Avoid coercing a whole-row variable that is already coerced.

Marginal efficiency and beautification hack.  I'm not sure whether
this case ever arises currently, but the pending patch for update
tuple routing will cause it to arise.

Amit Khandekar

Discussion: http://postgr.es/m/CAJ3gD9cazfppe7-wwUbabPcQ4_0SubkiPFD1+0r5_DkVNWo5yg@mail.gmail.com

diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
index c5773efd19296d2562beb17dd8c18a1ff14e9739..9290c7f793600b621b929b5ea0462ca053053d56 100644 (file)
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -1224,6 +1224,7 @@ typedef struct
    /* Target type when converting whole-row vars */
    Oid         to_rowtype;
    bool       *found_whole_row;    /* output flag */
+   bool        coerced_var;    /* var is under ConvertRowTypeExpr */
 } map_variable_attnos_context;
 
 static Node *
@@ -1267,22 +1268,29 @@ map_variable_attnos_mutator(Node *node,
                    /* Don't convert unless necessary. */
                    if (context->to_rowtype != var->vartype)
                    {
-                       ConvertRowtypeExpr *r;
-
                        /* Var itself is converted to the requested type. */
                        newvar->vartype = context->to_rowtype;
 
                        /*
-                        * And a conversion node on top to convert back to the
-                        * original type.
+                        * If this var is already under a ConvertRowtypeExpr,
+                        * we don't have to add another one.
                         */
-                       r = makeNode(ConvertRowtypeExpr);
-                       r->arg = (Expr *) newvar;
-                       r->resulttype = var->vartype;
-                       r->convertformat = COERCE_IMPLICIT_CAST;
-                       r->location = -1;
-
-                       return (Node *) r;
+                       if (!context->coerced_var)
+                       {
+                           ConvertRowtypeExpr *r;
+
+                           /*
+                            * And a conversion node on top to convert back to
+                            * the original type.
+                            */
+                           r = makeNode(ConvertRowtypeExpr);
+                           r->arg = (Expr *) newvar;
+                           r->resulttype = var->vartype;
+                           r->convertformat = COERCE_IMPLICIT_CAST;
+                           r->location = -1;
+
+                           return (Node *) r;
+                       }
                    }
                }
            }
@@ -1290,6 +1298,28 @@ map_variable_attnos_mutator(Node *node,
        }
        /* otherwise fall through to copy the var normally */
    }
+   else if (IsA(node, ConvertRowtypeExpr))
+   {
+       ConvertRowtypeExpr *r = (ConvertRowtypeExpr *) node;
+
+       /*
+        * If this is coercing a var (which is typical), convert only the var,
+        * as against adding another ConvertRowtypeExpr over it.
+        */
+       if (IsA(r->arg, Var))
+       {
+           ConvertRowtypeExpr *newnode;
+
+           newnode = (ConvertRowtypeExpr *) palloc(sizeof(ConvertRowtypeExpr));
+           *newnode = *r;
+           context->coerced_var = true;
+           newnode->arg = (Expr *) map_variable_attnos_mutator((Node *) r->arg, context);
+           context->coerced_var = false;
+
+           return (Node *) newnode;
+       }
+       /* Else fall through the expression tree mutator */
+   }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
@@ -1321,6 +1351,7 @@ map_variable_attnos(Node *node,
    context.map_length = map_length;
    context.to_rowtype = to_rowtype;
    context.found_whole_row = found_whole_row;
+   context.coerced_var = false;
 
    *found_whole_row = false;