Doc: improve documentation about random().

tglsfdc · tglsfdc · commit 4c9e5162f56d · 2022-07-23T19:00:30.000-04:00
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 4203842, 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
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
@@ -1889,6 +1889,9 @@ 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>
diff --git a/doc/src/sgml/ref/set.sgml b/doc/src/sgml/ref/set.sgml
@@ -175,8 +175,7 @@ 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>
