alt Hacker NewsWhy are you using hash indexes? They're much less widely used than standard B-Tree indexes. The bucket split code likely isn't very scalable [1].
I suggest testing the same workload with your existing hash indexes replaced with equivalent B-Trees.
[1] https://github.com/postgres/postgres/blob/master/src/backend...
Last time I almost used a hash index in Postgres, I learned it was an incomplete feature and not crash-safe yet. This was v9.3? At that same time, MySQL had them and they were ok to use.
Later that got fixed, but I haven't tried again since, just been using btree because it seemed like Postgres favored that and it has theoretical advantages too.