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Transitioning AlwaysOn Availability Group to Synchronous Commit Mode

  • June 11, 2025 at 2:00 pm

    #4606088

    Hello, I have a SQL Server with an AlwaysOn configuration consisting of three replicas operating in asynchronous commit mode. I have received a request to switch to synchronous commit mode, but I am concerned about potential data loss risks.

    Currently, the database is in "Synchronizing" status. My question is: What will be the status of the Availability Group (AG) if I proceed with the switch to synchronous commit mode?

    Thank you in advance for your help!

    Sans titre

  • June 12, 2025 at 2:10 pm

    #4606632

    Thanks for posting your issue and hopefully someone will answer soon.

    This is an automated bump to increase visibility of your question.

  • June 21, 2025 at 4:57 pm

    #4611158

    If I have understood the question correctly, switching to synchronous commit mode should result in all Availability Groups showing a synchronized status, and the failover readiness state should indicate NO DATA LOSS.

    However, before making this change, it is important to align with the business to identify an appropriate maintenance window or a quiet period on the server. Begin monitoring the replication lag between the primary and secondary replicas immediately after the change. If the secondary replica begins to lag to a point where the business perceives the data as stale or inconsistent with the primary, that becomes your tipping point. At that stage, you will need to investigate the root cause of the lag on the secondary replica.

    If the performance impact is unacceptable, you can revert to asynchronous mode. There is no immediate risk in enabling synchronous commit mode—it does not break anything—but it must be done with caution, close observation, and with a clear rollback plan.

    Thanks,
    Abhinav

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