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From: Balkrishna Sharma <b_ki@hotmail.com>
To: <pgsql-admin@postgresql.org>
Subject: Relation between RAM / shmmax / shmall / shared_buffers
Date: Tue, 25 May 2010 14:05:11 -0400
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Hi=2C
I am having a transactional database heavy on parallel reads and updates. A=
part from hardware optimization=2C I want to ensure that my system paramete=
rs are optimized as well. Following is what I am doing on my test system ha=
ving 4GB RAM. Please let me know if the logic sounds ok (at least at high-l=
evel) and if there are other related parameters I should tweak as well:
RAM =3D 4GB1. Keeping the kernel parameter kernel.shmmax at 75% of RAM (i.e=
. at 3GB )kernel.shmmax =3D 32212254722. Keeping the kernel parameter shmal=
l at the same value. Because shmall is measured in number of pages and each=
 page on my linux is 4096 bytes=2C having kernel.shmall =3D 786432     (786=
432 * 4096 =3D 3221225472=2C same as shmmax)3. Keeping the shared_buffer pa=
rameter in the postgresql.conf file to be 25% of the kernel.shmmax. i.e. sh=
ared_buffers =3D 768MB (25% of 3072 MB)

Thanks=2C-Bala
 		 	   		 =20
_________________________________________________________________
The New Busy is not the old busy. Search=2C chat and e-mail from your inbox=
.
http://www.windowslive.com/campaign/thenewbusy?ocid=3DPID28326::T:WLMTAGL:O=
N:WL:en-US:WM_HMP:042010_3=

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<html>
<head>
<style><!--
.hmmessage P
{
margin:0px=3B
padding:0px
}
body.hmmessage
{
font-size: 10pt=3B
font-family:Verdana
}
--></style>
</head>
<body class=3D'hmmessage'>
<div>Hi=2C</div><div><br></div><div>I am having a transactional database he=
avy on parallel reads and updates. Apart from hardware optimization=2C I wa=
nt to ensure that my system parameters are optimized as well. Following is =
what I am doing on my test system having 4GB RAM. Please let me know if the=
 logic sounds ok (at least at high-level) and if there are other related pa=
rameters I should tweak as well:</div><div><br></div><div>RAM =3D 4GB</div>=
<div>1. Keeping the kernel parameter kernel.shmmax at 75% of RAM (i.e. at 3=
GB )kernel.shmmax =3D 3221225472</div><div>2. Keeping the kernel parameter =
shmall at the same value. Because shmall is measured in number of pages and=
 each page on my linux is 4096 bytes=2C having kernel.shmall =3D 786432 &nb=
sp=3B &nbsp=3B (786432 * 4096 =3D 3221225472=2C same as shmmax)</div><div>3=
. Keeping the shared_buffer parameter in the postgresql.conf file to be 25%=
 of the kernel.shmmax. i.e. shared_buffers =3D 768MB (25% of 3072 MB)</div>=
<div><br></div><div><br></div><div>Thanks=2C</div><div>-Bala</div><div><br>=
</div> 		 	   		  <br /><hr />The New Busy is not the old busy. Search=2C c=
hat and e-mail from your inbox. <a href=3D'http://www.windowslive.com/campa=
ign/thenewbusy?ocid=3DPID28326::T:WLMTAGL:ON:WL:en-US:WM_HMP:042010_3' targ=
et=3D'_new'>Get started.</a></body>
</html>=

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