Andres, > all visible is only set in vacuum and it determines which parts of a > table will be scanned in a non full table vacuum. So, since we won't > regularly start vacuum in the insert only case there will still be a > batch of work at once. But nearly all of that work is *already* > performed. We would just what the details of that around for a > bit. *But* since we now would only need to vacuum the non all-visible > part that would get noticeably cheaper as well.
Yeah, I can see that. Seems worthwhile, then. > I think for that case we should run vacuum more regularly for insert > only tables since we currently don't do regularly enough which a) increases > the amount of work needed at once and b) prevents index only scans from > working there. Yes. I'm not sure how we would set this though; I think it's another example of how autovacuum's parameters for when to vaccuum etc. are too simple-minded for the real world. Doing an all-visible scan on an insert-only table, for example, should be based on XID age and not on % inserted, no? Speaking of which, I need to get on revamping the math for autoanalyze. Mind you, in the real-world insert-only table case, this does create extra IO -- real insert-only tables often have a few rows ( < 5% ) which are updated/deleted. Vacuum would see these and want to clean the pages up, which would create much more substantial IO. It might still be a good tradeoff, but we should be aware of it. Unless we want a special VACUUM ALL VISIBLE mode. I vote no, unless we demonstrate some really convincing case for it. -- Josh Berkus PostgreSQL Experts Inc. http://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
