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Alternatives to `EXPLAIN ANALYZE` for queries that won't complete
I have a large and complex PostgreSQL
SELECT query that I would like to make faster.
EXPLAIN suggests it should run quickly, with the worst parts being scans of a few thousand rows. When run, it does not complete in any reasonable amount of time (if
statement_timeout is set to infinite, it eventually still gives up, complaining about having exceeded temporary file size limits, suggesting something is loading way more data than expected).
Usually, this would suggest to me that
EXPLAIN's estimates are horribly inaccurate in some way, and I would try
EXPLAIN ANALYZE to see what's really happening. But since this particular query is so bad I can't run it at all, I also can't run it with
What other tools are at my disposal for this sort of situation? Can I ask PostgreSQL for some sort of partial or time-limited
EXPLAIN ANALYZE, as in "run this for five minutes, then stop and tell me what you spent those five minutes doing"? If I start commenting out bits of the query until it goes fast again, can I rely on the results being accurate, or does PostgreSQL's optimizer work more globally than that?
(Query itself omitted because I've run into this situation a few times, and would like general strategies rather than an answer for this specific query.)