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Commit7bb9721

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Save a few cycles during nbtree VACUUM.
Avoid calling RelationGetNumberOfBlocks() unnecessarily in the commoncase where there are no deleted but not yet recycled pages to recycleduring a cleanup-only nbtree VACUUM operation.Follow-up to commite5d8a99, which (among other things) taught the"skip full scan" nbtree VACUUM mechanism to only trigger a full indexscan when the absolute number of deleted pages in the index isconsidered excessive.
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‎src/backend/access/nbtree/nbtree.c

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Original file line numberDiff line numberDiff line change
@@ -825,9 +825,10 @@ _bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
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* calls. That is, we can end up scanning the entire index without ever
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* placing even 1 of the prev_num_delpages pages in the free space map, at
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* least in certain narrow cases (see nbtree/README section on recycling
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* deleted pages for details). This rarelymatters in practice.
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* deleted pages for details). This rarelycomes up in practice.
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*/
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if (prev_num_delpages>RelationGetNumberOfBlocks(info->index) /20)
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if (prev_num_delpages>0&&
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prev_num_delpages>RelationGetNumberOfBlocks(info->index) /20)
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return true;
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return false;
@@ -916,17 +917,12 @@ btvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
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}
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/*
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* By here, we know for sure that this VACUUM operation won't be skipping
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* its btvacuumscan() call. Maintain num_delpages value in metapage.
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* This information will be used by _bt_vacuum_needs_cleanup() during
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* future VACUUM operations that don't need to call btbulkdelete().
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* Maintain num_delpages value in metapage for _bt_vacuum_needs_cleanup().
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*
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* num_delpages is the number of deleted pages now in the index that were
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* not safe to place in the FSM to be recycled just yet. We expect that
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* it will almost certainly be possible to place all of these pages in the
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* FSM during the next VACUUM operation. _bt_vacuum_needs_cleanup() will
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* force the next VACUUM to consider this before allowing btvacuumscan()
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* to be skipped entirely.
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* FSM during the next VACUUM operation.
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*/
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Assert(stats->pages_deleted >=stats->pages_free);
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num_delpages=stats->pages_deleted-stats->pages_free;

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