Bug#17326567 MYSQL SERVER FILESORT IMPLEMENTATION HAS A VERY SERIOUS BUG

The filesort implementation needs space for at least 15 records
(plus some internal overhead) in its main sort buffer.

sql/filesort.cc

 /*
-   Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -216,7 +216,10 @@ ha_rows filesort(THD *thd, TABLE *table, SORT_FIELD *sortorder, uint s_length,
     goto err;
 
   memavl= thd->variables.sortbuff_size;
-  min_sort_memory= max(MIN_SORT_MEMORY, param.sort_length*MERGEBUFF2);
+  min_sort_memory=
+    max(MIN_SORT_MEMORY,
+        ALIGN_SIZE(MERGEBUFF2 * (param.rec_length + sizeof(uchar*))));
+
   while (memavl >= min_sort_memory)
   {
     ulong old_memavl;