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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/storage/buf_internals.h
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@@ -8,7 +8,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/buf_internals.h,v 1.89 2007/01/05 22:19:57 momjian Exp $
* $PostgreSQL: pgsql/src/include/storage/buf_internals.h,v 1.90 2007/05/30 20:12:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -167,9 +167,6 @@ extern DLLIMPORT BufferDesc *BufferDescriptors;
/* in localbuf.c */
extern BufferDesc *LocalBufferDescriptors;
/* in freelist.c */
extern bool strategy_hint_vacuum;
/* event counters in buf_init.c */
extern long int ReadBufferCount;
extern long int ReadLocalBufferCount;
@@ -184,8 +181,12 @@ extern long int LocalBufferFlushCount;
*/
/* freelist.c */
extern volatile BufferDesc *StrategyGetBuffer(void);
extern void StrategyFreeBuffer(volatile BufferDesc *buf, bool at_head);
extern volatile BufferDesc *StrategyGetBuffer(BufferAccessStrategy strategy,
bool *lock_held);
extern void StrategyFreeBuffer(volatile BufferDesc *buf);
extern bool StrategyRejectBuffer(BufferAccessStrategy strategy,
volatile BufferDesc *buf);
extern int StrategySyncStart(void);
extern Size StrategyShmemSize(void);
extern void StrategyInitialize(bool init);