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Commit5853662

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Reduce the size of memory allocations by lazy vacuum when processing a small
table, by allocating just enough for a hardcoded number of dead tuples perpage. The current estimate is 200 dead tuples per page.Per reports from Jeff Amiel, Erik Jones and Marko Kreen, and subsequentdiscussion.CVS: ----------------------------------------------------------------------CVS: Enter Log. Lines beginning with `CVS:' are removed automaticallyCVS:CVS: Committing in .CVS:CVS: Modified Files:CVS: commands/vacuumlazy.cCVS: ----------------------------------------------------------------------
1 parent48f7e64 commit5853662

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‎src/backend/commands/vacuumlazy.c

Lines changed: 18 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -11,10 +11,12 @@
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* on the number of tuples and pages we will keep track of at once.
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*
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* We are willing to use at most maintenance_work_mem memory space to keep
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* track of dead tuples. We initially allocate an array of TIDs of that size.
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* If the array threatens to overflow, we suspend the heap scan phase and
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* perform a pass of index cleanup and page compaction, then resume the heap
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* scan with an empty TID array.
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* track of dead tuples. We initially allocate an array of TIDs of that size,
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* with an upper limit that depends on table size (this limit ensures we don't
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* allocate a huge area uselessly for vacuuming small tables). If the array
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* threatens to overflow, we suspend the heap scan phase and perform a pass of
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* index cleanup and page compaction, then resume the heap scan with an empty
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* TID array.
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*
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* We can limit the storage for page free space to MaxFSMPages entries,
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* since that's the most the free space map will be willing to remember
@@ -36,7 +38,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.99 2007/09/24 03:12:23 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.100 2007/09/24 03:52:55 alvherre Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -68,6 +70,12 @@
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#defineREL_TRUNCATE_MINIMUM1000
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#defineREL_TRUNCATE_FRACTION16
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/*
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* Guesstimation of number of dead tuples per page. This is used to
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* provide an upper limit to memory allocated when vacuuming small
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* tables.
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*/
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#defineLAZY_ALLOC_TUPLES200
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typedefstructLVRelStats
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{
@@ -1001,6 +1009,11 @@ lazy_space_alloc(LVRelStats *vacrelstats, BlockNumber relblocks)
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maxtuples= (maintenance_work_mem*1024L) /sizeof(ItemPointerData);
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maxtuples=Min(maxtuples,INT_MAX);
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maxtuples=Min(maxtuples,MaxAllocSize /sizeof(ItemPointerData));
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/* curious coding here to ensure the multiplication can't overflow */
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if ((BlockNumber) (maxtuples /LAZY_ALLOC_TUPLES)>relblocks)
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maxtuples=relblocks*LAZY_ALLOC_TUPLES;
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/* stay sane if small maintenance_work_mem */
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maxtuples=Max(maxtuples,MaxHeapTuplesPerPage);
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}

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