pg prewarm seq scan #765
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pg prewarm seq scan #765
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This improves the stability of VACUUM when processing btree indexes, which was previously able to trigger an assertion failure in _bt_lock_subtree_parent() when an error was previously thrown outside the scope of _bt_split() when splitting a btree page. VACUUM would consider the index as in a corrupted state as the right page would not be zeroed for the error thrown (allocation failure is one pattern). In a non-assert build, VACUUM is able to succeed, reporting what it sees as a corruption while attempting to fix the index. This would manifest as a LOG message, as of: LOG: failed to re-find parent key in index "idx" for deletion target page N CONTEXT: while vacuuming index "idx" of relation "public.tab" This commit improves the code to rely on two PGAlignedBlocks that are used as a temporary space for the left and right pages. The main change concerns the right page, whose contents are now copied into the "temporary" PGAlignedBlock page while its original space is zeroed. Its contents are moved from the PGAlignedBlock page back to the page once we enter in the critical section used for the split. This simplifies the split logic, as it is not necessary to zero the right page before throwing an error anymore. Hence errors can now be thrown outside the split code. For the left page, this shaves one allocation, with PageGetTempPage() being previously used. The previous logic originates from commit 8fa30f9, at a point where PGAlignedBlock did not exist yet. This could be argued as something that should be backpatched, but the lack of complaints indicates that it may not be necessary. Author: Konstantin Knizhnik <[email protected]> Discussion: https://postgr.es/m/[email protected]
…into haoyu-v16
HaoyuHuang
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see https://github.com/databricks-eng/hadron/pull/2928 for details