set global innodb_table_locks=1;
select @@innodb_table_locks;
@@innodb_table_locks
1
drop table if exists t1;
set @@innodb_table_locks=1;
create table t1 (id integer, x integer) engine=INNODB;
insert into t1 values(0, 0);
set autocommit=0;
SELECT * from t1 where id = 0 FOR UPDATE;
id	x
0	0
set autocommit=0;
lock table t1 write;
update t1 set x=1 where id = 0;
select * from t1;
id	x
0	1
commit;
update t1 set x=2 where id = 0;
commit;
unlock tables;
select * from t1;
id	x
0	2
commit;
drop table t1;
#
# Old lock method (where LOCK TABLE was ignored by InnoDB) no longer
# works due to fix for bugs  #46272 "MySQL 5.4.4, new MDL: unnecessary
# deadlock" and bug #37346 "innodb does not detect deadlock between
# update and alter table".
#
set @@innodb_table_locks=0;
create table t1 (id integer primary key, x integer) engine=INNODB;
insert into t1 values(0, 0),(1,1),(2,2);
commit;
SELECT * from t1 where id = 0 FOR UPDATE;
id	x
0	0
# Connection 'con2'.
set autocommit=0;
set @@innodb_table_locks=0;
# The following statement should block because SQL-level lock
# is taken on t1 which will wait until concurrent transaction
# is commited.
# Sending:
lock table t1 write;;
# Connection 'con1'.
# Wait until LOCK TABLE is blocked on SQL-level lock.
# We should be able to do UPDATEs and SELECTs within transaction.
update t1 set x=1 where id = 0;
select * from t1;
id	x
0	1
1	1
2	2
# Unblock LOCK TABLE.
commit;
# Connection 'con2'.
# Reap LOCK TABLE.
unlock tables;
# Connection 'con1'.
drop table t1;