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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