BUG#27516 - divide by zero crash during optimize table

When a table status is requested by statement like SHOW TABLE
STATUS and there is another statement (e.g. DELETE) sets
number of records to 0 concurrently, we may get division by
zero error, which crashes a server.

This is fixed by using thread local variable x->records instead
of shared info->state->records when we check if it is zero and
divide by it.


myisam/mi_info.c:
  Information schema does not lock a table when it requests table
  state info. If another thread sets info->state->records to 0
  after we check if it is 0 and before we divide by it we may get
  division by zero error.
  
  Check and divide by local x->records variable instead of shared
  info->state->records.

myisam/mi_info.c

@@ -57,9 +57,9 @@ int mi_status(MI_INFO *info, register MI_ISAMINFO *x, uint flag)
 
     x->keys	 	= share->state.header.keys;
     x->check_time	= share->state.check_time;
-    x->mean_reclength	= info->state->records ?
-      (ulong) ((info->state->data_file_length-info->state->empty)/
-	       info->state->records) : (ulong) share->min_pack_length;
+    x->mean_reclength= x->records ?
+      (ulong) ((x->data_file_length - x->delete_length) / x->records) :
+      (ulong) share->min_pack_length;
   }
   if (flag & HA_STATUS_ERRKEY)
   {

mysql-test/r/bdb_notembedded.result

+set autocommit=1;
+reset master;
+create table bug16206 (a int);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+show binlog events;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+f	n	Format_desc	1	n	Server ver: VERSION, Binlog ver: 4
+f	n	Query	1	n	use `test`; create table bug16206 (a int)
+f	n	Query	1	n	use `test`; insert into bug16206 values(1)
+f	n	Query	1	n	use `test`; insert into bug16206 values(2)
+drop table bug16206;
+reset master;
+create table bug16206 (a int) engine=         bdb;
+insert into bug16206 values(0);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+insert into bug16206 values(3);
+show binlog events;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+f	n	Format_desc	1	n	Server ver: VERSION, Binlog ver: 4
+f	n	Query	1	n	use `test`; create table bug16206 (a int) engine=         bdb
+f	n	Query	1	n	use `test`; insert into bug16206 values(0)
+f	n	Query	1	n	use `test`; insert into bug16206 values(1)
+f	n	Query	1	n	use `test`; BEGIN
+f	n	Query	1	n	use `test`; insert into bug16206 values(2)
+f	n	Query	1	n	use `test`; COMMIT
+f	n	Query	1	n	use `test`; insert into bug16206 values(3)
+drop table bug16206;
+set autocommit=0;
+End of 5.0 tests

mysql-test/t/bdb_notembedded.test

+-- source include/not_embedded.inc
+-- source include/have_bdb.inc
+
+#
+# Bug #16206: Superfluous COMMIT event in binlog when updating BDB in autocommit mode
+#
+set autocommit=1;
+
+let $VERSION=`select version()`;
+
+reset master;
+create table bug16206 (a int);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+--replace_result $VERSION VERSION
+--replace_column 1 f 2 n 5 n
+show binlog events;
+drop table bug16206;
+
+reset master;
+create table bug16206 (a int) engine=         bdb;
+insert into bug16206 values(0);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+insert into bug16206 values(3);
+--replace_result $VERSION VERSION
+--replace_column 1 f 2 n 5 n
+show binlog events;
+drop table bug16206;
+
+set autocommit=0;
+
+
+--echo End of 5.0 tests