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Add bound check before bsearch() for performance

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In the current lazy vacuum implementation, some index AMs such as
btree indexes call lazy_tid_reaped() for each index tuple during
ambulkdelete to check if the index tuple points to the (collected)
garbage tuple.  In that function, we simply call bsearch(), but we
should be able to know the result without bsearch() if the index tuple
points to the heap tuple that is out of range of the collected garbage
tuples.  Therefore, add a simple bound check before resorting to
bsearch().  Testing has shown that this can give significant
performance benefits.

Author: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+fd4k76j8jKzJzcx8UqEugvayaMSnQz0iLUt_XgBp-_-bd22A@mail.gmail.com
This commit is contained in:
Peter Eisentraut 2021-03-10 15:19:37 +01:00
parent c427de427a
commit bbaf315309
1 changed files with 17 additions and 0 deletions
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17
src/backend/access/heap/vacuumlazy.c
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@ -61,6 +61,7 @@
#include "access/visibilitymap.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/index.h"
#include "catalog/storage.h"
#include "commands/dbcommands.h"
#include "commands/progress.h"
@ -2923,8 +2924,24 @@ static bool
lazy_tid_reaped(ItemPointer itemptr, void *state)
{
LVDeadTuples *dead_tuples = (LVDeadTuples *) state;
int64 litem,
ritem,
item;
ItemPointer res;
litem = itemptr_encode(&dead_tuples->itemptrs[0]);
ritem = itemptr_encode(&dead_tuples->itemptrs[dead_tuples->num_tuples - 1]);
item = itemptr_encode(itemptr);
/*
* Doing a simple bound check before bsearch() is useful to avoid the
* extra cost of bsearch(), especially if dead tuples on the heap are
* concentrated in a certain range. Since this function is called for
* every index tuple, it pays to be really fast.
*/
if (item < litem || item > ritem)
return false;
res = (ItemPointer) bsearch((void *) itemptr,
(void *) dead_tuples->itemptrs,
dead_tuples->num_tuples,