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Refactor checks for deleted GiST pages.

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The explicit check in gistScanPage() isn't currently really necessary, as
a deleted page is always empty, so the loop would fall through without
doing anything, anyway. But it's a marginal optimization, and it gives a
nice place to attach a comment to explain how it works.

Backpatch to v12, where GiST page deletion was introduced.

Reviewed-by: Andrey Borodin
Discussion: https://www.postgresql.org/message-id/835A15A5-F1B4-4446-A711-BF48357EB602%40yandex-team.ru
This commit is contained in:
Heikki Linnakangas
2019-07-24 20:24:05 +03:00
parent 1a721248f3
commit 9eb5607e69
2 changed files with 29 additions and 25 deletions
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14
src/backend/access/gist/gistget.c
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@ -377,6 +377,20 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
MemoryContextSwitchTo(oldcxt);
}
/*
* Check if the page was deleted after we saw the downlink. There's
* nothing of interest on a deleted page. Note that we must do this
* after checking the NSN for concurrent splits! It's possible that
* the page originally contained some tuples that are visible to us,
* but was split so that all the visible tuples were moved to another
* page, and then this page was deleted.
*/
if (GistPageIsDeleted(page))
{
UnlockReleaseBuffer(buffer);
return;
}
so->nPageData = so->curPageData = 0;
scan->xs_hitup = NULL; /* might point into pageDataCxt */
if (so->pageDataCxt)