7678:20170315:124407.503 using configuration file: /etc/zabbix/zabbix_server.conf
  7678:20170315:124407.509 current database version (mandatory/optional): 03010047/03010047
  7678:20170315:124407.509 required mandatory version: 03020000
  7678:20170315:124407.512 [Z3005] query failed: [1005] Can't create table 'zabbix.#sql-5ac_1338fd' (errno: 121) [alter table event_recovery add constraint c_event_recovery_3 foreign key (c_eventid) references events (eventid) on delete cascade]
  7678:20170315:124407.512 database upgrade failed

MariaDB [zabbix]> show create table `event_recovery`;
+----------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table          | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
+----------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| event_recovery | CREATE TABLE `event_recovery` (
  `eventid` bigint(20) unsigned NOT NULL,
  `r_eventid` bigint(20) unsigned NOT NULL,
  `c_eventid` bigint(20) unsigned DEFAULT NULL,
  `correlationid` bigint(20) unsigned DEFAULT NULL,
  PRIMARY KEY (`eventid`),
  KEY `event_recovery_1` (`r_eventid`),
  KEY `event_recovery_2` (`c_eventid`),
  CONSTRAINT `c_event_recovery_3` FOREIGN KEY (`c_eventid`) REFERENCES `events` (`eventid`) ON DELETE CASCADE,
  CONSTRAINT `c_event_recovery_1` FOREIGN KEY (`eventid`) REFERENCES `events` (`eventid`) ON DELETE CASCADE,
  CONSTRAINT `c_event_recovery_2` FOREIGN KEY (`r_eventid`) REFERENCES `events` (`eventid`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin |
+----------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)