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  1. #1
    Join Date
    Aug 2003
    Posts
    33

    Unanswered: increase in deadlocks

    Hi all,

    I am just curious to know why deadlocks and internal rollbacks due to deadlocks were drastically increased when I decreased LOCKTIMEOUT from 120s to 30s. I really appreciate if anyone could provide me with some explanation.

    Thanks,
    mc

  2. #2
    Join Date
    May 2003
    Location
    USA
    Posts
    5,737
    First of all, a deadlock is not the same as lock contention, which unfortunately has been confused by the IBM folks in Toronto (DB2 for Windows, UNIX, and LINUX), even though the IBM folks in Santa Teresa (DB2 390) explain it correctly and always differentiate the two concepts.

    If you were getting a true deadlock (also known as a deadly embrace), then changing the LOCKTIMEOUT would have no effect. But if you have lock contention, then decreasing the amount of time that an application waits for a lock to be released by another thread will cause more rollbacks when the elapsed lock wait time has completed. I think it is intuitively obvious why this is case, but if it is not clear, then please advise.

  3. #3
    Join Date
    Aug 2003
    Posts
    33

    Thanks Marcus & need more help with deadlocks

    Originally posted by Marcus_A
    First of all, a deadlock is not the same as lock contention, which unfortunately has been confused by the IBM folks in Toronto (DB2 for Windows, UNIX, and LINUX), even though the IBM folks in Santa Teresa (DB2 390) explain it correctly and always differentiate the two concepts.

    If you were getting a true deadlock (also known as a deadly embrace), then changing the LOCKTIMEOUT would have no effect. But if you have lock contention, then decreasing the amount of time that an application waits for a lock to be released by another thread will cause more rollbacks when the elapsed lock wait time has completed. I think it is intuitively obvious why this is case, but if it is not clear, then please advise.



    Thanks Marcus for the information. I understood your point.

    Will u please help me how to find out the nature of deadlocks and how to reduce it . My databases are giving me a hard time with deadlocks.

    mc

  4. #4
    Join Date
    Aug 2001
    Location
    UK
    Posts
    4,650

    Re: Thanks Marcus & need more help with deadlocks

    Activate the deadlock event moitor ...

    Cheers

    Sathyaram


    Originally posted by mcdb2
    Thanks Marcus for the information. I understood your point.

    Will u please help me how to find out the nature of deadlocks and how to reduce it . My databases are giving me a hard time with deadlocks.

    mc
    Visit the new-look IDUG Website , register to gain access to the excellent content.

  5. #5
    Join Date
    Aug 2003
    Posts
    33

    Re: Thanks need more help with deadlocks

    Originally posted by sathyaram_s
    Activate the deadlock event moitor ...

    Cheers

    Sathyaram

    Thanks Sathyaram. I will do it
    mc

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