On Thu, Nov 26, 2009 at 4:20 PM, Richard Neill <rn...@cam.ac.uk> wrote:
> Dear All, > > I'm wondering whether Vacuum/analyse (notably by the autovaccuum daemon) is > responsible for some deadlocks/dropouts I'm seeing. > > One particular table gets hit about 5 times a second (for single row > updates and inserts) + associated index changes. This is a very light load > for the hardware; we have 7 CPU cores idling, and very little disk activity. > The query normally runs in about 20 ms. > > However, the query must always respond within 200ms, or userspace gets > nasty errors. [we're routing books on a sorter machine, and the book misses > its exit opportunity]. Although this is a low load, it's a bit like a > heartbeat. > > The question is, could the autovacuum daemon (running either in vacuum or > in analyse mode) be taking out locks on this table that sometimes cause the > query response time to go way up (exceeding 10 seconds)? > > I think I've set up autovacuum to do "little and often", using > autovacuum_vacuum_cost_delay = 20ms > autovacuum_vacuum_cost_limit = 20 > those are basically thresholds. So in essence you are forcing your autovacuum to be active pretty often, And from what I can read here, you are looking for completely opposite behaviour. Unless you think statistical image of your table will be completely invalid, after 20 modifications to it, which I am sure is not true. -- GJ
