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 <[email protected]> Discussion: https://postgr.es/m/CAH2-WznaOvM+Gyj-JQ0X=jxomdxctdtyjieuetdagbf5euc...@mail.gmail.com Backpatch: 14-, where bottom-up deletion was introduced. Branch ------ REL_14_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/e665129c4727004e7a7c12c86d077abc750b3307 Modified Files -------------- src/backend/access/nbtree/nbtdedup.c | 36 +++++++++++++++++------------------ src/backend/access/nbtree/nbtinsert.c | 2 +- src/include/access/nbtree.h | 2 +- 3 files changed, 19 insertions(+), 21 deletions(-)
