Dne 2.5.2011 06:53, Adarsh Sharma napsal(a): > I am also in need of a proper documentation that explains how to set > SHMAX and SHMALL variables in Postgres. > > What things need to be taken in consideration before doing that ? > What is the value of SHMAX & SHMALL if u have 16 GB RAM for Postgres > Server ?
Well, those two values actually define kernel limits for shared memory segments (i.e. memory shared by multiple processes, in this case the postmaster proces and backends). So it's rather a question of tuning shared_buffers (because that's the shared memory segment) and then setting those two values. SHMMAX - max. size of a single shared segment (in bytes) SHMALL - total size of shared segments (in pages, page is usually 4kB) So if you decide you want 1GB shared buffers, you'll need at least this SHMMAX = 1024 * 1024 * 1024 (i.e. 1GB) SHMALL = 1024 * 256 (1GB in 4kB pages) (althouth the SHMALL should be higher, as there will be other processes that need shared memory). There's a lot of docs about this, e.g. this one (it's mostly for Oracle, but it describes the shared memory quite nicely): http://www.puschitz.com/TuningLinuxForOracle.shtml#SettingSharedMemory regards Tomas -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
