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Don't initialize page in {vm,fsm}_extend(), not needed 

The read path needs to be able to initialize pages anyway, as relation
extensions are not durable. By avoiding initializing pages, we can, in a
future patch, extend the relation by multiple blocks at once.

Using smgrextend() for {vm,fsm}_extend() is not a good idea in general, as at
least one page of the VM/FSM will be read immediately after, always causing a
cache miss, requiring us to read content we just wrote.

Discussion: https://postgr.es/m/20230301223515.pucbj7nb54n4i4nv@awork3.anarazel.de
This commit is contained in:
Andres Freund 2023-04-05 08:19:39 -07:00
parent 86a3fc7ec8
commit 3d6a98457d
2 changed files with 2 additions and 9 deletions
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6
src/backend/access/heap/visibilitymap.c
View File

@ -622,11 +622,9 @@ static void
vm_extend(Relation rel, BlockNumber vm_nblocks)
{
BlockNumber vm_nblocks_now;
PGAlignedBlock pg;
PGAlignedBlock pg = {0};
SMgrRelation reln;
PageInit((Page) pg.data, BLCKSZ, 0);
/*
* We use the relation extension lock to lock out other backends trying to
* extend the visibility map at the same time. It also locks out extension
@ -662,8 +660,6 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
/* Now extend the file */
while (vm_nblocks_now < vm_nblocks)
{
PageSetChecksumInplace((Page) pg.data, vm_nblocks_now);
smgrextend(reln, VISIBILITYMAP_FORKNUM, vm_nblocks_now, pg.data, false);
vm_nblocks_now++;
}

5
src/backend/storage/freespace/freespace.c
View File

@ -608,10 +608,9 @@ static void
fsm_extend(Relation rel, BlockNumber fsm_nblocks)
{
BlockNumber fsm_nblocks_now;
PGAlignedBlock pg;
PGAlignedBlock pg = {0};
SMgrRelation reln;
PageInit((Page) pg.data, BLCKSZ, 0);
/*
* We use the relation extension lock to lock out other backends trying to
@ -649,8 +648,6 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
/* Extend as needed. */
while (fsm_nblocks_now < fsm_nblocks)
{
PageSetChecksumInplace((Page) pg.data, fsm_nblocks_now);
smgrextend(reln, FSM_FORKNUM, fsm_nblocks_now,
pg.data, false);
fsm_nblocks_now++;