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d526575f89
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.
47 lines
1.1 KiB
C
47 lines
1.1 KiB
C
/*-------------------------------------------------------------------------
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*
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* buf.h
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* Basic buffer manager data types.
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*
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*
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/storage/buf.h,v 1.22 2007/05/30 20:12:03 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef BUF_H
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#define BUF_H
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/*
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* Buffer identifiers.
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*
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* Zero is invalid, positive is the index of a shared buffer (1..NBuffers),
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* negative is the index of a local buffer (-1 .. -NLocBuffer).
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*/
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typedef int Buffer;
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#define InvalidBuffer 0
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/*
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* BufferIsInvalid
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* True iff the buffer is invalid.
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*/
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#define BufferIsInvalid(buffer) ((buffer) == InvalidBuffer)
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/*
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* BufferIsLocal
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* True iff the buffer is local (not visible to other backends).
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*/
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#define BufferIsLocal(buffer) ((buffer) < 0)
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/*
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* Buffer access strategy objects.
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*
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* BufferAccessStrategyData is private to freelist.c
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*/
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typedef struct BufferAccessStrategyData *BufferAccessStrategy;
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#endif /* BUF_H */
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