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outdated MyISAM state.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, 9 insertions, 0 deletions

diff --git a/sql/handler.cc b/sql/handler.cc
index 01aa7491383..81981a5dcc6 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -1372,6 +1372,15 @@ int ha_delete_table(THD *thd, enum db_type table_type, const char *path,
 /****************************************************************************
 ** General handler functions
 ****************************************************************************/
+handler *handler::clone(MEM_ROOT *mem_root)
+{
+  handler *new_handler= get_new_handler(table, mem_root, table->s->db_type);
+  if (new_handler && !new_handler->ha_open(table->s->path, table->db_stat,
+                                           HA_OPEN_IGNORE_IF_LOCKED))
+    return new_handler;
+  return NULL;
+}
+
 
 	/* Open database-handler. Try O_RDONLY if can't open as O_RDWR */
 	/* Don't wait for locks if not HA_OPEN_WAIT_IF_LOCKED is set */