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List:       postgresql-admin
Subject:    Re: [ADMIN] hanging for 30sec when checkpointing
From:       Tom Lane <tgl () sss ! pgh ! pa ! us>
Date:       2004-02-10 16:41:33
Message-ID: 15924.1076431293 () sss ! pgh ! pa ! us
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"scott.marlowe" <scott.marlowe@ihs.com> writes:
>> Unfortunately not --- at checkpoint time, the constraint goes the other
>> way.  We have to be sure all the data file updates are down to disk
>> before we write a checkpoint record to the WAL log.  So you can still
>> get screwed if the data-file drive lies about write completion.

> Hmmm.  OK.  Would the transaction size be an issue here?  I.e. would small 
> transactions likely be safer against corruption than large transactions?

Transaction size would make no difference AFAICS.  Reducing the interval
between checkpoints might make things safer in such a case.

> I ask because most of the testing I did was with pgbench running 100+ 
> simos (on a -s 100 pgbench database) and as long as the WAL drive was 
> fsyncing correctly, the database survived.

Did you try pulling the plug immediately after a CHECKPOINT command
completes?  You could test by manually issuing a CHECKPOINT while
pgbench runs, and yanking power as soon as the prompt comes back.

			regards, tom lane

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