Deadlock happens randomly when I add a large number of hosts.

I am able to reproduce. After mysql's deadlock, the only way to recover is to restart zabbix:
(from my co-workers, they experienced using postsql as well.)

Error in query [UPDATE items SET itemid='3003000000322279', type='0', snmp_community='', snmp_oid='', hostid='3003000000016225', name='Number of logged in users', description='Number of users who are currently logged in.', key_='system.users.num', delay='60', history='7', trends='365', status='0', value_type='3', trapper_hosts='', units='', multiplier='0', delta='0', snmpv3_securityname='', snmpv3_securitylevel='0', snmpv3_authpassphrase='', snmpv3_privpassphrase='', formula='1', logtimefmt='', valuemapid=NULL, delay_flex='', params='', ipmi_sensor='', data_type='0', authtype='0', username='', password='', publickey='', privatekey='', flags='0', filter='', port='', inventory_link='0', lifetime='0', templateid='3003000000010016' WHERE (itemid IN ('3003000000322279')) ] [Deadlock found when trying to get lock; try restarting transaction]