From: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Tatsuo Ishii <ishii(at)postgresql(dot)org>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Doubt in pgbench TPS number |
Date: | 2015-09-28 16:04:44 |
Message-ID: | alpine.DEB.2.10.1509281713520.4252@sto |
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Thread: | |
Lists: | pgsql-hackers |
Hello Tom,
> FWIW, I vote with Tatsuo-san. Such a change will break comparability of
> results
I would not classify a performance measure as a "result compatibility"
issue. What matters is the *correction* of the results.
When a bug is fixed anywhere in pg it may change performance significantly
for some tests, and I have never seen this as a relevant consideration not
to fix a problem...
> with all previous versions, which means it's not something to do
> in minor releases, even if we now believe the previous results were
> somewhat bogus. Arguing that it's "not a behavioral change" seems
> quite loony to me: for most people, the TPS numbers are the only
> interesting output of pgbench.
I think that if people are interested in tps without reconnecting on each
transaction they would not run with "-C" to trigger reconnections and then
look at the "tps without connections" for the figure they want... so I do
not think that keeping this error is worth anything.
On the other hand, and on the principle, keeping the bug looks wrong. I
cannot agree with the logic behind shipping something which is known bad,
especially to display *optimistic* performances... It looks too much like
the VW way:-)
> I think we should fix it in 9.5 and document it as an incompatible
> change.
Hmm.
> (Note: I've not read the patch, so this is not an opinion about its
> correctness.)
That is another question:-)
--
Fabien.
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