Just tried to update my test cluster to 4.2.6.2 :

[ INFO  ] Stage: Misc configuration
[ INFO  ] Running vacuum full on the engine schema
[ INFO  ] Running vacuum full elapsed 0:00:04.523561
[ INFO  ] Upgrading CA
[ INFO  ] Backing up database localhost:ovirt_engine_history to '/var/lib/ovirt-engine-dwh/backups/dwh-20180814071815.xVSlda.dump'.
[ INFO  ] Creating/refreshing DWH database schema
[ INFO  ] Configuring Image I/O Proxy
[ INFO  ] Configuring WebSocket Proxy
[ INFO  ] Backing up database localhost:engine to '/var/lib/ovirt-engine/backups/engine-20180814071825.af3Hq2.dump'.
[ INFO  ] Creating/refreshing Engine database schema
[ ERROR ] schema.sh: FATAL: Cannot execute sql command: --file=/usr/share/ovirt-engine/dbscripts/upgrade/04_02_1220_default_all_search_engine_string_fields_to_not_null.sql
[ ERROR ] Failed to execute stage 'Misc configuration': Engine schema refresh failed
[ INFO  ] Yum Performing yum transaction rollback
May or may not be relevant in this case but /tmp and /var/tmp are mounted noexec.

Any more logs you need let me know.

Regards,

Brett