further , can pg_buffercache view serve as a guide to setting appropriate value of shared_buffers ? when i do SELECT count(*) from pg_buffercache where relfilenode is null ; to check unused buffers i find that it has been 0 most of the time. Can shared_buffers be raised to an extent that some buffers remains unused mostly. I read in one of the articles http://www.varlena.com/GeneralBits/Tidbits/perf.html#shbuf that shared_buffers can be put 1.2 to 2 times the peak shared mem usage. My question is how to roughly determine the appropriate value for shared_buffers. Also, What if most of the memory is left for kernel disk buffer cache ? is fetching from kernel disk buffer cache significantly expensive compared to getting from shared buffer cache ? regds mallah. On Thu, Feb 5, 2009 at 6:48 PM, Rajesh Kumar Mallah <mallah.rajesh@xxxxxxxxx> wrote: > Hi , > > I have following setting in my postgresql.conf file. > > shared_buffers = 10000 (8k blocks) ; which is apprx 80MB > > my question is how can i know how much is the usage > of the shared_buffers so that it can be increased or > decreased. below is the output of ipcs , I am wondering > is postgres using 420MB shared memory (but shared_buffers > is only 80MB) > > $ ipcs -m > > ------ Shared Memory Segments -------- > key shmid owner perms bytes nattch status > 0x00000000 3637248 postgres 600 52228 0 > 0x0052e6a9 7798785 postgres 600 40034304 42 > 0x00000000 4489218 postgres 600 52228 0 > 0x00000000 4521987 postgres 600 52228 0 > 0x00000000 4554756 postgres 600 52228 0 > 0x00000000 4587525 postgres 600 52228 0 > 0x00000000 4620294 postgres 600 52228 0 > 0x00000000 2883591 postgres 600 52228 0 > 0x00000000 3670024 postgres 600 74240 0 > 0x00000000 3702793 postgres 600 768 0 > 0x00000000 3735562 postgres 600 524 0 > 0x00000000 3768331 postgres 600 4 0 > 0x0052e2c1 7831564 postgres 600 420610048 121 > > regds > mallah. > -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
