Dabase Mirroring

  • Hi,

    I have a general question on database mirroring in synchronous mode. As I understand, in this mode a transaction is only commited when the standby server can also commit to it (2phase protocol). But hasn't that an impact on autonomy? What if the standby server would go down? Aren't clients able to commit anymore? Doesn't that run contradictory to the whole idea in the first place? Or does mirroring degrade to asynchronous mode automatically? At the cost of TLogs growing?

    I seem to be missing something here?

    Regards,

    Jan

  • When the mirror database is not available the mirroring session is suspended: the principal stops sending logs to the mirror, yet the processing on the principal continues. The unsent log records are stored in the send queue, ready to be copied over to the mirror as soon as it becomes available.

    This may sound contradictory to the idea of database mirroring, but if the mirror server is not available then the mirroring session in effect does not exist at all. 😉

    More info in Books Online:

    http://msdn2.microsoft.com/en-us/library/ms189901.aspx

    http://msdn2.microsoft.com/en-us/library/ms189284.aspx

    ML

    ---
    Matija Lah, SQL Server MVP
    http://milambda.blogspot.com

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