Fix performance issue in exprTypmod(): for a COALESCE expression, it

recursed twice on its first argument, leading to exponential time spent
on a deep nest of COALESCEs ... such as a deeply nested FULL JOIN would
produce.  Per report from Matt Carter.

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 750b28acdaaccf98de3589706304b222739a3a88..a16d87e409d72dc98b7e34114f792a797ca608bf 100644 (file)
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -1425,8 +1425,12 @@ exprTypmod(Node *expr)
                                int32           typmod;
                                List       *arg;
 
+                               if (exprType((Node *) lfirst(cexpr->args)) != coalescetype)
+                                       return -1;
                                typmod = exprTypmod((Node *) lfirst(cexpr->args));
-                               foreach(arg, cexpr->args)
+                               if (typmod < 0)
+                                       return -1;      /* no point in trying harder */
+                               foreach(arg, lnext(cexpr->args))
                                {
                                        Node       *e = (Node *) lfirst(arg);