Robert Haas <robertmh...@gmail.com> writes:
> 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.
No, I think you are misreading it, because the assignment is += not =.
The present coding is
/* increase delay by a random fraction between 1X and 2X */
status->cur_delay += (int) (status->cur_delay *
pg_prng_double(&pg_global_prng_state) +
0.5);
which looks fine to me. The +0.5 is so that the conversion to integer
rounds rather than truncating.
In any case, I concur with Andres: if this behavior is anywhere near
critical then the right fix is to not be using spinlocks.
regards, tom lane
