Re: Separating bgwriter and checkpointer

On Tue, Sep 20, 2011 at 10:03 AM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> On 20.09.2011 11:18, Simon Riggs wrote:
>>
>> The bgwriter avoids I/O, if it is operating correctly. This patch
>> ensures it continues to operate even during heavy checkpoints. So it
>> helps avoid extra I/O during a period of very high I/O activity.
>
> I don't see what difference it makes which process does the I/O. If a
> write() by checkpointer process blocks, any write()s by the separate
> bgwriter process at that time will block too. If the I/O is not saturated,
> and the checkpoint write()s don't block, then even without this patch, the
> bgwriter process can handle its usual bgwriter duties during checkpoint just
> fine. (And if the I/O is not saturated, it's not an I/O bound system
> anyway.)

Whatever value you assign to the bgwriter, then this patch makes sure
that happens during heavy fsyncs.

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 Simon Riggs                   http://www.2ndQuadrant.com/
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