> -----Original Message----- > From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance- > owner@xxxxxxxxxxxxxx] On Behalf Of tv@xxxxxxxx > Sent: Wednesday, March 23, 2011 10:42 AM > To: Uwe Bartels > Cc: pgsql-performance@xxxxxxxxxxxxxx > Subject: Re: buffercache/bgwriter > > > Hi, > > > > I have very bad bgwriter statistics on a server which runs since many > > weeks > > and it is still the same after a recent restart. > > There are roughly 50% of buffers written by the backend processes and > the > > rest by checkpoints. > > The statistics below are from a server with 140GB RAM, 32GB > shared_buffers > > and a runtime of one hour. > > > > As you can see in the pg_buffercache view that there are most buffers > > without usagecount - so they are as free or even virgen as they can > be. > > At the same time I have 53% percent of the dirty buffers written by > the > > backend process. > > There are some nice old threads dealing with this - see for example > > http://postgresql.1045698.n5.nabble.com/Bgwriter-and-pg-stat-bgwriter- > buffers-clean-aspects-td2071472.html > > http://postgresql.1045698.n5.nabble.com/tuning-bgwriter-in-8-4-2- > td1926854.html > > and there even some nice external links to more detailed explanation > > http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm The interesting question here is - with 3 million unallocated buffers, why is the DB evicting buffers (buffers_backend column) instead of allocating the unallocated buffers? Brad. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
