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Re: cached memory

From: dx k9 <bitsandbytes88(at)hotmail(dot)com>
To: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Cc: posgres support <pgsql-admin(at)postgresql(dot)org>
Subject: Re: cached memory
Date: 2007-11-15 14:06:42
Message-ID: BAY116-W16C6F5A0A953E65D275AF5D1820@phx.gbl (view raw or flat)
Thread:
Lists: pgsql-admin
Hi Scott,
 
Thanks for the reply.
 
Top is showing 10157008 / 15897160 in kernel cache, so postgres is using 37% right now, following what you are saying.  I realize the load isn't peaking right now, but wouldn't it be nice to have some of the indexes cached in memory?
In your case 1868064 / 2000000 or 7 % of your memory is being used by postgres.  That sort of proves my point.  Shouldn't postgres use more than 7% of the memory.  Doesn't that seem like 93% isn't being used?  
 
~DjK
 
top - 08:59:38 up 277 days, 23:03,  1 user,  load average: 0.63, 0.51, 0.40Tasks: 101 total,   1 running, 100 sleeping,   0 stopped,   0 zombieCpu0  :  0.0% us,  1.0% sy,  0.0% ni, 99.0% id,  0.0% wa,  0.0% hi,  0.0% siCpu1  :  0.0% us,  0.0% sy,  0.0% ni, 99.7% id,  0.3% wa,  0.0% hi,  0.0% siCpu2  :  0.7% us,  0.7% sy,  0.0% ni, 98.3% id,  0.0% wa,  0.0% hi,  0.3% siCpu3  :  0.0% us,  0.0% sy,  0.0% ni, 99.3% id,  0.7% wa,  0.0% hi,  0.0% siMem:  15897160k total, 10477104k used,  5420056k free,   169780k buffersSwap: 16779768k total,    78912k used, 16700856k free, 10157008k cached
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND 1975 postgres  15   0 33412 7932 1388 S  1.0  0.0   1211:09 postgres: stats collector process 1971 postgres  15   0 1085m  14m  14m S  0.3  0.1   2323:28 /postgres    1 root      16   0   640   80   48 S  0.0  0.0   0:11.55 init [3]    2 root      RT   0     0    0    0 S  0.0  0.0   0:02.30 [migration/0]    3 root      34  19     0    0    0 S  0.0  0.0   0:06.99 [ksoftirqd/0]    4 root      RT   0     0    0    0 S  0.0  0.0   0:00.82 [migration/1]    5 root      34  19     0    0    0 S  0.0  0.0   0:56.60 [ksoftirqd/1]    6 root      RT   0     0    0    0 S  0.0  0.0   0:10.71 [migration/2]    7 root      34  19     0    0    0
 
> Date: Wed, 14 Nov 2007 15:20:53 -0600> From: scott(dot)marlowe(at)gmail(dot)com> To: bitsandbytes88(at)hotmail(dot)com> Subject: Re: [ADMIN] cached memory> CC: pgsql-admin(at)postgresql(dot)org> > On Nov 14, 2007 3:13 PM, dx k9 <bitsandbytes88(at)hotmail(dot)com> wrote:> >> > In looking at some cacti memory usage graphs, the Oracle servers show> > only 6 of a total of16 GB of RAM as 'Total Available'. Whereas, our> > Postgres version 8.24 servers show all 16 GB of RAM totally available or> > free. Some people are asking why Postgres doesn't take that memory and> > lock into it, so you can't see less 'total available' memory. We use a lot> > of B-tree indexes. This may or may not be related, but it there a good way> > to make sure those stay in memory?> > Not sure what you mean by totally available. Is the OS using it to> cache? If so, why should postgresql do what the OS already does so> well.> > Oracle was written back when OSes were barely more than program> loaders and it had to do everything, from having its own file systems> to buffering / caching to memory management to job schedulers.> > PostgreSQL was written as Unix was maturing (mostly) and takes> advantage of all the cool things a modern unix comes with, and one of> those things is kernel level caching of disk files.> > So, what does free / top have to say about your memory? And how hard> have these servers been working. For instance, my RHEL4 reporting> server, with only 2 Gigs in it shows 1868064 used as kernel cache.> The rest is mostly pgsql processes
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