> I don't understand, are they going years between vacuums because their > data is static? In which case the index correlation won't change. Or > is it append-only, in which case I suspect the newly appended data is > likely to have the same correlation as the old data.
Append-only. And yes, one could assume that correlation wouldn't change frequently. However, it may change more frequently than vacuums occur -- I'm not exaggerating about "years". I have several clients with large databases where they have log tables which only get vacuumed for XID wraparound, once every 2 years or so. There's also the question of how we get correlation stats for a new index/table, or one which has just been upgraded. Requiring a full DB vacuum isn't practical for those using pg_upgrade. > But is there > anything stopping us from doing some sort of ANALYZE-style sample of > the index pages as well? This would be ideal. Or even a separate command to scan the indexes only to collect correlation data. Since the indexes are 20X to 100X smaller than the tables (usually), it may be practical to full-scan them even if we can't do the same with the table. -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers