnum = ItemIdGetRedirect(hitemid);
hitemid = PageGetItemId(hpage, hoffnum);
CHECK_FOR_INTERRUPTS();
@ -662,25 +669,23 @@ btree_xlog_delete_get_latestRemovedXid(XLogRecord *record)
* marked on LP_NORMAL items. So we just ignore this item and move
* onto the next, for the purposes of calculating latestRemovedxids.
*/
num_dead++;
}
else
{
Assert(!ItemIdIsUsed(hitemid));
num_unused++;
}
UnlockReleaseBuffer(hbuffer);
}
UnlockReleaseBuffer(ibuffer);
Assert(num_unused == 0);
/*
* Note that if all heap tuples were LP_DEAD then we will be
* returning InvalidTransactionId here. This seems very unlikely
* in practice.
* returning InvalidTransactionId here. That can happen if we are
* re-replaying this record type, though that will be before the
* consistency point and will not cause problems. It should
* happen very rarely after the consistency point, though note
* that we can't tell the difference between this and the fast
* path exit above. May need to change that in future.
*/
return latestRemovedXid;
}
@ -963,13 +968,6 @@ btree_redo(XLogRecPtr lsn, XLogRecord *record)
TransactionId latestRemovedXid = btree_xlog_delete_get_latestRemovedXid(record);
xl_btree_delete *xlrec = (xl_btree_delete *) XLogRecGetData(record);
/*
* XXX Currently we put everybody on death row, because
* currently _bt_delitems() supplies InvalidTransactionId.
* This can be fairly painful, so providing a better value
* here is worth some thought and possibly some effort to
* improve.
*/
ResolveRecoveryConflictWithSnapshot(latestRemovedXid, xlrec->node);
}
break;