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outdated MyISAM state.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.

1 files changed, 1 insertions, 0 deletions

diff --git a/sql/ha_myisam.h b/sql/ha_myisam.h
index ca684463311..950817d42bd 100644
--- a/sql/ha_myisam.h
+++ b/sql/ha_myisam.h
@@ -45,6 +45,7 @@ class ha_myisam: public handler
  public:
   ha_myisam(TABLE *table_arg);
   ~ha_myisam() {}
+  handler *clone(MEM_ROOT *mem_root);
   const char *table_type() const { return "MyISAM"; }
   const char *index_type(uint key_number);
   const char **bas_ext() const;