Re: pgbench - add pseudo-random permutation function

Fabien COELHO <coelho@cri.ensmp.fr>

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

To: Hironobu SUZUKI <hironobu@interdb.jp>

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

Date: 2018-10-24T11:55:46Z

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

Attachments

pgbench-prp-func-10.patch (text/x-diff) patch

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

-- 
Fabien.