Re: pgbench - add pseudo-random permutation function

Suzuki Hironobu <hironobu@interdb.jp>

From: Hironobu SUZUKI <hironobu@interdb.jp>

To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Cc: Fabien COELHO <coelho@cri.ensmp.fr>

Date: 2018-10-24T14:55:57Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

pgbench: Function to generate random permutations.
- 6b258e3d688d 14.0 landed
Add basic support for using the POPCNT and SSE4.2s LZCNT opcodes
- 711bab1e4d19 12.0 cited
Further improve code for probing the availability of ARM CRC instructions.
- a7a7387575b8 11.0 cited

Hi Fabian-san,

I reviewed 'pgbench-prp-func/pgbench-prp-func-10.patch'.


On 2018/10/24 12:55, Fabien COELHO wrote:
> 
> Hello Hironobu-san,
> 
>> In pseudorandom_perm(), `modular_multiply() + (key >> LCG_SHIFT)` may 
>> overflow if the result of modular_multiply() is large. Therefore, I've 
>> improved it.
> 
>> Also, I've simplified Step 5 in modular_multiply().
> 
> Attached is a v10, where I have:
>   - updated some comments
>   - the + cannot overflow because size is taken from a signed int
>     and the added value is small thanks to the shift.
>     I have put back the simple formula and added a comment about it.
>   - added a few test cases, and fix the associated checks
> 

I agree your discussion before.

I checked the tests you added in this patch and I confirmed that there 
is no problem.

I thinks this patch is fine.

Best regards,