Re: On disable_cost

Robert Haas <robertmhaas@gmail.com> writes:
> Well, I don't really know where to go from here. I mean, I think that
> three committers (David, Heikki, yourself) have expressed some
> concerns about changing the behavior. So maybe we shouldn't. But I
> don't understand how it's reasonable to have two very similarly named
> GUCs behave (1) inconsistently with each other and (2) in a way that
> cannot be guessed from the documentation.

If the documentation isn't adequate, that's certainly an improvable
situation.  It doesn't seem hard:

-        Enables or disables the query planner's use of index-scan plan
-        types. The default is <literal>on</literal>.
+        Enables or disables the query planner's use of index-scan plan
+        types (including index-only scans).
+        The default is <literal>on</literal>.

More to the point, if we do change the longstanding meaning of this
GUC, that will *also* require documentation work IMO.

            regards, tom lane