RE: [EXT] Re: Why using a partial index is doing slightly more logical I/O than a normal index

Thanks for the reply Jeff. Yes- more of an academic question. Regarding this part:

Index Cond: ((workflow_id = 1070) AND ((status)::text = ANY ('{NOT_STARTED,PAUSED,PENDING,RUNNING}'::text[])))
Filter: (deleted_millis <= 0)
Buffers: shared hit=24

For this usage, the =ANY is applied as an "in-index filter". It only descends the index once, to where workflow_id=1070, and then scans forward applying the =ANY to each index-tuple until it exhausts the =1070 condition. As long as all the =1070 entries fit into just a few buffers, the count of buffers accessed by doing this is fewer than doing the re-descents. (Stepping from tuple to tuple in the same index page doesn't count as a new access. While a re-descent releases and reacquires the buffer)

There are 2,981,425 rows where workflow_id = 1070. Does that change your theory of using an “in-index filter” for that plan? When you say there was a bit of speculation on the “boundard condition” vs “in-index filter” is the speculation on if Postgres has 2 different ways of processing a =ANY filter or is the speculation that one is being used by one plan and the other is being used by the other plan?

Thanks again for your reply. It is helpful.
Steve