On Fri, Mar 24, 2023 at 08:00:44PM -0700, Andres Freund wrote: > I don't understand what we're optimizing for here. These functions are very > very very far from being a hot path. The xact functions are barely ever > used. Compared to the cost of query evaluation the cost of iterating throught > he subxacts is neglegible.
I was wondering about that, and I see why I'm wrong. I have quickly gone up to 10k subtransactions, and while I was seeing what looks like difference of 8~10% in runtime when looking at pg_stat_xact_all_tables, the overval runtime was still close enough (5.8ms vs 6.4ms). At this scale, possible that it was some noise, these seemed repeatable still not to worry about. Anyway, I was looking at this patch, and I still feel that it is a bit incorrect to have the copy of PgStat_TableStatus returned by find_tabstat_entry() to point to the same list of subtransaction data as the pending entry found, while the counters are incremented. This could lead to mistakes if the copy from find_tabstat_entry() is used in an unexpected way in the future. The current callers are OK, but this does not give me a warm feeling :/ -- Michael
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