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| author | Peter Geoghegan <pg@bowt.ie> | 2021-09-21 18:57:32 -0700 |
|---|---|---|
| committer | Peter Geoghegan <pg@bowt.ie> | 2021-09-21 18:57:32 -0700 |
| commit | dd94c2852e6e3a246b9fd64bf2d9c7fc01020905 (patch) | |
| tree | b30722ab0e1bf1d9a4e66b6481a27016ca24712c /src/backend/access/nbtree/nbtinsert.c | |
| parent | 1a9d802828110c87a207785aaf6b00d8917a86ad (diff) | |
| download | postgresql-dd94c2852e6e3a246b9fd64bf2d9c7fc01020905.tar.gz postgresql-dd94c2852e6e3a246b9fd64bf2d9c7fc01020905.zip | |
Fix "single value strategy" index deletion issue.
It is not appropriate for deduplication to apply single value strategy
when triggered by a bottom-up index deletion pass. This wastes cycles
because later bottom-up deletion passes will overinterpret older
duplicate tuples that deduplication actually just skipped over "by
design". It also makes bottom-up deletion much less effective for low
cardinality indexes that happen to cross a meaningless "index has single
key value per leaf page" threshold.
To fix, slightly narrow the conditions under which deduplication's
single value strategy is considered. We already avoided the strategy
for a unique index, since our high level goal must just be to buy time
for VACUUM to run (not to buy space). We'll now also avoid it when we
just had a bottom-up pass that reported failure. The two cases share
the same high level goal, and already overlapped significantly, so this
approach is quite natural.
Oversight in commit d168b666, which added bottom-up index deletion.
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-WznaOvM+Gyj-JQ0X=JxoMDxctDTYjiEuETdAGbF5EUc3MA@mail.gmail.com
Backpatch: 14-, where bottom-up deletion was introduced.
Diffstat (limited to 'src/backend/access/nbtree/nbtinsert.c')
| -rw-r--r-- | src/backend/access/nbtree/nbtinsert.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c index 6ac205c98ee..7355e1dba13 100644 --- a/src/backend/access/nbtree/nbtinsert.c +++ b/src/backend/access/nbtree/nbtinsert.c @@ -2748,7 +2748,7 @@ _bt_delete_or_dedup_one_page(Relation rel, Relation heapRel, /* Perform deduplication pass (when enabled and index-is-allequalimage) */ if (BTGetDeduplicateItems(rel) && itup_key->allequalimage) _bt_dedup_pass(rel, buffer, heapRel, insertstate->itup, - insertstate->itemsz, checkingunique); + insertstate->itemsz, (indexUnchanged || uniquedup)); } /* |