doc: clarify the useful features of procedures

This was not clearly documented when procedures were added in PG 11.

Reported-by: Robin Abbi
Discussion: https://postgr.es/m/CAGmg_NX327KKVuJmbWZD=pGutYFxzZjX1rU+3ji8UuX=8ONn9Q@mail.gmail.com

Backpatch-through: 11

diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 8bf497b2bf9e9f2d2971a77509feac3f977bb708..04ef0a85a723f4170da68bc2626213a36c417326 100644 (file)
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -84,8 +84,11 @@
     A procedure is a database object similar to a function.  The difference is
     that a procedure does not return a value, so there is no return type
     declaration.  While a function is called as part of a query or DML
-    command, a procedure is called explicitly using
-    the  statement.
+    command, a procedure is called in isolation using
+    the  command.  If the CALL command is not
+    part of an explicit transaction, a procedure in many server-side
+    languages can commit, rollback, and begin new transactions during
+    its execution, which is not possible in functions.