mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-09-03 11:47:20 +02:00
Fix GIN data page split ratio calculation.
The code that tried to split a page at 75/25 ratio, when appending to the end of an index, was buggy in two ways. First, there was a silly typo that caused it to just fill the left page as full as possible. But the logic as it was intended wasn't correct either, and would actually have given a ratio closer to 60/40 than 75/25. Gaetano Mendola spotted the typo. Backpatch to 9.4, where this code was added.
This commit is contained in:
parent
1c603198a4
commit
79ee6370ee
@ -622,9 +622,9 @@ dataPlaceToPageLeaf(GinBtree btree, Buffer buf, GinBtreeStack *stack,
|
||||
/*
|
||||
* Had to split.
|
||||
*
|
||||
* We already divided the segments between the left and the right
|
||||
* page. The left page was filled as full as possible, and the rest
|
||||
* overflowed to the right page. When building a new index, that's
|
||||
* leafRepackItems already divided the segments between the left and
|
||||
* the right page. It filled the left page as full as possible, and
|
||||
* put the rest to the right page. When building a new index, that's
|
||||
* good, because the table is scanned from beginning to end and there
|
||||
* won't be any more insertions to the left page during the build.
|
||||
* This packs the index as tight as possible. But otherwise, split
|
||||
@ -632,9 +632,10 @@ dataPlaceToPageLeaf(GinBtree btree, Buffer buf, GinBtreeStack *stack,
|
||||
* until they're balanced.
|
||||
*
|
||||
* As a further heuristic, when appending items to the end of the
|
||||
* page, split 75/25, one the assumption that subsequent insertions
|
||||
* will probably also go to the end. This packs the index somewhat
|
||||
* tighter when appending to a table, which is very common.
|
||||
* page, try make the left page 75% full, one the assumption that
|
||||
* subsequent insertions will probably also go to the end. This packs
|
||||
* the index somewhat tighter when appending to a table, which is very
|
||||
* common.
|
||||
*/
|
||||
if (!btree->isBuild)
|
||||
{
|
||||
@ -646,14 +647,18 @@ dataPlaceToPageLeaf(GinBtree btree, Buffer buf, GinBtreeStack *stack,
|
||||
if (lastleftinfo->action != GIN_SEGMENT_DELETE)
|
||||
{
|
||||
segsize = SizeOfGinPostingList(lastleftinfo->seg);
|
||||
|
||||
/*
|
||||
* Note that we check that the right page doesn't become
|
||||
* more full than the left page even when appending. It's
|
||||
* possible that we added enough items to make both pages
|
||||
* more than 75% full.
|
||||
*/
|
||||
if ((leaf->lsize - segsize) - (leaf->rsize + segsize) < 0)
|
||||
break;
|
||||
if (append)
|
||||
{
|
||||
if ((leaf->lsize - segsize) - (leaf->lsize - segsize) < BLCKSZ / 4)
|
||||
break;
|
||||
}
|
||||
else
|
||||
{
|
||||
if ((leaf->lsize - segsize) - (leaf->rsize + segsize) < 0)
|
||||
if ((leaf->lsize - segsize) < (BLCKSZ * 3) / 4)
|
||||
break;
|
||||
}
|
||||
|
||||
|
Loading…
Reference in New Issue
Block a user