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Re: Extra XLOG in Checkpoint for StandbySnapshot

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Amit Kapila <amit(dot)kapila(at)huawei(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Extra XLOG in Checkpoint for StandbySnapshot
Date: 2013-01-07 13:00:03
Message-ID: CA+U5nMJLn1S72bC+B6B7fNV0a5=g+Cjj0g5AOCjnGoCBBBgLAA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 7 January 2013 12:39, Amit Kapila <amit(dot)kapila(at)huawei(dot)com> wrote:

> So We can modify to change this in function LogStandbySnapshot as below:
>                 running = GetRunningTransactionData();
>                 if (running->xcnt > 0)
>                         LogCurrentRunningXacts(running);
>
> So this check will make sure that if there is no operation happening i.e. no
> new running transaction, then no need to log running transaction snapshot
> and hence further checkpoint operations will be skipped.
>
> Let me know if I am missing something?

It's not the same test. The fact that nothing is running at that
moment is not the same thing as saying nothing at all has run since
last checkpoint.

If we skip the WAL record in the way you suggest, we'd be unable to
start quickly in some cases.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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Subject: Re: Extra XLOG in Checkpoint for StandbySnapshot
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