Re: pgbench - allow to specify scale as a size
От | Fabien COELHO |
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Тема | Re: pgbench - allow to specify scale as a size |
Дата | |
Msg-id | alpine.DEB.2.20.1802171823290.20813@lancre обсуждение исходный текст |
Ответ на | Re: pgbench - allow to specify scale as a size (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
Hello Tom, >> Here is a attempt at extending --scale so that it can be given a size. > > I do not actually find this to be a good idea. It's going to be > platform-dependent, or not very accurate, or both, and thereby > contribute to confusion by making results less reproducible. I have often wanted to have such an option for testing, with criterion like "within shared_buffers", "within memory", "twice the available memory", to look for behavioral changes in some performance tests. I you want reproducible (for some definition of reproducible) and accurate, you can always use scale with a number. The report provides the actual scale used anyway, so providing the size is just a convenience for the initialization phase. I agree that it cannot be really exact. Would it be more acceptable with some clear(er)/explicit caveat? > Plus, what do we do if the backend changes table representation in > some way that invalidates Kaarel's formula altogether? Then the formula (a simple linear regression, really) should have to be updated? > More confusion would be inevitable. There is no much confusion when the "scale" is reported. As for confusion, a performance tests is influenced by dozen of parameters anyway. Now if you do not want such a feature, you can mark it as rejected, and we will keep on trying to guess or look for the formula till the end of time:-) -- Fabien.
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