connect  prevent_purge,localhost,root,,;
START TRANSACTION WITH CONSISTENT SNAPSHOT;
connection default;
SET GLOBAL innodb_monitor_disable='lock_row_lock_time_avg';
CREATE TABLE `t` (a INT PRIMARY KEY) engine=InnoDB STATS_PERSISTENT=0;
INSERT INTO t VALUES (5);
SELECT name, count FROM information_schema.innodb_metrics
WHERE name ='lock_row_lock_current_waits';
name	count
lock_row_lock_current_waits	0
connect  con1,localhost,root,,;
BEGIN;
SELECT * FROM t FOR UPDATE;
a
5
connect  con2,localhost,root,,;
SET DEBUG_SYNC="lock_wait_before_suspend SIGNAL blocked WAIT_FOR cont";
BEGIN;
SELECT * FROM t FOR UPDATE;
connection default;
SET DEBUG_SYNC="now WAIT_FOR blocked";
SELECT name, count FROM information_schema.innodb_metrics
WHERE name ='lock_row_lock_current_waits';
name	count
lock_row_lock_current_waits	1
SET GLOBAL innodb_monitor_disable='lock_row_lock_current_waits';
SET GLOBAL innodb_monitor_reset_all='lock_row_lock_current_waits';
SET GLOBAL innodb_monitor_enable='lock_row_lock_current_waits';
SELECT name, count FROM information_schema.innodb_metrics
WHERE name ='lock_row_lock_current_waits';
name	count
lock_row_lock_current_waits	1
SET DEBUG_SYNC="now SIGNAL cont";
disconnect con1;
connection con2;
a
5
COMMIT;
disconnect con2;
connection default;
SET DEBUG_SYNC="reset";
SELECT name, count FROM information_schema.innodb_metrics
WHERE name ='lock_row_lock_current_waits';
name	count
lock_row_lock_current_waits	0
DROP TABLE `t`;
SET GLOBAL innodb_monitor_disable='lock_row_lock_current_waits';
SET GLOBAL innodb_monitor_reset_all='lock_row_lock_current_waits';
SET GLOBAL innodb_monitor_enable='lock_row_lock_current_waits';
SET GLOBAL innodb_monitor_enable='lock_row_lock_time_avg';
SET GLOBAL innodb_monitor_disable=default;
SET GLOBAL innodb_monitor_reset_all=default;
SET GLOBAL innodb_monitor_enable=default;
disconnect prevent_purge;