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Re: transaction delays to apply

From: Nickolay <nitro(at)zhukcity(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: transaction delays to apply
Date: 2009-08-13 11:54:47
Message-ID: 4A83FF07.9030805@zhukcity.ru (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane wrote:
> Nickolay <nitro(at)zhukcity(dot)ru> writes:
>   
>> BUT it seems that rarely this transaction is being delayed to apply and 
>> log entry is being inserted in wrong order:
>> ID   timestamp
>> 1     2009-08-08 00:00:00.111
>> 2     2009-08-08 00:00:30.311
>> 3     2009-08-08 00:00:00.211
>> Yep, that's right - sometimes for 30 seconds or even more.
>>     
>
> You haven't provided enough information to let anyone guess at the
> problem.  Have you checked to see if one of the processes is blocking
> on a lock, or perhaps there's a sudden spike in system load, or what?
> Watching pg_stat_activity, pg_locks, and/or "vmstat 1" output during
> one of these events might help narrow down what's happening.
>
> 			regards, tom lane
>
>   

The problem is that such thing happens very rare, and NOT at full load. 
I can't monitor the system all the time. Is there any way to investigate 
the situation by any of pgsql logs or enable something like full debug? 
I do have a row-level lock (SELECT...FOR UPDATE) on another table during 
this transaction, but one row are handled by not more than 2 processes 
at once and it should be very quick (SELECT, parse data and UPDATE).
Thank you very much for you help!

Best regards, Nick.

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