On Mon, Jun 21, 2021 at 5:31 AM Simon Riggs <simon.ri...@enterprisedb.com> wrote: > Seems like we can skip the uniqueness check if indexUnchanged, which > will speed up non-HOT UPDATEs on tables with B-Trees.
I thought about doing this myself. Never got as far as thinking about the correctness implications in detail. One thing that I'm concerned about is LP_DEAD bit setting inside _bt_check_unique(), which isn't going to take place when the optimization from the patch is applied. That definitely used to be way more important than kill_prior_tuple-based LP_DEAD bit setting, which has real problems with non-HOT updates [1]. _bt_check_unique() clearly makes up for that in the case of unique indexes, at least for many years. On the other hand my thinking here might well be outdated, because of course bottom-up index deletion exists now. You're using indexUnchanged here, which is used to trigger bottom-up index deletion passes. Maybe that's enough for it to not matter now, meaning that the LP_DEAD bit stuff is not a real blocker here. Offhand I'm quite unsure. [1] https://www.postgresql.org/message-id/flat/CAH2-Wz%3DSfAKVMv1x9Jh19EJ8am8TZn9f-yECipS9HrrRqSswnA%40mail.gmail.com#b20ead9675225f12b6a80e53e19eed9d -- Peter Geoghegan
