| From: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Rukh Meski <rukh(dot)meski(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: pgbench throttling latency limit |
| Date: | 2014-09-11 12:36:14 |
| Message-ID: | alpine.DEB.2.10.1409111402250.32582@sto |
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| Lists: | pgsql-hackers |
Hello Heikki,
> Now that I've finished the detour and committed and backpatched the changes
> to the way latency is calculated, we can get back to this patch. It needs to
> be rebased.
Before rebasing, I think that there are a few small problems with the
modification applied to switch from an integer range to double.
(1) ISTM that the + 0.5 which remains in the PoissonRand computation comes
from the previous integer approach and is not needed here. If I'm not
mistaken the formula should be plain:
-log(uniform) * center
(2) I'm not sure of the name "center", I think that "lambda" or
"mean" would be more appropriate.
(3) I wish that the maximum implied multiplier could be explicitely
documented in the source code. From pg_rand48 source code, I think
that it is 33.27106466687737
--
Fabien.
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