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Thread: log reads

  1. #1
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    Jul 2009
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    Unanswered: log reads

    When does DB2 need to do log reads?

    Database snap:
    Log pages read = 2608

  2. #2
    Join Date
    May 2003
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    • Rollback (explicitly executed by application or implicitly executed by DB2 when an SQL error is encountered),
    • crash recovery,
    • rollforward logs (usually after a restore).
    • Also, if you have 9.7 and have curr_commit enabled for the database (default on newly created databases) then logs may be read whenever a lockwait situation would otherwise occur to retrieve the state of the data before the lock existed.
    M. A. Feldman
    IBM Certified DBA on DB2 for Linux, UNIX, and Windows
    IBM Certified DBA on DB2 for z/OS and OS/390

  3. #3
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    How about log pages read for HADR replication?

  4. #4
    Join Date
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    Yes, HADR would have to at least read the log buffer, and if HADR was in catch-up mode, log disk reads would be required. I don't know if the snapshot value of log pages read includes the log buffer.

    For that matter, same applies to other processes that read the log buffer or log disk, such as SQL Replication, Q-Replication, CDC (Change Data Capture), etc.

    However, some of log reads may be outside of the DB2 engine and maybe not captured in the database snapshot. The logs are just OS files, and anyone with the correct UNIX permissions can read the files without DB2 knowing about it.

    I am not sure why you are so concerned about it.
    M. A. Feldman
    IBM Certified DBA on DB2 for Linux, UNIX, and Windows
    IBM Certified DBA on DB2 for z/OS and OS/390

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