Bug#20789 Merge Subtable Rename Causes Crash

 - When an ALTER TABLE RENAME is performed on windows, the files are closed and their cached file 
   descriptors are marked invalid. Performing INSERT, UPDATE or SELECT on the associated merge
   table causes a server crash on windows. This patch adds a test for bad file descriptors when a 
   table attempts a lock. If a bad descriptor is found an error is thrown. An additional FLUSH TABLES
   will be necessary to further operate on the associated merge table.

myisam/mi_locking.c

@@ -223,7 +223,18 @@ int mi_lock_database(MI_INFO *info, int lock_type)
     default:
       break;				/* Impossible */
     }
+  } 
+#ifdef __WIN__
+  else
+  {
+    /*
+      The file has been closed and kfile is -1.
+      See mi_extra.c about implementation of
+      HA_EXTRA_PREPARE_FOR_DELETE.
+    */
+    error=HA_ERR_NO_SUCH_TABLE;
   }
+#endif
   pthread_mutex_unlock(&share->intern_lock);
 #if defined(FULL_LOG) || defined(_lint)
   lock_type|=(int) (flag << 8);		/* Set bit to set if real lock */

mysql-test/r/windows.result

@@ -6,3 +6,31 @@ use prn;
 ERROR 42000: Unknown database 'prn'
 create table nu (a int);
 drop table nu;
+CREATE TABLE `t1` (
+`TIM` datetime NOT NULL,
+`VAL` double default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+CREATE TABLE `t2` (
+`TIM` datetime NOT NULL,
+`VAL` double default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+CREATE TABLE `mt` (
+`TIM` datetime NOT NULL,
+`VAL` double default NULL
+) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 INSERT_METHOD=LAST
+UNION=(`t1`,`t2`);
+INSERT INTO mt VALUES ('2006-01-01',0);
+ALTER TABLE `t2` RENAME TO `t`;
+INSERT INTO mt VALUES ('2006-01-01',0);
+ERROR HY000: Can't lock file (errno: 155)
+select * from mt;
+ERROR HY000: Can't lock file (errno: 155)
+FLUSH TABLES;
+select * from mt;
+ERROR HY000: Can't find file: 'mt' (errno: 2)
+ALTER TABLE `t` RENAME TO `t2`;
+INSERT INTO mt VALUES ('2006-01-01',0);
+select * from mt;
+TIM	VAL
+2006-01-01 00:00:00	0
+2006-01-01 00:00:00	0

mysql-test/t/windows.test

@@ -18,3 +18,42 @@ create table nu (a int);
 drop table nu;
 
 # End of 4.1 tests
+
+#
+# Bug #20789: Merge Subtable Rename Causes Crash
+#
+CREATE TABLE `t1` (
+  `TIM` datetime NOT NULL,
+  `VAL` double default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+CREATE TABLE `t2` (
+  `TIM` datetime NOT NULL,
+  `VAL` double default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+CREATE TABLE `mt` (
+  `TIM` datetime NOT NULL,
+  `VAL` double default NULL
+) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 INSERT_METHOD=LAST
+UNION=(`t1`,`t2`);
+
+# insert into the merge table and thus open it.
+INSERT INTO mt VALUES ('2006-01-01',0);
+
+# Alter one of the tables that are part of the merge table
+ALTER TABLE `t2` RENAME TO `t`;
+
+# Insert into the merge table that has just been altered
+--error 1015
+INSERT INTO mt VALUES ('2006-01-01',0); 
+--error 1015
+select * from mt;
+
+FLUSH TABLES;
+--error 1017
+select * from mt;
+
+# Alter one of the tables that are part of the merge table
+ALTER TABLE `t` RENAME TO `t2`;
+INSERT INTO mt VALUES ('2006-01-01',0);
+select * from mt; 
+