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Doc: improve documentation about random().

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We didn't explicitly say that random() uses a randomly-chosen seed
if you haven't called setseed().  Do so.

Also, remove ref/set.sgml's no-longer-accurate (and never very
relevant) statement that the seed value is multiplied by 2^31-1.

Back-patch to v12 where set.sgml's claim stopped being true.
The claim that we use a source of random bits as seed was debatable
before 4203842a1, too, so v12 seems like a good place to stop.

Per question from Carl Sopchak.

Discussion: https://postgr.es/m/f37bb937-9d99-08f0-4de7-80c91a3cfc2e@sopchak.me
This commit is contained in:
Tom Lane 2022-07-23 19:00:30 -04:00
parent 44d0e41319
commit bd6cfbf338
2 changed files with 4 additions and 2 deletions
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3
doc/src/sgml/func.sgml
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@ -1841,6 +1841,9 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
subsequent <function>random()</function> calls in the current session
can be repeated by re-issuing <function>setseed()</function> with the same
argument.
Without any prior <function>setseed()</function> call in the same
session, the first <function>random()</function> call obtains a seed
from a platform-dependent source of random bits.
</para>
<para>

3
doc/src/sgml/ref/set.sgml
View File

@ -177,8 +177,7 @@ SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="parameter">timezone</rep
<para>
Sets the internal seed for the random number generator (the
function <function>random</function>). Allowed values are
floating-point numbers between -1 and 1, which are then
multiplied by 2<superscript>31</superscript>-1.
floating-point numbers between -1 and 1 inclusive.
</para>
<para>