On Sat, 2009-02-07 at 01:52 +0100, Thomas Finneid wrote: > Hi > > I am having some problem understanding the details of a couple of > configuration directives. Here is what I think I understand it so far: > > effective_cache_size > - specifies in how many B/KB/MB will be used to cache data > between pg and the OS? > - what is actually cached and how it is actually used by the > planner and how does it affect the planner and the queries? > -in other words, when and why do I need to set this parameter? This is just a hint to tell the planner how much cache will generally be available. The number should be reflective of your shared buffers + available operating system cache. If you database is postgresql only you can generally set this very high 75% of available ram. If not then you need to tone it down. > > checkpoint_segments > - specifies the number of segments? The number of segments that will be used before a checkpoint is forced. > size: number*16MB? Yes but they are not preallocated. > - means when number of WAL segments has filled up and matches > checkpoint segment, dirty data is written to disk? A checkpoint occurs. Joshua D. Drake -- PostgreSQL - XMPP: jdrake@xxxxxxxxxxxxxxxxxxxxx Consulting, Development, Support, Training 503-667-4564 - http://www.commandprompt.com/ The PostgreSQL Company, serving since 1997 -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
