2014-07-18 5:13 GMT+09:00 Fabien COELHO <coe...@cri.ensmp.fr>: > > However, ISTM that it is not the purpose of pgbench documentation to be a >>> primer about what is an exponential or gaussian distribution, so the idea >>> would yet be to have a relatively compact explanation, and that the >>> interested but clueless reader would document h..self from wikipedia or a >>> text book or a friend or a math teacher (who could be a friend as >>> well:-). >>> >> >> Well, I think it's a balance. I agree that the pgbench documentation >> shouldn't try to substitute for a text book or a math teacher, but I >> also think that you shouldn't necessarily need to refer to a text book >> or a math teacher in order to figure out how to use pgbench. Saying >> "it's complicated, so we don't have to explain it" would be a cop out; >> we need to *make* it simple. And if there's no way to do that, then >> IMHO we should reject the patch in favor of some future patch that >> implements something that will be easy for users to understand. >> >> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --exponential=10 >>>>> starting vacuum...end. >>>>> transaction type: Exponential distribution TPC-B (sort of) >>>>> scaling factor: 1 >>>>> exponential threshold: 10.00000 >>>>> >>>>> decile percents: 63.2% 23.3% 8.6% 3.1% 1.2% 0.4% 0.2% 0.1% 0.0% 0.0% >>>>> highest/lowest percent of the range: 9.5% 0.0% >>>>> >>>> >>>> I don't have a clue what that means. None. >>>> >>> >>> Maybe we could add in front of the decile/percent >>> >>> "distribution of increasing account key values selected by pgbench:" >>> >> >> I still wouldn't know what that meant. And it misses the point >> anyway: if the documentation is good, this will be unnecessary. If >> the documentation is bad, a printout that tries to illustrate it by >> example is not an acceptable substitute. >> > > The decile description is quite classic when discussing statistics.
Yeah, maybe, I and Fabien-san don't believe that he doesn't know the decile percentage. However, I think more description about decile is needed. For example, when we set the number of transaction 10,000 (-t 10000), range of aid is 100,000, and --exponential is 10, decile percents is under following as you know. decile percents: 63.2% 23.3% 8.6% 3.1% 1.2% 0.4% 0.2% 0.1% 0.0% 0.0% highest/lowest percent of the range: 9.5% 0.0% They mean that, #number of access in range of aid (from decile percents): 1 to 10,000 => 6,320 times 10,001 to 20,000 => 2,330 times 20,001 to 30,000 => 860 times ... 90,001 to 10,0000 => 0 times #number of access in range of aid (from highest/lowest percent of the range): 1 to 1,000 => 950 times ... 99,001 to 10,0000 => 0 times that's all. Their information is easy to understand distribution of access probability, isn't it? Maybe I and Fabien-san have a knowledge of mathematics, so we think decile percentage is common sense. But if it isn't common sense, I agree with adding about these explanation in the documents. Best regards, -- Mitsumasa KONDO
