Gary Warner <gar@xxxxxxxxxxx> writes: > Recently my database stopped respecting one of my indexes, which took a query that should run in "subsecond response time" and turning it into something that with small data sets runs in the 7-10 minute range and with large data sets runs in the 30 minute - eternity range. > Explain Analyze tells me that what used to be an Index Scan has become a Seq Scan, doing a full table scan through 140 million records. > Any thoughts on why that happens? I'd bet it has a lot to do with the nigh-three-orders-of-magnitude overestimates of the numbers of matching rows. You might find that increasing the statistics targets for the indexed columns helps --- I'm guessing that these particular key values are out in the long tail of a highly skewed distribution, and the planner needs a larger MCV list to convince it that non-MCV values will not occur very many times. If that is an accurate guess, then trying to force the matter with something like enable_seqscan = off is not a good production solution, because it will result in horrid plans whenever you decide to query a not-so-infrequent value. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
