Re: pgbench - add pseudo-random permutation function

From: Hironobu SUZUKI <hironobu(at)interdb(dot)jp>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: pgbench - add pseudo-random permutation function
Date: 2018-09-18 17:15:51
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Hi Fabian-san,

I reviewed 'pgbench-prp-func/pgbench-prp-func-4.patch'.

I could apply it and did the TAP test successfully. I could not find
typo in the documentations and comments.

To make sure, I checked the new routine which contains the
__builtin_popcountll() function on Linux + gcc 7.3.1 and I confirmed
that it works well.

I thinks this patch is fine.

Best regards,

On 2018/09/16 21:05, Fabien COELHO wrote:
> Hello Hironobu-san,
> Here is a v4, based on our out-of-list discussion:
>  - the mask function is factored out
>  - the popcount builtin is used if available
>> Attached a v3, based on your fix, plus some additional changes:
>> - explicitly declare unsigned variables where appropriate, to avoid casts
>> - use smaller 24 bits primes instead of 27-29 bits
>> - add a shortcut for multiplier below 24 bits and y value below 40 bits,
>>   which should avoid the manually implemented multiplication in most
>>   practical cases (tables with over 2^40 rows are pretty rare...).
>> - change the existing shortcut to look a the number of bits instead of
>>   using 32 limits.
>> - add a test for minimal code coverage with over 40 bits sizes
>> - attempt to improve the documentation
>> - some comments were updates, hopefully for the better

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