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Avoid marking buffer dirty when VACUUM has no work to do.

author Simon Riggs <simon@2ndQuadrant.com>

2011年11月18日 16:06:53 +0000 (16:06 +0000)

committer Simon Riggs <simon@2ndQuadrant.com>

2011年11月18日 16:06:53 +0000 (16:06 +0000)

When wal_level = 'hot_standby' we touched the last page of the
relation during a VACUUM, even if nothing else had happened.
That would alter the LSN of the last block and set the mtime
of the relation file unnecessarily. Noted by Thom Brown.

src/backend/access/nbtree/nbtpage.c patch | blob | blame | history

diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c

index f9b3e1feafe62130e250f68b2183cdf5f944d19b..6f6e676ec08791689a049c7b2a556f2670a7a5b4 100644 (file)

--- a/src/backend/access/nbtree/nbtpage.c

+++ b/src/backend/access/nbtree/nbtpage.c

@@ -732,7 +732,7 @@ _bt_page_recyclable(Page page)

* and so must be scanned anyway during replay. We always write a WAL record

* for the last block in the index, whether or not it contained any items

* to be removed. This allows us to scan right up to end of index to

- * ensure correct locking.

+ * ensure correct locking. That is the only time we are called with nitems==0.

void

_bt_delitems_vacuum(Relation rel, Buffer buf,

@@ -764,7 +764,8 @@ _bt_delitems_vacuum(Relation rel, Buffer buf,

opaque->btpo_flags &= ~BTP_HAS_GARBAGE;

- MarkBufferDirty(buf);

+ if (nitems > 0)

+ MarkBufferDirty(buf);

/* XLOG stuff */

if (RelationNeedsWAL(rel))

@@ -804,8 +805,11 @@ _bt_delitems_vacuum(Relation rel, Buffer buf,

recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_VACUUM, rdata);

- PageSetLSN(page, recptr);

- PageSetTLI(page, ThisTimeLineID);

+ if (nitems > 0)

+ {

+ PageSetLSN(page, recptr);

+ PageSetTLI(page, ThisTimeLineID);

+ }

}

END_CRIT_SECTION();

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