Tom,
> I dug through the CVS logs since 5-July (when full_page_writes was
> added, so I suppose that's before your unspecified "July" test).
> AFAICS the only changes that might possibly affect xlog/checkpoint
> performance were these:
>
> Use O_DIRECT if available when using O_SYNC for wal_sync_method.
>
> Also, write multiple WAL buffers out in one write() operation.
>
> Was your test set up so that it would have used O_DIRECT?
Yes, actually. It's Linux, and we used the defaults.
It would be interesting to test on a system that doesn't support the above
and see if full_page_writes=off still makes a significant difference.
> With respect to the original point, I'm pretty nervous about either
> accepting or rejecting a performance-oriented patch on the strength
> of a single test case. This report certainly doesn't favor the PCTFREE
> patch, but it probably shouldn't kill it either. Anyone want to try it
> on some other test cases?
Right, this doesn't kill PCTFree, what it does is fail to make a case for
it.
--
--Josh
Josh Berkus
Aglio Database Solutions
San Francisco