Increasing checkpoint_segments - Any bad thing might happen?

From: Yan Cheng CHEOK <yccheok(at)yahoo(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: Increasing checkpoint_segments - Any bad thing might happen?
Date: 2010-05-10 00:54:39
Message-ID: 528940.67520.qm@web65704.mail.ac4.yahoo.com
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I realize that, when I have 1 threads perform frequent read, and another 3 threads to perform frequent write. I will get the following error log *sometimes*

2010-05-07 17:16:10 MYT LOG checkpoints are occurring too frequently (22 seconds apart)
2010-05-07 17:16:10 MYT HINT Consider increasing the configuration parameter "checkpoint_segments".
2010-05-07 17:31:37 MYT LOG checkpoints are occurring too frequently (29 seconds apart)
2010-05-07 17:31:37 MYT HINT Consider increasing the configuration parameter "checkpoint_segments".

My observation is, even the above logging happen, "write" operation is success when I exam the content of database.

What happen is that, the read operation fail.

read thread is spawned after 3 write threads, and read thread will only be considered as "success", only when its read result is same as what is being written by the 3 threads. The read threads will perform retry for every 200ms, lasted for 4 seconds.

I was thinking, what is the consequent of increasing "checkpoint_segments", say, from 3 to 6. Any bad thing might happen?

Thanks and Regards
Yan Cheng CHEOK

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