| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Parag Paul <parag(dot)paul(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Issue with the PRNG used by Postgres |
| Date: | 2024-04-10 14:43:02 |
| Message-ID: | CA+TgmoatnT0WM1nQoBFG5S462ESHrL9NZk4jg4jg6KVW6OBb-Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Apr 9, 2024 at 5:05 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> ISTM that the fix here is to not use a spinlock for whatever the contention is
> on, rather than improve the RNG.
I'm not convinced that we should try to improve the RNG, but surely we
need to put parentheses around pg_prng_double(&pg_global_prng_state) +
0.5. IIUC, the current logic is making us multiply the spin delay by a
value between 0 and 1 when what was intended was that it should be
multiplied by a value between 0.5 and 1.5.
If I'm reading this correctly, this was introduced here:
commit 59bb147353ba274e0836d06f429176d4be47452c
Author: Bruce Momjian <bruce(at)momjian(dot)us>
Date: Fri Feb 3 12:45:47 2006 +0000
Update random() usage so ranges are inclusive/exclusive as required.
--
Robert Haas
EDB: http://www.enterprisedb.com
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