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Re: Write workload is causing severe slowdown in Production

From: "Gnanakumar" <gnanam(at)zoniac(dot)com>
To: "'Tomas Vondra'" <tv(at)fuzzy(dot)cz>, "'Vitalii Tymchyshyn'" <tivv00(at)gmail(dot)com>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Write workload is causing severe slowdown in Production
Date: 2012-03-22 10:32:00
Message-ID: 008e01cd0817$06418680$12c49380$@com (view raw or flat)
Thread:
Lists: pgsql-performance
> There's a checkpoint_warning option. Set it to 3600 and you should get
> messages in the log. Correlate those to the issues (do they happen at the
> same time?).
After setting "checkpoint_warning" to 3600, can you explain on how do I correlate with the messages?

> If you can, install iotop and watch the processes that cause the I/O.
I tried installing "iotop", but it failed to run because it requires Linux >= 2.6.20.  Our CentOS5.2 is 2.6.18-8.

> What we need is more details about your setup, especially
>   - checkpoint_segments
>   - checkpoint_timeout
>   - shared_buffers
# - Memory -
shared_buffers=1536MB

# - Planner Cost Constants -
effective_cache_size = 4GB

# - Checkpoints -
checkpoint_segments=32
checkpoint_timeout=5min
checkpoint_warning=270s

# - Background writer -
bgwriter_delay = 200ms
bgwriter_lru_percent = 1.0
bgwriter_lru_maxpages = 5
bgwriter_all_percent = 0.333
bgwriter_all_maxpages = 5

> also it'd be nice to have samples from the vmstat/iostat and messages from
> the log.
Unfortunately, I don't have "exact" logs when the problem actually happened



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