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Reduce the size of memory allocations by lazy vacuum when processing a small

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table, by allocating just enough for a hardcoded number of dead tuples per
page.  The current estimate is 200 dead tuples per page.

Per reports from Jeff Amiel, Erik Jones and Marko Kreen, and subsequent
discussion.
CVS: ----------------------------------------------------------------------
CVS: Enter Log.  Lines beginning with `CVS:' are removed automatically
CVS:
CVS: Committing in .
CVS:
CVS: Modified Files:
CVS: 	commands/vacuumlazy.c
CVS: ----------------------------------------------------------------------
This commit is contained in:
Alvaro Herrera 2007-09-24 03:52:55 +00:00
parent 48f7e64395
commit 5853662630
1 changed files with 18 additions and 5 deletions
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23
src/backend/commands/vacuumlazy.c
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@ -11,10 +11,12 @@
* on the number of tuples and pages we will keep track of at once.
*
* We are willing to use at most maintenance_work_mem memory space to keep
* track of dead tuples. We initially allocate an array of TIDs of that size.
* If the array threatens to overflow, we suspend the heap scan phase and
* perform a pass of index cleanup and page compaction, then resume the heap
* scan with an empty TID array.
* track of dead tuples. We initially allocate an array of TIDs of that size,
* with an upper limit that depends on table size (this limit ensures we don't
* allocate a huge area uselessly for vacuuming small tables). If the array
* threatens to overflow, we suspend the heap scan phase and perform a pass of
* index cleanup and page compaction, then resume the heap scan with an empty
* TID array.
*
* We can limit the storage for page free space to MaxFSMPages entries,
* since that's the most the free space map will be willing to remember
@ -36,7 +38,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.99 2007/09/24 03:12:23 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.100 2007/09/24 03:52:55 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -68,6 +70,12 @@
#define REL_TRUNCATE_MINIMUM 1000
#define REL_TRUNCATE_FRACTION 16
/*
* Guesstimation of number of dead tuples per page. This is used to
* provide an upper limit to memory allocated when vacuuming small
* tables.
*/
#define LAZY_ALLOC_TUPLES 200
typedef struct LVRelStats
{
@ -1001,6 +1009,11 @@ lazy_space_alloc(LVRelStats *vacrelstats, BlockNumber relblocks)
maxtuples = (maintenance_work_mem * 1024L) / sizeof(ItemPointerData);
maxtuples = Min(maxtuples, INT_MAX);
maxtuples = Min(maxtuples, MaxAllocSize / sizeof(ItemPointerData));
/* curious coding here to ensure the multiplication can't overflow */
if ((BlockNumber) (maxtuples / LAZY_ALLOC_TUPLES) > relblocks)
maxtuples = relblocks * LAZY_ALLOC_TUPLES;
/* stay sane if small maintenance_work_mem */
maxtuples = Max(maxtuples, MaxHeapTuplesPerPage);
}