Le Tuesday 14 July 2009 10:15:21, vous avez écrit : > Marc Cousin wrote: > >> Your effective_cache_size is really small for the system you seem to > >> have - its the size of IO caching your os is doing and uses no resources > >> itself. And 800MB of that on a system with that amount of data seems a > >> bit unlikely ;-) > >> > >> Using `free` you can see the amount of io caching your OS is doing atm. > >> in the 'cached' column. > >> > >> That possibly might tip some plans in a direction you prefer. > >> > >> What kind of machine are you running this on? > > > > I played with this parameter too, and it didn't influence the plan. > > Anyway, the doc says it's the OS cache available for one query, > > No they don't. I'm guessing you're getting mixed up with work_mem. I'm not (from the docs) : effective_cache_size (integer) Sets the planner's assumption about the effective size of the disk cache that is available to a single query I trust you, of course, but then I think maybe this should be rephrased in the doc then, because I understand it like I said ... I always had a doubt about this sentence, and that's why I tried both 800MB and 8GB for this parameter. > > > and there may be a lot of > > > > insert queries at the same time, so I chose to be conservative with this > > value. I tried it with 8GB too, the plans were the same. > > > > The OS cache is around 8-10GB by the way. > > That's what you need to set effective_cache_size to then. Ok but that doesn't change a thing for this query (I had a doubt on this parameter and tried with both 800MB and 8GB) -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
