InnoDB engine doesn't honor unique key constraints, under a heavy load

[Rushin Fernando]

I have the following table in my database.

CREATE TABLE `IDN_OAUTH2_ACCESS_TOKEN` (
`ACCESS_TOKEN` varchar(255) NOT NULL DEFAULT '',
`REFRESH_TOKEN` varchar(255) DEFAULT NULL,
`CONSUMER_KEY` varchar(255) DEFAULT NULL,
`AUTHZ_USER` varchar(100) DEFAULT NULL,
`USER_TYPE` varchar(25) DEFAULT NULL,
`TIME_CREATED` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
`VALIDITY_PERIOD` bigint(20) DEFAULT NULL,
`TOKEN_SCOPE` varchar(25) DEFAULT NULL,
`TOKEN_STATE` varchar(25) DEFAULT 'ACTIVE',
`TOKEN_STATE_ID` varchar(255) DEFAULT 'NONE',
PRIMARY KEY (`ACCESS_TOKEN`),
UNIQUE KEY `APP_CON_KEY` (`CONSUMER_KEY`,`AUTHZ_USER`,`USER_TYPE`,`TOKEN_SCOPE`,`TOKEN_STATE`,`TOKEN_STATE_ID`),
KEY `IDX_AT_CK_AU` (`CONSUMER_KEY`,`AUTHZ_USER`,`TOKEN_STATE`,`USER_TYPE`),
CONSTRAINT `IDN_OAUTH2_ACCESS_TOKEN_ibfk_1` FOREIGN KEY (`CONSUMER_KEY`) REFERENCES `IDN_OAUTH_CONSUMER_APPS` (`CONSUMER_KEY`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

In my application I execute the following queries in order. (please note that the values are samples)

1)SELECT ACCESS_TOKEN, AUTHZ_USER, TOKEN_SCOPE, TOKEN_STATE FROM IDN_OAUTH2_ACCESS_TOKEN WHERE CONSUMER_KEY = 'a7ede2ff2ccf4946aa4176ff9577448d' AND REFRESH_TOKEN = '0f972d6fea304c5ea15e325941a97666' ORDER BY TIME_CREATED DESC LIMIT 1

2)INSERT INTO IDN_OAUTH2_ACCESS_TOKEN (ACCESS_TOKEN, REFRESH_TOKEN, CONSUMER_KEY, AUTHZ_USER, TIME_CREATED, VALIDITY_PERIOD, TOKEN_SCOPE, TOKEN_STATE, USER_TYPE) VALUES ('6bbcf2c04aa2fa787a639f85b13c90af','fe01784f3aa81511b25cbfa2fe2c082','a7ede2ff2ccf4946aa4176ff9577448d','primary/[e-mail]','2015-03-19 11:38:42',300000,'PRODUCTION','ACTIVE','APPLICATION_USER')

The table has around 600k entries. So that first query takes around 60 secs to complete while MySQL is consuming 400% CPU load.

If we execute these query set for 2 concurrent users while MySQL is consuming 400% CPU, I can see duplicate entries, which should be not possible since we have a foreign key constraint.

e.g.

1) 'c09eccdd662f11b736ea9c9bd983e3', '6fea8edd4d22c23883958c455092a35e', 'a7ede2ff2ccf4946aa4176ff9577448d', 'primary/[e-mail]', 'APPLICATION_USER', '2015-03-19 13:57:36', '300000', 'PRODUCTION', 'ACTIVE', 'NONE'

2) 'c09eccdd662f11b736ea9c9bd983e4', '6fea8edd4d22c23883958c455092a35c', 'a7ede2ff2ccf4946aa4176ff9577448d', 'primary/[e-mail]', 'APPLICATION_USER', '2015-03-19 13:57:36', '300000', 'PRODUCTION', 'ACTIVE', 'NONE'


Can someone please help me to figure this out?