Looking at https://community.hortonworks.com/questions/40382/hive-throws-database-already-exists-error-while-cr... suggests that HiveMetastore might not be running, but it is and we haven't received alerts to suggest it wasn't. We connect (Hive Metastore) to an external Oracle database though, wondering if network latency with this database could cause this error?
ERROR [HiveServer2-Background-Pool: Thread-102344]: metastore.RetryingHMSHandler (RetryingHMSHandler.java:invoke(159)) - AlreadyExistsException(message:Database clickstream already exists)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
To clarify, this is happening only intermittently when run though a NiFI processor. Typcially early in the morning