At some point in time, [EMAIL PROTECTED] (Tom Lane) wrote: >Jeff Boes <[EMAIL PROTECTED]> writes: >> The "Keep" and "UnUsed" numbers seem high to me, compared to other tables. Can >> anyone interpret these and tell me anything about what we could do with this >> table to make it "look" better? > >"Keep" is the number of rows that are committed dead but had to be kept >anyway, because there are open transactions old enough to still >potentially see them. The only way to reduce that is to not have old >transactions hanging 'round while you vacuum. > >UnUsed is the number of empty line-pointer slots. At 4 bytes apiece, >this would have to vastly exceed the number of live tuples before you >should worry much.
For which values of "vastly"? I have a small table (1-2k rows) which has a ratio of UnUsed:Tuples of 50-500. The table in question has a ratio of about 10 or 11:1. For some tables (not this one), we find that it significantly improves performance (of non-indexed queries) to pg_dump and reload the table periodically. I've been asked to try to quantify (from these vacuum numbers) when we can predict that a dump-and-reload would be valuable. ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
