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Commitc1458cc

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Avoid marking buffer dirty when VACUUM has no work to do.
When wal_level = 'hot_standby' we touched the last page of therelation during a VACUUM, even if nothing else had happened.That would alter the LSN of the last block and set the mtimeof the relation file unnecessarily. Noted by Thom Brown.
1 parentf6438f6 commitc1458cc

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‎src/backend/access/nbtree/nbtpage.c

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -732,7 +732,7 @@ _bt_page_recyclable(Page page)
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* and so must be scanned anyway during replay. We always write a WAL record
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* for the last block in the index, whether or not it contained any items
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* to be removed. This allows us to scan right up to end of index to
735-
* ensure correct locking.
735+
* ensure correct locking. That is the only time we are called with nitems==0.
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*/
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void
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_bt_delitems_vacuum(Relationrel,Bufferbuf,
@@ -764,7 +764,8 @@ _bt_delitems_vacuum(Relation rel, Buffer buf,
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*/
765765
opaque->btpo_flags &= ~BTP_HAS_GARBAGE;
766766

767-
MarkBufferDirty(buf);
767+
if (nitems>0)
768+
MarkBufferDirty(buf);
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769770
/* XLOG stuff */
770771
if (RelationNeedsWAL(rel))
@@ -804,8 +805,11 @@ _bt_delitems_vacuum(Relation rel, Buffer buf,
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805806
recptr=XLogInsert(RM_BTREE_ID,XLOG_BTREE_VACUUM,rdata);
806807

807-
PageSetLSN(page,recptr);
808-
PageSetTLI(page,ThisTimeLineID);
808+
if (nitems>0)
809+
{
810+
PageSetLSN(page,recptr);
811+
PageSetTLI(page,ThisTimeLineID);
812+
}
809813
}
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END_CRIT_SECTION();

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