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Improve handling of prune/no-prune decisions by storing a page's oldest

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unpruned XMAX in its header.  At the cost of 4 bytes per page, this keeps us
from performing heap_page_prune when there's no chance of pruning anything.
Seems to be necessary per Heikki's preliminary performance testing.
This commit is contained in:
Tom Lane
2007-09-21 21:25:42 +00:00
parent 386a5d4268
commit cc59049daf
10 changed files with 92 additions and 59 deletions
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27
src/backend/access/heap/pruneheap.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/heap/pruneheap.c,v 1.1 2007/09/20 17:56:30 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/heap/pruneheap.c,v 1.2 2007/09/21 21:25:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -63,9 +63,10 @@ heap_page_prune_opt(Relation relation, Buffer buffer, TransactionId OldestXmin)
/*
* Let's see if we really need pruning.
*
* Forget it if page is not hinted to contain something prunable
* Forget it if page is not hinted to contain something prunable that's
* older than OldestXmin.
*/
if (!PageIsPrunable(dp))
if (!PageIsPrunable(dp, OldestXmin))
return;
/*
@ -93,6 +94,8 @@ heap_page_prune_opt(Relation relation, Buffer buffer, TransactionId OldestXmin)
/*
* Now that we have buffer lock, get accurate information about the
* page's free space, and recheck the heuristic about whether to prune.
* (We needn't recheck PageIsPrunable, since no one else could have
* pruned while we hold pin.)
*/
if (PageIsFull(dp) || PageGetHeapFreeSpace((Page) dp) < minfree)
{
@ -147,7 +150,7 @@ heap_page_prune(Relation relation, Buffer buffer, TransactionId OldestXmin,
START_CRIT_SECTION();
/*
* Mark the page as clear of prunable tuples. If we find a tuple which
* Mark the page as clear of prunable tuples. If we find a tuple which
* may soon become prunable, we shall set the hint again. Also clear
* the "page is full" flag, since there's no point in repeating the
* prune/defrag process until something else happens to the page.
@ -203,6 +206,14 @@ heap_page_prune(Relation relation, Buffer buffer, TransactionId OldestXmin,
PageSetLSN(BufferGetPage(buffer), recptr);
}
}
else
{
/*
* If we didn't prune anything, we have nonetheless updated the
* pd_prune_xid field; treat this as a non-WAL-logged hint.
*/
SetBufferCommitInfoNeedsSave(buffer);
}
END_CRIT_SECTION();
@ -392,18 +403,18 @@ heap_prune_chain(Relation relation, Buffer buffer, OffsetNumber rootoffnum,
case HEAPTUPLE_RECENTLY_DEAD:
recent_dead = true;
/*
* This tuple may soon become DEAD. Re-set the hint bit so
* This tuple may soon become DEAD. Update the hint field so
* that the page is reconsidered for pruning in future.
*/
PageSetPrunable(dp);
PageSetPrunable(dp, HeapTupleHeaderGetXmax(htup));
break;
case HEAPTUPLE_DELETE_IN_PROGRESS:
/*
* This tuple may soon become DEAD. Re-set the hint bit so
* This tuple may soon become DEAD. Update the hint field so
* that the page is reconsidered for pruning in future.
*/
PageSetPrunable(dp);
PageSetPrunable(dp, HeapTupleHeaderGetXmax(htup));
break;
case HEAPTUPLE_LIVE: