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* Relation between RAM / shmmax / shmall / shared_buffers
@ 2010-05-25 18:05 Balkrishna Sharma <b_ki@hotmail.com>
0 siblings, 2 replies; 3+ messages in thread
From: Balkrishna Sharma @ 2010-05-25 18:05 UTC (permalink / raw)
To: pgsql-admin
Hi,
I am having a transactional database heavy on parallel reads and updates. Apart from hardware optimization, I want 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 parameters I should tweak as well:
RAM = 4GB1. Keeping the kernel parameter kernel.shmmax at 75% of RAM (i.e. at 3GB )kernel.shmmax = 32212254722. 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, having kernel.shmall = 786432 (786432 * 4096 = 3221225472, same as shmmax)3. Keeping the shared_buffer parameter in the postgresql.conf file to be 25% of the kernel.shmmax. i.e. shared_buffers = 768MB (25% of 3072 MB)
Thanks,-Bala
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^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Relation between RAM / shmmax / shmall / shared_buffers
@ 2010-05-25 18:10 Kevin Grittner <Kevin.Grittner@wicourts.gov>
parent: Balkrishna Sharma <b_ki@hotmail.com>
1 sibling, 0 replies; 3+ messages in thread
From: Kevin Grittner @ 2010-05-25 18:10 UTC (permalink / raw)
To: Balkrishna Sharma <b_ki@hotmail.com>; pgsql-admin
Balkrishna Sharma <b_ki@hotmail.com> wrote:
> [Are there] other related parameters I should tweak as well[?]
There are several which should probably be adjusted. See:
http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server
-Kevin
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Relation between RAM / shmmax / shmall / shared_buffers
@ 2010-05-28 19:08 Greg Smith <greg@2ndquadrant.com>
parent: Balkrishna Sharma <b_ki@hotmail.com>
1 sibling, 0 replies; 3+ messages in thread
From: Greg Smith @ 2010-05-28 19:08 UTC (permalink / raw)
To: Balkrishna Sharma <b_ki@hotmail.com>; +Cc: pgsql-admin
Balkrishna Sharma wrote:
> 1. Keeping the kernel parameter kernel.shmmax at 75% of RAM (i.e. at
> 3GB )kernel.shmmax = 3221225472
> 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, having kernel.shmall = 786432 (786432 * 4096 =
> 3221225472, same as shmmax)
There's little reason to put shmmax at over 50% of RAM, because
shared_buffers is going to be significantly lower than that even. I use
the attached script for this job now; I got sick of doing the math
manually all the time. If you're on a system that supports returning
memory info using getconf, it outputs the lines you need to put into the
kernel configuration.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.us
Attachments:
shmsetup (text/plain, 914B) download
#!/bin/bash
# Output lines suitable for sysctl configuration based
# on total amount of RAM on the system. The output
# will allow up to 50% of physical memory to be allocated
# into shared memory.
# On Linux, you can use it as follows (as root):
#
# ./shmsetup >> /etc/sysctl.conf
# sysctl -p
# Early FreeBSD versions do not support the sysconf interface
# used here. The exact version where this works hasn't
# been confirmed yet.
page_size=`getconf PAGE_SIZE`
phys_pages=`getconf _PHYS_PAGES`
if [ -z "$page_size" ]; then
echo Error: cannot determine page size
exit 1
fi
if [ -z "$phys_pages" ]; then
echo Error: cannot determine number of memory pages
exit 2
fi
shmall=`expr $phys_pages / 2`
shmmax=`expr $shmall \* $page_size`
echo \# Maximum shared segment size in bytes
echo kernel.shmmax = $shmmax
echo \# Maximum number of shared memory segments in pages
echo kernel.shmall = $shmall
end of thread, other threads:[~2010-05-28 19:08 UTC | newest]
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2010-05-25 18:05 Relation between RAM / shmmax / shmall / shared_buffers Balkrishna Sharma <b_ki@hotmail.com>
2010-05-25 18:10 ` Kevin Grittner <Kevin.Grittner@wicourts.gov>
2010-05-28 19:08 ` Greg Smith <greg@2ndquadrant.com>
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