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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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18
src/backend/commands/vacuumlazy.c
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@@ -36,7 +36,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.89 2007/05/17 15:28:29 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.90 2007/05/30 20:11:57 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -96,11 +96,14 @@ typedef struct LVRelStats
} LVRelStats;
/* A few variables that don't seem worth passing around as parameters */
static int elevel = -1;
static TransactionId OldestXmin;
static TransactionId FreezeLimit;
static BufferAccessStrategy vac_strategy;
/* non-export function prototypes */
static void lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
@@ -138,7 +141,8 @@ static int vac_cmp_page_spaces(const void *left, const void *right);
* and locked the relation.
*/
void
lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
BufferAccessStrategy bstrategy)
{
LVRelStats *vacrelstats;
Relation *Irel;
@@ -158,6 +162,8 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
else
elevel = DEBUG2;
vac_strategy = bstrategy;
vacuum_set_xid_limits(vacstmt->freeze_min_age, onerel->rd_rel->relisshared,
&OldestXmin, &FreezeLimit);
@@ -318,7 +324,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
vacrelstats->num_index_scans++;
}
buf = ReadBuffer(onerel, blkno);
buf = ReadBufferWithStrategy(onerel, blkno, vac_strategy);
/* Initially, we only need shared access to the buffer */
LockBuffer(buf, BUFFER_LOCK_SHARE);
@@ -586,7 +592,7 @@ lazy_vacuum_heap(Relation onerel, LVRelStats *vacrelstats)
vacuum_delay_point();
tblk = ItemPointerGetBlockNumber(&vacrelstats->dead_tuples[tupindex]);
buf = ReadBuffer(onerel, tblk);
buf = ReadBufferWithStrategy(onerel, tblk, vac_strategy);
LockBufferForCleanup(buf);
tupindex = lazy_vacuum_page(onerel, tblk, buf, tupindex, vacrelstats);
/* Now that we've compacted the page, record its available space */
@@ -684,6 +690,7 @@ lazy_vacuum_index(Relation indrel,
ivinfo.message_level = elevel;
/* We don't yet know rel_tuples, so pass -1 */
ivinfo.num_heap_tuples = -1;
ivinfo.strategy = vac_strategy;
/* Do bulk deletion */
*stats = index_bulk_delete(&ivinfo, *stats,
@@ -713,6 +720,7 @@ lazy_cleanup_index(Relation indrel,
ivinfo.vacuum_full = false;
ivinfo.message_level = elevel;
ivinfo.num_heap_tuples = vacrelstats->rel_tuples;
ivinfo.strategy = vac_strategy;
stats = index_vacuum_cleanup(&ivinfo, stats);
@@ -869,7 +877,7 @@ count_nondeletable_pages(Relation onerel, LVRelStats *vacrelstats)
blkno--;
buf = ReadBuffer(onerel, blkno);
buf = ReadBufferWithStrategy(onerel, blkno, vac_strategy);
/* In this phase we only need shared access to the buffer */
LockBuffer(buf, BUFFER_LOCK_SHARE);