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Assert consistency of currPage that ended scan.

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When _bt_readnextpage is called with our nbtree parallel scan already
seized (i.e. when it is directly called by _bt_first), we never expect a
prior call to _bt_readpage for lastcurrblkno to already indicate that
the scan should end -- the _bt_first caller's blkno must always be read.
After all, the "prior" _bt_readpage call (the call for lastcurrblkno)
probably took place in some other backend (and it might not even have
finished by the time our backend reaches _bt_first/_bt_readnextpage).

Add a documenting assertion to the path where _bt_readnextpage ends the
parallel scan based on information about lastcurrblkno from so->currPos.
Assert that the most recent _bt_readpage call that set so->currPos is in
fact lastcurrblkno's _bt_readpage call.

Follow-up to bugfix commit b5ee4e52.
This commit is contained in:
Peter Geoghegan
2024-11-08 16:34:41 -05:00
parent 4225276e25
commit caca6d8d27
1 changed files with 2 additions and 1 deletions
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3
src/backend/access/nbtree/nbtsearch.c
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@@ -2230,8 +2230,9 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno,
!so->currPos.moreRight : !so->currPos.moreLeft)) !so->currPos.moreRight : !so->currPos.moreLeft))
{ {
/* most recent _bt_readpage call (for lastcurrblkno) ended scan */ /* most recent _bt_readpage call (for lastcurrblkno) ended scan */
Assert(so->currPos.currPage == lastcurrblkno && !seized);
BTScanPosInvalidate(so->currPos); BTScanPosInvalidate(so->currPos);
_bt_parallel_done(scan); _bt_parallel_done(scan); /* iff !so->needPrimScan */
return false; return false;
} }