> From: Huan Ruan <huan.ruan.it@xxxxxxxxx> >To: pgsql-performance@xxxxxxxxxxxxxx >Sent: Thursday, 15 January 2015, 11:30 >Subject: shared_buffers vs Linux file cache > > > >Hi All > > >I thought 'shared_buffers' sets how much memory that is dedicated to PostgreSQL to use for caching data, therefore not available to other applications. > > >However, as shown in the following screenshots, The server (CentOS 6.6 64bit) has 64GB of RAM, and 'shared_buffer' is set to 32GB, but the free+buffer+cache is 60GB. > > >Shouldn't the maximum value for free+buffer+cache be 32GB ( 64 - 32)? >Is 'shared_buffers' pre allocated to Postgres, and Postgres only? > I've not looked at the images, but I think you're getting PostgreSQL shared_buffers and the OS buffercache mixed up; they are not the same. PostgreSQL shared_buffers is specific to postgres, whereas the OS buffercache will just use free memory to cache data pages from disk, and this is what you're seeing. Some reading for you: http://www.tldp.org/LDP/sag/html/buffer-cache.html Glyn -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
