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Make large sequential scans and VACUUMs work in a limited-size "ring" of

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buffers, rather than blowing out the whole shared-buffer arena.  Aside from
avoiding cache spoliation, this fixes the problem that VACUUM formerly tended
to cause a WAL flush for every page it modified, because we had it hacked to
use only a single buffer.  Those flushes will now occur only once per
ring-ful.  The exact ring size, and the threshold for seqscans to switch into
the ring usage pattern, remain under debate; but the infrastructure seems
done.  The key bit of infrastructure is a new optional BufferAccessStrategy
object that can be passed to ReadBuffer operations; this replaces the former
StrategyHintVacuum API.

This patch also changes the buffer usage-count methodology a bit: we now
advance usage_count when first pinning a buffer, rather than when last
unpinning it.  To preserve the behavior that a buffer's lifetime starts to
decrease when it's released, the clock sweep code is modified to not decrement
usage_count of pinned buffers.

Work not done in this commit: teach GiST and GIN indexes to use the vacuum
BufferAccessStrategy for vacuum-driven fetches.

Original patch by Simon, reworked by Heikki and again by Tom.
This commit is contained in:
Tom Lane
2007-05-30 20:12:03 +00:00
parent 0a6f2ee84d
commit d526575f89
24 changed files with 722 additions and 262 deletions
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4
src/backend/tcop/utility.c
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@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.279 2007/04/27 22:05:49 tgl Exp $
* $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.280 2007/05/30 20:12:01 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -931,7 +931,7 @@ ProcessUtility(Node *parsetree,
break;
case T_VacuumStmt:
vacuum((VacuumStmt *) parsetree, NIL, isTopLevel);
vacuum((VacuumStmt *) parsetree, NIL, NULL, isTopLevel);
break;
case T_ExplainStmt: