Re: A performance issue with Memoize

Apologies for not having noticed this thread before.  I'm taking
a look at it now.  However, while sniffing around this I found
what seems like an oversight in paramassign.c's
assign_param_for_var(): it says it should compare all the same
fields as _equalVar except for varlevelsup, but it's failing to
compare varnullingrels.  Is that a bug?  It's conceivable that
it's not possible to get here with varnullingrels different and
all else the same, but I don't feel good about that proposition.

I tried adding

@@ -91,7 +91,10 @@ assign_param_for_var(PlannerInfo *root, Var *var)
                 pvar->vartype == var->vartype &&
                 pvar->vartypmod == var->vartypmod &&
                 pvar->varcollid == var->varcollid)
+            {
+                Assert(bms_equal(pvar->varnullingrels, var->varnullingrels));
                 return pitem->paramId;
+            }
         }
     }