Kim <kim@xxxxxxxxxx> writes: > We were running on 8.1.1 previous to upgrading to 8.2, and yes, we > definitely have a heafty pg_class. The inheritance model is heavily used > in our schema (the results of the group by you wanted to see are down > below). However, no significant problems were seen with vacs while we > were on 8.1. Odd, because the 8.1 code looks about the same, and it is perfectly obvious in hindsight that its runtime is about O(N^2) in the number of relations :-(. At least that'd be the case if the stats collector output were fully populated. Did you have either stats_block_level or stats_row_level turned on in 8.1? If not, maybe the reason for the change is that in 8.2, that table *will* be pretty fully populated, because now it's got a last-vacuum-time entry that gets made even if the stats are otherwise turned off. Perhaps making that non-disablable wasn't such a hot idea :-(. What I think we need to do about this is (1) fix pgstat_vacuum_tabstats to have non-O(N^2) behavior; I'm thinking of using a hash table for the OIDs instead of a linear list. Should be a pretty small change; I'll work on it today. (2) Reconsider whether last-vacuum-time should be sent to the collector unconditionally. Comments from hackers? regards, tom lane
