Thanks all! These point me in much better directions! Jim Nasby's approach to selecting an expression addressed some things (SELECT f.useraccount_id_b IS NOT NULL AS in_friends) Ladislav Lenart's usage of the CTE is also of a different format that I've used in the past. I think i'll be able to patch together some performance improvements now, that will last until the database structure changes. On Apr 29, 2015, at 6:54 AM, Ladislav Lenart wrote: > I think you can propagate ORDER BY and LIMIT also to the subqueries of the > UNION, i.e.: It behaves a lot better, but doesn't give me the resultset I need. Older data from one subquery is favored to newer data from another I use a similar approach on another part of this application -- where the effect on the resultset isn't as pronounced. On that query there are over 100 million total stream events. Not using an inner limit runs the query in 7 minutes; limiting the inner subquery to 1MM runs in 70 seconds... and limiting to 10k is around 100ms. On Apr 29, 2015, at 10:16 AM, Melvin Davidson wrote: > I see others have responded with suggestions to improve query performance, > but one thing I noticed when you gave the data structure is there are no > no primary keys defined for friends or posting, neither are there any indexes. > Was that an omission? This was a quick functional example to illustrate. The real tables are slightly different but do have pkeys ( 'id' is a bigserial, relationship tables (friends, memberships) use a composite key ). They are aggressively indexed and reindexed on various columns for query performance. sometimes we create an extra index that has multiple columns or partial-columns to make make scans index-only. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
