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Heikki Linnakangas 28d3c2ddcf Fix another bug in parent page splitting during GiST index build. Yet another bug in the ilk of commits `a7ee7c851` and `741b88435`. In `741b88435`, we took care to clear the memorized location of the downlink when we split the parent page, because splitting the parent page can move the downlink. But we missed that even updating a tuple on the parent can move it, because updating a tuple on a gist page is implemented as a delete+insert, so the updated tuple gets moved to the end of the page. This commit fixes the bug in two different ways (belt and suspenders): 1. Clear the downlink when we update a tuple on the parent page, even if it's not split. This the same approach as in commits `a7ee7c851` and `741b88435`. I also noticed that gistFindCorrectParent did not clear the 'downlinkoffnum' when it stepped to the right sibling. Fix that too, as it seems like a clear bug even though I haven't been able to find a test case to hit that. 2. Change gistFindCorrectParent so that it treats 'downlinkoffnum' merely as a hint. It now always first checks if the downlink is still at that location, and if not, it scans the page like before. That's more robust if there are still more cases where we fail to clear 'downlinkoffnum' that we haven't yet uncovered. With this, it's no longer necessary to meticulously clear 'downlinkoffnum', so this makes the previous fixes unnecessary, but I didn't revert them because it still seems nice to clear it when we know that the downlink has moved. Also add the test case using the same test data that Alexander posted. I tried to reduce it to a smaller test, and I also tried to reproduce this with different test data, but I was not able to, so let's just include what we have. Backpatch to v12, like the previous fixes. Reported-by: Alexander Lakhin Discussion: https://www.postgresql.org/message-id/18129-caca016eaf0c3702@postgresql.org	2 years ago
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_int.sql	Fix another bug in parent page splitting during GiST index build.	2 years ago

Heikki Linnakangas 28d3c2ddcf Fix another bug in parent page splitting during GiST index build.

Yet another bug in the ilk of commits a7ee7c851 and 741b88435. In
741b88435, we took care to clear the memorized location of the
downlink when we split the parent page, because splitting the parent
page can move the downlink. But we missed that even *updating* a tuple
on the parent can move it, because updating a tuple on a gist page is
implemented as a delete+insert, so the updated tuple gets moved to the
end of the page.

This commit fixes the bug in two different ways (belt and suspenders):

1. Clear the downlink when we update a tuple on the parent page, even
   if it's not split. This the same approach as in commits a7ee7c851
   and 741b88435.

   I also noticed that gistFindCorrectParent did not clear the
   'downlinkoffnum' when it stepped to the right sibling. Fix that
   too, as it seems like a clear bug even though I haven't been able
   to find a test case to hit that.

2. Change gistFindCorrectParent so that it treats 'downlinkoffnum'
   merely as a hint. It now always first checks if the downlink is
   still at that location, and if not, it scans the page like before.
   That's more robust if there are still more cases where we fail to
   clear 'downlinkoffnum' that we haven't yet uncovered. With this,
   it's no longer necessary to meticulously clear 'downlinkoffnum',
   so this makes the previous fixes unnecessary, but I didn't revert
   them because it still seems nice to clear it when we know that the
   downlink has moved.

Also add the test case using the same test data that Alexander
posted. I tried to reduce it to a smaller test, and I also tried to
reproduce this with different test data, but I was not able to, so
let's just include what we have.

Backpatch to v12, like the previous fixes.

Reported-by: Alexander Lakhin
Discussion: https://www.postgresql.org/message-id/18129-caca016eaf0c3702@postgresql.org

2 years ago

_int.sql Fix another bug in parent page splitting during GiST index build. 2 years ago