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Linux mis-reporting memory

From: Decibel! <decibel(at)decibel(dot)org>
To: pgsql-performance(at)postgresql(dot)org
Subject: Linux mis-reporting memory
Date: 2007-09-20 23:04:01
Message-ID: 20070920230400.GM95343@decibel.org (view raw or flat)
Thread:
Lists: pgsql-performance
Sorry, I know this is probably more a linux question, but I'm guessing
that others have run into this...

I'm finding this rather interesting report from top on a Debian box...

Mem:  32945280k total, 32871832k used,    73448k free,   247432k buffers
Swap:  1951888k total,    42308k used,  1909580k free, 30294300k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
12492 postgres  15   0 8469m 8.0g 8.0g S    0 25.6   3:52.03 postmaster
 7820 postgres  16   0 8474m 4.7g 4.7g S    0 15.1   1:23.72 postmaster
21863 postgres  15   0 8472m 3.9g 3.9g S    0 12.4   0:30.61 postmaster
19893 postgres  15   0 8471m 2.4g 2.4g S    0  7.6   0:07.54 postmaster
20423 postgres  17   0 8472m 1.4g 1.4g S    0  4.4   0:04.61 postmaster
26395 postgres  15   0 8474m 1.1g 1.0g S    1  3.4   0:02.12 postmaster
12985 postgres  15   0 8472m 937m 930m S    0  2.9   0:05.50 postmaster
26806 postgres  15   0 8474m 787m 779m D    4  2.4   0:01.56 postmaster

This is a machine that's been up some time and the database is 400G, so
I'm pretty confident that shared_buffers (set to 8G) should be
completely full, and that's what that top process is indicating.

So how is it that linux thinks that 30G is cached?
-- 
Decibel!, aka Jim C. Nasby, Database Architect  decibel(at)decibel(dot)org 
Give your computer some brain candy! www.distributed.net Team #1828

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Subject: Re: Linux mis-reporting memory
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Subject: query io stats and finding a slow query

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