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Transaction Scopes..

  • January 18, 2012 at 7:36 am

    #263041

    I have 2 questions here.

    1. What is the scope of read uncommited transaction isolation - will it be across the session ?

    2. Difference between NOLOCK and READUNCOMMITED ( i need to use one of it where, a select query involving multiple databases with multiple subqueries ) - upto 10 concurrent users possible and frequent modification of datas possible.

    Regards,

    Santhosh.

  • January 18, 2012 at 7:44 am

    #1435244

    santhosh_ms3 (1/18/2012)

    I have 2 questions here.

    1. What is the scope of read uncommited transaction isolation - will it be across the session ?

    From the point you enable it to the point you enable another isolation level or terminate the session.

    2. Difference between NOLOCK and READUNCOMMITED

    None.

    ( i need to use one of it where, a select query involving multiple databases with multiple subqueries ) - upto 10 concurrent users possible and frequent modification of datas possible.

    And your users are happy with the chance of duplicate data, missing data and dirty data?

    See - http://sqlblog.com/blogs/andrew_kelly/archive/2009/04/10/how-dirty-are-your-reads.aspx

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

  • January 18, 2012 at 8:57 am

    #1435322

    Thanks a lot. Got it.

    To be precise now, The query used to take only 15 to 20 seconds when no other users are available whereas when all are available its running more than 75 min with read uncommited mode enabled. can you suggest? - for me dirty reads are acceptable.

    Regards,

    Santhosh.

  • January 18, 2012 at 9:34 am

    #1435363

    Are your users happy with getting duplicate data, entire sets of rows multiple times? Have they been asked?

    Have you considered one of the snapshot isolation levels? Have you tuned the queries?

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

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