Re: PCTFree Results

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