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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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13
src/include/commands/vacuum.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/commands/vacuum.h,v 1.71 2007/05/17 15:28:29 alvherre Exp $
* $PostgreSQL: pgsql/src/include/commands/vacuum.h,v 1.72 2007/05/30 20:12:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -18,9 +18,11 @@
#include "catalog/pg_statistic.h"
#include "catalog/pg_type.h"
#include "nodes/parsenodes.h"
#include "storage/buf.h"
#include "storage/lock.h"
#include "utils/rel.h"
/*----------
* ANALYZE builds one of these structs for each attribute (column) that is
* to be analyzed. The struct and subsidiary data are in anl_context,
@@ -110,7 +112,8 @@ extern int vacuum_freeze_min_age;
/* in commands/vacuum.c */
extern void vacuum(VacuumStmt *vacstmt, List *relids, bool isTopLevel);
extern void vacuum(VacuumStmt *vacstmt, List *relids,
BufferAccessStrategy bstrategy, bool isTopLevel);
extern void vac_open_indexes(Relation relation, LOCKMODE lockmode,
int *nindexes, Relation **Irel);
extern void vac_close_indexes(int nindexes, Relation *Irel, LOCKMODE lockmode);
@@ -127,9 +130,11 @@ extern bool vac_is_partial_index(Relation indrel);
extern void vacuum_delay_point(void);
/* in commands/vacuumlazy.c */
extern void lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
extern void lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
BufferAccessStrategy bstrategy);
/* in commands/analyze.c */
extern void analyze_rel(Oid relid, VacuumStmt *vacstmt);
extern void analyze_rel(Oid relid, VacuumStmt *vacstmt,
BufferAccessStrategy bstrategy);
#endif /* VACUUM_H */