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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2007-05-30 20:12:03 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2007-05-30 20:12:03 +0000 |
| commit | d526575f893c1a4e05ebd307e80203536b213a6d (patch) | |
| tree | 529be7e5571f622bad1daab0d02de0c6669e9b81 /src/include/access/relscan.h | |
| parent | 0a6f2ee84de589e14941da640fb686c7eda7be01 (diff) | |
| download | postgresql-d526575f893c1a4e05ebd307e80203536b213a6d.tar.gz | |
Make large sequential scans and VACUUMs work in a limited-size "ring" of
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.
Diffstat (limited to 'src/include/access/relscan.h')
| -rw-r--r-- | src/include/access/relscan.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h index 7a1ea39352..200b45713e 100644 --- a/src/include/access/relscan.h +++ b/src/include/access/relscan.h @@ -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/access/relscan.h,v 1.53 2007/05/27 03:50:39 tgl Exp $ + * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.54 2007/05/30 20:12:02 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -27,6 +27,7 @@ typedef struct HeapScanDescData int rs_nkeys; /* number of scan keys */ ScanKey rs_key; /* array of scan key descriptors */ BlockNumber rs_nblocks; /* number of blocks to scan */ + BufferAccessStrategy rs_strategy; /* access strategy for reads */ bool rs_pageatatime; /* verify visibility page-at-a-time? */ /* scan current state */ |