The Mirror Commit Overhead (Milliseconds) alert indicates that the commit overhead (in MS) of the mirrored database reached or exceeded an alert threshold. Specifies the number of milliseconds of average delay per transaction that are tolerated before a warning is generated on the principal server. This delay is the amount of overhead incurred while the principal server instance waits for the mirror server instance to write the transaction's log record into the redo queue. This value is relevant only in high-safety mode.

This alert is raised based on the diagnostic data collection interval specified in Server Properties. For more information, see Set general server options.

For more information about mirror commit overhead, see the Microsoft document, Use Warning Thresholds and Alerts on Mirroring Performance Metrics (SQL Server).

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