Hive (Spark) SQLs not working, failing with error of table lock

We had a situation recently where-in Hive or Spark Jobs stopped working resulting in Table Lock error.

On debugging Hive Metastore logs, we found following error -

ORA-00001: unique constraint (SDL_HIVE.NOTIFICATION_LOG_EVENT_ID) violated

We figured out that its an Oracle Unique Index that was throwing exception on inserting entries into NOTIFICATION_LOG table.

Hive’s metastore database primarily tracks partition locations and compaction work for the tables. Importantly, it also tracks the changes that occur in the DB so any federation/backup Hive clusters can successfully receive the data. This particular list of changes lives in the NOTIFICATION_LOG table.
The ID column in this table are incremented using NOTIFICATION_SEQUENCE table.
Somehow, new EVENT_ID(s) which were generated had already had an entry in NOTIFICATION_LOG table. Thus, we observed this failure.

Thus, to solve above issue -

We took backup of NOTIFICATION_LOG table.
And, Truncated NOTIFICATION_LOG table.

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