BUG#29957 - alter_table.test fails

INSERT/DELETE/UPDATE followed by ALTER TABLE within LOCK TABLES
may cause table corruption on Windows.

That happens because ALTER TABLE writes outdated shared state
info into index file.

Fixed by removing obsolete workaround.

Affects MyISAM tables on Windows only.


myisam/mi_extra.c:
  On windows when mi_extra(HA_EXTRA_PREPARE_FOR_DELETE) is called,
  we release external lock and close index file. If we're in LOCK
  TABLES, MyISAM state info doesn't get updated until UNLOCK TABLES.
  
  That means when we release external lock and we're in LOCK TABLES,
  we may write outdated state info.
  
  As SQL layer closes all table instances, we do not need this
  workaround anymore.
mysql-test/r/alter_table.result:
  A test case for BUG#29957.
mysql-test/t/alter_table.test:
  A test case for BUG#29957.

myisam/mi_extra.c

@@ -278,7 +278,7 @@ int mi_extra(MI_INFO *info, enum ha_extra_function function, void *extra_arg)
   case HA_EXTRA_PREPARE_FOR_DELETE:
     pthread_mutex_lock(&THR_LOCK_myisam);
     share->last_version= 0L;			/* Impossible version */
-#ifdef __WIN__
+#ifdef __WIN__REMOVE_OBSOLETE_WORKAROUND
     /* Close the isam and data files as Win32 can't drop an open table */
     pthread_mutex_lock(&share->intern_lock);
     if (flush_key_blocks(share->key_cache, share->kfile,

mysql-test/r/alter_table.result

@@ -903,3 +903,15 @@ f1	f2	f21	f4	f41
 1	2000-01-01 00:00:00	2000-01-01	2002-02-02 00:00:00	2002-02-02
 drop table t1;
 set sql_mode= @orig_sql_mode;
+create table t1 (c char(10) default "Two");
+lock table t1 write;
+insert into t1 values ();
+alter table t1 modify c char(10) default "Three";
+unlock tables;
+select * from t1;
+c
+Two
+check table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+drop table t1;

mysql-test/t/alter_table.test

@@ -684,3 +684,15 @@ alter table t1 add column f4 datetime not null default '2002-02-02',
 select * from t1;
 drop table t1;
 set sql_mode= @orig_sql_mode;
+
+#
+# BUG#29957 - alter_table.test fails
+#
+create table t1 (c char(10) default "Two");
+lock table t1 write;
+insert into t1 values ();
+alter table t1 modify c char(10) default "Three";
+unlock tables;
+select * from t1;
+check table t1;
+drop table t1;