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Thread: Checkpoints

  1. #1
    Join Date
    Feb 2004
    Bangalore, India

    Unanswered: Checkpoints

    the post, SQL Server: Understanding Logging and Recovery in SQL Server
    says "One common misconception about checkpoints is that they only write out pages with changes from committed transactions. This is not true—a checkpoint always writes out all dirty pages, regardless of whether the transaction that changed a page has committed or not."

    If the transaction rolls back after a checkpoint, how will the changes be reverted?



  2. #2
    Join Date
    Feb 2004
    One Flump in One Place
    The transaction log is written to too. Whether the pages are on disk or only in memory makes no difference logically it is only the location that changes would need to be applied in the event of a roll back that is different.
    pootle flump
    ur codings are working excelent.

  3. #3
    Join Date
    Jul 2003
    San Antonio, TX
    The "HOW" question is for Storage Management development team at MS, and I don't think you'll get a complete answer. But what is important to recognize, is that EVERYTHING that alters data AND metadata within the instance, goes through a transaction log of the corresponding database, AND stays there until a CHECKPOINT or a transaction log backup occurs on that database. If that database is in SIMPLE recovery mode, the checkpoint will free the log space from committed and rolled back transactions. Else (if it's FULL or BULK-LOGGED), - only trx log back can remove those transactions, and only if replication has propagated them to subscribers, if replication is setup, or only when the mirror got updated if mirroring is in place.
    "The data in a record depends on the Key to the record, the Whole Key, and
    nothing but the Key, so help me Codd."

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