CREATE TABLE IF NOT EXISTS `user_onlines` (
  `id` bigint(14) NOT NULL,
  `gender` tinyint(1) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `user_onlines` (`id`, `gender`) VALUES($user_id, $gender)

DELETE FROM `user_onlines` WHERE id=$user_id

mysql> SHOW ENGINE INNODB STATUS;
...
------------------------
LATEST DETECTED DEADLOCK
------------------------
2015-12-20 06:43:28 7fe014e92700
*** (1) TRANSACTION:
TRANSACTION 11805790882, ACTIVE 0 sec starting index read
mysql tables in use 1, locked 1
LOCK WAIT 2 lock struct(s), heap size 360, 1 row lock(s)
MySQL thread id 372661, OS thread handle 0x7fe00da00700, query id 4037658 127.0.0.1 root updating
DELETE FROM `user_onlines` WHERE id=14505852416379
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 32472 page no 5 n bits 320 index `PRIMARY` of table `dating`.`user_onlines` trx table locks 1 total table locks 2  trx id 11805790882 lock_mode X locks rec but not gap waiting lock hold time 0 wait time before grant 0
*** (2) TRANSACTION:
TRANSACTION 11805790875, ACTIVE 0 sec inserting
mysql tables in use 1, locked 1
3 lock struct(s), heap size 1184, 2 row lock(s)
MySQL thread id 372662, OS thread handle 0x7fe014e92700, query id 4037646 127.0.0.1 root update
INSERT INTO `user_onlines` (`id`, `gender`) VALUES(14505852416379, 1)
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 32472 page no 5 n bits 320 index `PRIMARY` of table `dating`.`user_onlines` trx table locks 1 total table locks 2  trx id 11805790875 lock mode S locks rec but not gap lock hold time 0 wait time before grant 0
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 32472 page no 5 n bits 320 index `PRIMARY` of table `dating`.`user_onlines` trx table locks 1 total table locks 2  trx id 11805790875 lock_mode X locks rec but not gap waiting lock hold time 0 wait time before grant 0
*** WE ROLL BACK TRANSACTION (1)