On 02/12/2011 05:33 PM, Noah Misch wrote:
On Sat, Feb 12, 2011 at 03:42:17PM -0600, Kevin Grittner wrote:
In two hours of testing with a 90GB production database, the copy
patch on top of HEAD ran 0.6% faster than HEAD for pg_dumpall
(generating identical output files), but feeding that in to and
empty cluster with psql ran 8.4% faster with the patch than without!
I'm going to repeat that latter with more attention to whether
everything made it in OK. (That's not as trivial to check as the
dump phase.)
Do you see any reason that COPY FROM should be significantly
*faster* with the patch?
No. Up to, say, 0.5% wouldn't be too surprising, but 8.4% is surprising. What
is the uncertainty of that figure?
We have seen in the past that changes that might be expected to slow
things down slightly can have the opposite effect. For example, see
<http://people.planetpostgresql.org/andrew/index.php?/archives/37-Puzzling-results.html>
where Tom commented:
Yeah, IME it's not unusual for microbenchmark results to move a
percent or three in response to any code change at all, even
unrelated ones. I suppose it's from effects like critical loops
breaking across cache lines differently than before.
cheers
andrew
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