Re: pgbench - add pseudo-random permutation function

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Hironobu SUZUKI <hironobu(at)interdb(dot)jp>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, David Steele <david(at)pgmasters(dot)net>
Subject: Re: pgbench - add pseudo-random permutation function
Date: 2019-05-23 14:45:43
Message-ID: alpine.DEB.2.21.1905231641450.28482@lancre
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Hello Hironobu-san,

Here is a v15 which is a rebase, plus a large simplification of the modmul
function if an int128 type is available, which is probably always…

Could you have a look and possibly revalidate?

> Sorry for the late reply. I reviewed this patch.
> Function nbits(), which was previously discussed, has been simplified by
> using the function pg_popcount64().
> By adding the mathematical explanation, it has been easier to understand the
> operation of this function.
> I believe that these improvements will have a positive impact on maintenance.
> The patch could be applied successfully and the tests passed without
> problems.
> So, I think the latest patch is fine.
> Best regards,
>> On 3/3/19 12:55 PM, Fabien COELHO wrote:
>>>> Indeed, the patch needs a rebase & conflit resolution. I'll do it. Later.
>>> Here is an update:
>>>   - take advantage of pg_bitutils (although I noted that the "slow"
>>>     popcount there could be speeded-up and shorten with a bitwise operator
>>>     implementation that I just removed from pgbench).
>>>   - add comments about the bijective transformations in the code.
>>> As already stated, this function makes sense for people who want to test
>>> performance with pgbench using non uniform rands. If you do not want to do
>>> that, you will probably find the function pretty useless. I can't help it.
>>> Also, non uniform rands is also a way to test pg lock contention behavior.
>> You have signed up as a reviewer for this patch.  Do you know when you'll
>> have time to do the review?
>> Regards,

Fabien Coelho - CRI, MINES ParisTech

Attachment Content-Type Size
pgbench-prp-func-15.patch text/x-diff 17.9 KB

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