Re: gaussian distribution pgbench
От | Fabien COELHO |
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Тема | Re: gaussian distribution pgbench |
Дата | |
Msg-id | alpine.DEB.2.10.1407160746040.14169@sto обсуждение исходный текст |
Ответ на | Re: gaussian distribution pgbench (Robert Haas <robertmhaas@gmail.com>) |
Ответы |
Re: gaussian distribution pgbench
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Список | pgsql-hackers |
Hello Robert, > Well, I think the feedback has been pretty clear, honestly. Here's > what I'm unhappy about: I can't understand what these options are > actually doing. We can try to improve the documentation, once more! 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:-). >> [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:" > Here is an example of an explanation that would make sense to me. > This is not the actual behavior of your patch, I'm quite sure, so this > is just an example of the *kind* of explanation that I think is > needed: This is more or less the approximate behavior of the patch, but for 1% of the range, not 50%. However I'm not sure that the current documentation is so bad. > The --exponential option causes pgbench to select lower-numbered > account IDs exponentially more frequently than higher-numbered account > IDs. The argument to --exponential controls the strength of the > preference for lower-numbered account IDs, with a smaller value > indicating a stronger preference. Specifically, it is the percentage > of the total number of account IDs which will receive half the total > accesses. For example, with --exponential=10, half the accesses will > be to the smallest 10 percent of the account IDs; half the remaining > accesses will be to the next-smallest 10 percent of account IDs, and > so on. --exponential=50 therefore represents a completely flat > distribution; larger values are not allowed. -- Fabien.
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