Re: Load Distributed Checkpoints, final patch

Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Heikki Linnakangas wrote:
>> For comparison, imola-328 has full_page_writes=off. Checkpoints last ~9
>> minutes there, and the graphs look very smooth. That suggests that
>> spreading the writes over a longer time wouldn't make a difference, but
>> smoothing the rush at the beginning of checkpoint might. I'm going to
>> try the algorithm I posted, that uses the WAL consumption rate from
>> previous checkpoint interval in the calculations.

> One thing that concerns me is that checkpoint smoothing happening just
> after the checkpoint is causing I/O at the same time that
> full_page_writes is causing additional I/O.

I'm tempted to just apply some sort of nonlinear correction to the
WAL-based progress measurement. Squaring it would be cheap but is
probably too extreme. Carrying over info from the previous cycle
doesn't seem like it would help much; rather, the point is exactly
that we *don't* want a constant write speed during the checkpoint.

regards, tom lane