Re: random() function documentation
=?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= writes: > Dean Rasheed writes: >> I think it'd be sufficient to just say that it's a deterministic >> pseudorandom number generator. I don't see much value in documenting >> the internal algorithm used. > WFM on both points. Sold then, I'll make it so. regards, tom lane
Re: random() function documentation
Dean Rasheed writes: > On Mon, 11 Apr 2022 at 20:20, Tom Lane wrote: >> >> >> How about we just say "uses a linear-feedback shift register algorithm"? > > I think it'd be sufficient to just say that it's a deterministic > pseudorandom number generator. I don't see much value in documenting > the internal algorithm used. > >> > Should we >> > perhaps also add a warning that the same seed is not guaranteed to >> > produce the same sequence across different (major?) versions? >> >> I wouldn't bother, on the grounds that then we'd need such disclaimers >> in a whole lot of places. Others might see it differently though. > > Agreed, though I think when the release notes are written, they ought > to warn that the sequence will change with this release. WFM on both points. > Regards, > Dean - ilmari
Re: random() function documentation
Fabien COELHO writes: >>> How about we just say "uses a linear-feedback shift register algorithm"? >> I think it'd be sufficient to just say that it's a deterministic >> pseudorandom number generator. I don't see much value in documenting >> the internal algorithm used. > Hmmm… I'm not so sure. ISTM that people interested in using the random > user-facing variants (only random?) could like a pointer on the algorithm > to check for the expected quality of the produced pseudo-random stream? > See attached. I don't want to get that specific. We were not specific before and there has been no call for such detail in the docs. (Unlike closed-source software, anybody who really wants algorithmic details can find all they want to know in the source code.) It would just amount to another thing to forget to update next time someone changes the algorithm ... which is a consideration that leads me to favor Dean's phrasing. regards, tom lane
Re: random() function documentation
How about we just say "uses a linear-feedback shift register algorithm"?
I think it'd be sufficient to just say that it's a deterministic
pseudorandom number generator. I don't see much value in documenting
the internal algorithm used.
Hmmm… I'm not so sure. ISTM that people interested in using the random
user-facing variants (only random?) could like a pointer on the algorithm
to check for the expected quality of the produced pseudo-random stream?
See attached.
Should we perhaps also add a warning that the same seed is not
guaranteed to produce the same sequence across different (major?)
versions?
I wouldn't bother, on the grounds that then we'd need such disclaimers
in a whole lot of places. Others might see it differently though.
Agreed,
Agreed.
though I think when the release notes are written, they ought
to warn that the sequence will change with this release.
Yes.
--
Fabien.diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 0a5c402640..7492454592 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1832,10 +1832,11 @@ repeat('Pg', 4) PgPgPgPg
- The random() function uses a simple linear
- congruential algorithm. It is fast but not suitable for cryptographic
- applications; see the module for a more
- secure alternative.
+ The random() function uses
+ https://en.wikipedia.org/wiki/Xoroshiro128%2B;>xoroshiro128**, a
+ linear feedback shift register algorithm.
+ It is fast but not suitable for cryptographic applications;
+ see the module for a more secure alternative.
If setseed() is called, the series of results of
subsequent random() calls in the current session
can be repeated by re-issuing setseed() with the same
Re: random() function documentation
On Mon, 11 Apr 2022 at 20:20, Tom Lane wrote: > > >> How about we just say "uses a linear-feedback shift register algorithm"? I think it'd be sufficient to just say that it's a deterministic pseudorandom number generator. I don't see much value in documenting the internal algorithm used. > > Should we > > perhaps also add a warning that the same seed is not guaranteed to > > produce the same sequence across different (major?) versions? > > I wouldn't bother, on the grounds that then we'd need such disclaimers > in a whole lot of places. Others might see it differently though. Agreed, though I think when the release notes are written, they ought to warn that the sequence will change with this release. Regards, Dean
Re: random() function documentation
=?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= writes: > Tom Lane writes: >> How about we just say "uses a linear-feedback shift register algorithm"? > That works for me. Nice and simple, and not overly specific. Should we > perhaps also add a warning that the same seed is not guaranteed to > produce the same sequence across different (major?) versions? I wouldn't bother, on the grounds that then we'd need such disclaimers in a whole lot of places. Others might see it differently though. regards, tom lane
Re: random() function documentation
Tom Lane writes: > =?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= writes: >> I just noticed that the since the random() rewrite¹, the documentation's >> claim² that it "uses a simple linear congruential algorithm" is no >> longer accurate (xoroshiro128** is an xorshift variant, which is a >> linear-feedback shift register algorithm). > >> I don't have a suggestion for the exact wording, since I don't know >> whether xoroshiro128** qualifies as "simple", or to what level of >> specificity we want to document the algorithm. > > How about we just say "uses a linear-feedback shift register algorithm"? That works for me. Nice and simple, and not overly specific. Should we perhaps also add a warning that the same seed is not guaranteed to produce the same sequence across different (major?) versions? > "Simple" is in the eye of the beholder anyway. Indeed. > regards, tom lane - ilmari
Re: random() function documentation
=?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= writes: > I just noticed that the since the random() rewrite¹, the documentation's > claim² that it "uses a simple linear congruential algorithm" is no > longer accurate (xoroshiro128** is an xorshift variant, which is a > linear-feedback shift register algorithm). > I don't have a suggestion for the exact wording, since I don't know > whether xoroshiro128** qualifies as "simple", or to what level of > specificity we want to document the algorithm. How about we just say "uses a linear-feedback shift register algorithm"? "Simple" is in the eye of the beholder anyway. regards, tom lane
random() function documentation
Hi Hackers, I just noticed that the since the random() rewrite¹, the documentation's claim² that it "uses a simple linear congruential algorithm" is no longer accurate (xoroshiro128** is an xorshift variant, which is a linear-feedback shift register algorithm). I don't have a suggestion for the exact wording, since I don't know whether xoroshiro128** qualifies as "simple", or to what level of specificity we want to document the algorithm. - ilmari [1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=3804539e48e794781c6145c7f988f5d507418fa8 [2] https://www.postgresql.org/docs/devel/functions-math.html#FUNCTIONS-MATH-RANDOM-TABLE
