Doc: clarify enable_indexscan=off also disabled Index Only Scans

Disabling enable_indexscan has always also disabled Index Only Scans.
Here we make that more clear in the documentation in an attempt to
prevent future complaints complaining about this expected behavior.

Reported-by: Melanie Plageman
Author: David G. Johnston, David Rowley
Backpatch-through: 12, oldest supported version
Discussion: https://postgr.es/m/CAAKRu_atV=kovgpaLREyG68PB5+ncKvJ2UNoeRetEgyC3Yb5Sw@mail.gmail.com

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 11bb573842ebad493ed7e5ea4f9044fee6c6195f..c2318844ca8f9558c46c93f4f6df4ab98e0249cd 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4995,8 +4995,9 @@ ANY num_sync ( 
       
       
        
-        Enables or disables the query planner's use of index-scan plan
-        types. The default is on.
+        Enables or disables the query planner's use of index-scan and
+        index-only-scan plan types.  The default is on.
+        Also see .
        
       
      
@@ -5011,7 +5012,9 @@ ANY num_sync ( 
        
         Enables or disables the query planner's use of index-only-scan plan
         types (see ).
-        The default is on.
+        The default is on.  The
+         setting must also be
+        enabled to have the query planner consider index-only-scans.