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: 2018-10-23T10:11:32Z

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-9.patch (text/plain) patch

Hello,

 > Also, the alternate implementation should not change the result, so
 > something looks amiss in your version. Moreover, I'm unclear how to
 > implement an overflow multiply with the safe no overflow version.
(snip)

I made an honest mistake. I had assumed the modulo number of Knuth's LCG 
is (2 ^ 64 - 1).


BTW, I found other overflow issue.
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().


I attached pgbench-prp-func-9.patch.

Best regards,