Re: Checkpoint cost, looks like it is WAL/CRC

Did you test with full_page_writes on and off?

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Josh Berkus wrote:
> Tom,
>
> > This will remove just the CRC calculation work associated with backed-up
> > pages. ?Note that any attempt to recover from the WAL will fail, but I
> > assume you don't need that for the purposes of the test run.
>
> Looks like the CRC calculation work isn't the issue. I did test runs of
> no-CRC vs. regular DBT2 with different checkpoint timeouts, and didn't
> discern any statistical difference. See attached spreadsheet chart (the
> two different runs are on two different machines).
>
> I think this test run http://khack.osdl.org/stp/302903/results/0/, with a
> 30-min checkpoint shows pretty clearly that the behavior of the
> performance drop is consistent with needing to "re-prime" the WAL will
> full page images. Each checkpoint drops performance abruptly, and then
> slowly recovers until the next checkpoint.
>
> Do note that there is a significant statistical variation in individual
> runs. It's only the overall trend which is significant.
>
> --
> --Josh
>
> Josh Berkus
> Aglio Database Solutions
> San Francisco

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