bzr commit into mysql-5.1-bugteam branch (joro:2905) Bug#36259

[Georgi Kodinov]

#At file:///home/kgeorge/mysql/work/B36259-5.1-bugteam/ based on revid:gshchepa@stripped

 2905 Georgi Kodinov	2009-05-28
      Bug #36259 : proof-of-concept fix (not final!).
      
      Don't accept unconditionally (without comparing the cost) 
      clustered ordering indexes.

    modified:
      sql/sql_select.cc
=== modified file 'sql/sql_select.cc'
--- a/sql/sql_select.cc	2009-05-15 13:25:29 +0000
+++ b/sql/sql_select.cc	2009-05-28 12:08:19 +0000
@@ -13124,9 +13124,9 @@ test_if_skip_sort_order(JOIN_TAB *tab,OR
       if (keys.is_set(nr) &&
           (direction= test_if_order_by_key(order, table, nr, &used_key_parts)))
       {
-        bool is_covering= table->covering_keys.is_set(nr) ||
-                          nr == table->s->primary_key &&
-	                  table->file->primary_key_is_clustered();
+        bool is_clustered= nr == table->s->primary_key &&
+                                 table->file->primary_key_is_clustered();
+        bool is_covering= table->covering_keys.is_set(nr) || is_clustered;
 	
         /* 
           Don't use an index scan with ORDER BY without limit.
@@ -13203,7 +13203,7 @@ test_if_skip_sort_order(JOIN_TAB *tab,OR
 	  */
           index_scan_time= select_limit/rec_per_key *
 	                   min(rec_per_key, table->file->scan_time());
-          if (is_covering || 
+          if ((is_covering && !is_clustered) ||
               ref_key < 0 && (group || table->force_index) ||
               index_scan_time < read_time)
           {


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