server gets slow at certain time

On 29 October 2010 13:24, AI Rumman <rummandba@gmail.com> wrote:

I am using Postgresql 8.1 in 8-cpu cores with 32 gb ram with CestOS 5.
I have different DBs in the system and the large one is 12 GB and it is a
CRM DB and heavily used.
Every day after 1 pm the system gets slow and after analyzing the nmon
spreadsheet, I found that IO spike at that period.
Users write data much at that period of time.
DB parameters are as follows:
max_connections= 500
shared_buffers=122144
effective_cache_size = 1835010
work_mem = 8192
max_fsm_pages= 356656
fsync=on
commit_delay=0
commit_siblings= 5
random_page_cost = 0.01
default_statistics_target=100
wah_buffers = 500

Any idea please how to find the bottleneck and improve performance.
Let me know if any more information is needed.

What's your checkpoint_segments setting? You may wish to up it if you're
getting many inserts/updates.

--
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935

On Fri, 2010-10-29 at 18:24 +0600, AI Rumman wrote:

I am using Postgresql 8.1 in 8-cpu cores with 32 gb ram with CestOS 5.

<snip>

In addition to what Thom wrote, please note that checkpoints in pre-8.3
negative effect on disk I/O -- you may see spikes during checkpoints.
--
Devrim GÜNDÜZ
PostgreSQL Danışmanı/Consultant, Red Hat Certified Engineer
PostgreSQL RPM Repository: http://yum.pgrpms.org
Community: devrim~PostgreSQL.org, devrim.gunduz~linux.org.tr
http://www.gunduz.org Twitter: http://twitter.com/devrimgunduz

At present,
checkpoint_segment=3
checkpoint_timeout=300

On 29 October 2010 14:34, AI Rumman <rummandba@gmail.com> wrote:

At present,
checkpoint_segment=3
checkpoint_timeout=300

I'd recommend at least setting checkpoint_segments to 12 and you might want
to increase checkpoint_timeout too, although not too high. Maybe try
doubling it.

And as Devrim pointed out, pre-8.3 versions suffer from these problems more,
and 8.1 will cease to be supported in the near future, so if you're able to,
upgrade. :)

Thom