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Delete empty pages during GiST VACUUM.

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To do this, we scan GiST two times. In the first pass we make note of
empty leaf pages and internal pages. At second pass we scan through
internal pages, looking for downlinks to the empty pages.

Deleting internal pages is still not supported, like in nbtree, the last
child of an internal page is never deleted. That means that if you have a
workload where new keys are always inserted to different area than where
old keys are removed, the index will still grow without bound. But the rate
of growth will be an order of magnitude slower than before.

Author: Andrey Borodin
Discussion: https://www.postgresql.org/message-id/B1E4DF12-6CD3-4706-BDBD-BF3283328F60@yandex-team.ru
This commit is contained in:
Heikki Linnakangas
2019-03-22 13:21:20 +02:00
parent df816f6ad5
commit 7df159a620
11 changed files with 626 additions and 49 deletions
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15
src/backend/access/gist/gist.c
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@ -704,6 +704,9 @@ gistdoinsert(Relation r, IndexTuple itup, Size freespace,
GISTInsertStack *item;
OffsetNumber downlinkoffnum;
/* currently, internal pages are never deleted */
Assert(!GistPageIsDeleted(stack->page));
downlinkoffnum = gistchoose(state.r, stack->page, itup, giststate);
iid = PageGetItemId(stack->page, downlinkoffnum);
idxtuple = (IndexTuple) PageGetItem(stack->page, iid);
@ -838,6 +841,18 @@ gistdoinsert(Relation r, IndexTuple itup, Size freespace,
}
}
/*
* The page might have been deleted after we scanned the parent
* and saw the downlink.
*/
if (GistPageIsDeleted(stack->page))
{
UnlockReleaseBuffer(stack->buffer);
xlocked = false;
state.stack = stack = stack->parent;
continue;
}
/* now state.stack->(page, buffer and blkno) points to leaf page */
gistinserttuple(&state, stack, giststate, itup,