For databases using mirroring. This wait type accumulates during mirroring activity. It is used internally so it is not formally documented by Microsoft. As this wait is uncommon low values tend to not be problematic. If moderate values are experienced then investigating other mirroring waits is recommended. Please note that database mirroring is a deprecated feature and could be removed in an upcoming release. Investigation into other high availability and disaster recovery solutions is recommended

Resolved by

DBAs and Developers

Suggested solutions

  1. If transactions on the principal are being delayed (because of high waits) consider switching the mirror mode to asynchronous
  2. Use Windows Performance Monitor to check network latency and whether the connection is over-utilised
  3. Ensure network devices have been configured correctly
  4. Consolidate transactions from row-by-row statements to batch processing. Batch processing generate less messages
  5. Unnecessary index maintenance must be sent across to the mirror (unnecessary messages). Remove any unused indexes from the principal

Additional research

SQL Server blocking caused by database mirroring wait type DBMIRROR_DBM_EVENT
Should you ignore DBMIRROR_DBM_MUTEX?
Troubleshoot Database Mirroring Configuration
Database Mirroring Best Practices and Performance Considerations

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