BUG#20256 - LOCK WRITE - MyISAM

Only MyISAM tables locked with LOCK TABLES ... WRITE were affected.

A query that is optimized with index_merge doesn't reflect rows
inserted within LOCK TABLES.

MyISAM doesn't flush a state within LOCK TABLES. index_merge
optimization creates a copy of the handler, which thus gets
outdated MyISAM state.

New handler->clone() method is introduced to fix this problem.
For non-MyISAM storage engines it allocates a handler and opens
it with ha_open(). For MyISAM it additionally copies MyISAM state
pointer to cloned handler.


mysql-test/r/index_merge.result:
  A test case for bug#20256.
mysql-test/t/index_merge.test:
  A test case for bug#20256.
sql/ha_myisam.cc:
  clone method added to handler class.
sql/ha_myisam.h:
  clone method added to handler class.
sql/handler.cc:
  clone method added to handler class.
sql/handler.h:
  clone method added to handler class.
sql/opt_range.cc:
  Use handler clone method.

1 files changed, 1 insertions, 4 deletions

diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index 3b77d1b419e..5866fe731cf 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -1033,10 +1033,7 @@ int QUICK_RANGE_SELECT::init_ror_merged_scan(bool reuse_handler)
   }
 
   THD *thd= current_thd;
-  if (!(file= get_new_handler(head, thd->mem_root, head->s->db_type)))
-    goto failure;
-  DBUG_PRINT("info", ("Allocated new handler %p", file));
-  if (file->ha_open(head->s->path, head->db_stat, HA_OPEN_IGNORE_IF_LOCKED))
+  if (!(file= head->file->clone(thd->mem_root)))
   {
     /* Caller will free the memory */
     goto failure;