Handing a failed verification

Although you stopped ETL jobs and set Ranger policies to prevent writes to databases, a database write still might occur. This causes a verification failure. You need to find out if such a write caused the failure.

  • You completed the replication of Hive data from HDP to CDP.
  • The last event id in the output is at least the checkpoint id for all databases, but does not match the checkpoint id.
  • You noted the HDP notification event id, which you use later as a checkpoint id.
  1. On the backend RDBMS of the HDP cluster, run a query to determine if any writes occurred during replication.
    select * from NOTIFICATION_LOG where event_id > <HDP notification event id > and event_type = 'COMMIT_TXN';
    This query gets all commit transaction (TXN) events after the HDP checkpoint event-id.
    If there are no commit events, the output looks something like this:
    If there are no commit events, assume all valid writes are replicated. Skip the rest of the steps. The migration is done.

    If there are commit events, continue to the next step.

  2. Run a query to get information about the writes.
    select event_type,db_name, count(*) from NOTIFICATION_LOG 
    where event_id > <HDP notification event id >  
    group by db_name,event_type order by db_name;
    The output might look something like this:
  3. Identify clients who wrote to the database, and stop further attempts.
    You can use Ranger audits, if enabled, to identify such clients as described in Managing Auditing.
  4. Repeat the procedure "Verifying replication".