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 ec323260c55906ae434d9996355736d3b90f5303..41f605866208d27f078c9abaef53777ee10bbccb 100644 (file)
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -18,6 +18,7 @@
 #include "catalog/pg_operator.h"
 #include "catalog/pg_proc.h"
 #include "commands/dbcommands.h"
+#include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/params.h"
@@ -34,7 +35,6 @@
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
-
 bool           Transform_null_equals = false;
 
 static Node *transformColumnRef(ParseState *pstate, ColumnRef *cref);
@@ -1491,7 +1491,14 @@ exprTypmod(Node *expr)
                                {
                                        case BPCHAROID:
                                                if (!con->constisnull)
-                                                       return VARSIZE(DatumGetPointer(con->constvalue));
+                                               {
+                                                       int32 len = VARSIZE(DatumGetPointer(con->constvalue)) - VARHDRSZ;
+
+                                                       if (pg_database_encoding_max_length() > 1)
+                                                               len = pg_mbstrlen_with_len(VARDATA(DatumGetPointer(con->constvalue)), len);
+
+                                                       return len + VARHDRSZ;
+                                               }
                                                break;
                                        default:
                                                break;
@@ -1555,8 +1562,12 @@ exprTypmod(Node *expr)
                                int32           typmod;
                                ListCell   *arg;
 
+                               if (exprType((Node *) linitial(cexpr->args)) != coalescetype)
+                                       return -1;
                                typmod = exprTypmod((Node *) linitial(cexpr->args));
-                               foreach(arg, cexpr->args)
+                               if (typmod < 0)
+                                       return -1;      /* no point in trying harder */
+                               for_each_cell(arg, lnext(list_head(cexpr->args)))
                                {
                                        Node       *e = (Node *) lfirst(arg);