From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org, Markus Schiltknecht <markus(at)bluegap(dot)ch> |
Subject: | Re: WIP patch for latestCompletedXid method of computing snapshot xmax |
Date: | 2007-09-08 21:29:05 |
Message-ID: | 6102.1189286945@sss.pgh.pa.us |
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Lists: | pgsql-hackers pgsql-patches |
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> Hmmm. Your results are withing the margin of error for DBT2, so they
> show no real difference. What we need for this is a heavy-read
> workload, though; on a workload like DBT2 (which is mostly writes) I
> wouldn't expect lazy-XID to help much.
Lazy-XID doesn't help on a write-mostly workload, but I would have
expected to see some benefit from the latestCompletedXid patch.
The rough tests I just finished suggest that the win to look for is
improvement of the very tail of the distribution --- well beyond the
90th percentile point which is the most we can see in Markus'
printout. Can we get 95% and 99% response time percentiles?
For comparison, in my little test I got 0.828546 vs 0.873957 as the
99% percentile pgbench transaction times.
regards, tom lane
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