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Describe the differences between the pessimistic SERIALIZABLE model and the optimistic SNAPSHOT model in terms of transactional isolation

    Question

  •  Describe the differences between the pessimistic SERIALIZABLE model and the optimistic SNAPSHOT model in terms of transactional isolation (i.e., not the concurrency differences, but instead how the exact same transactional modifications may result in different final outcomes).

    plz answer this question

    • Moved by Eileen Zhao Tuesday, November 20, 2012 6:15 AM (From:SQL Server Integration Services)
    Sunday, November 18, 2012 2:21 PM

Answers

  • Hi venkat,

    SERIALIZABLE
    Specifies the following:
    Statements cannot read data that has been modified but not yet committed by other transactions.
    No other transactions can modify data that has been read by the current transaction until the current transaction completes.
    Other transactions cannot insert new rows with key values that would fall in the range of keys read by any statements in the current transaction until the current transaction completes.

    SNAPSHOT
    Specifies that data read by any statement in a transaction will be the transactionally consistent version of the data that existed at the start of the transaction. The transaction can only recognize data modifications that were committed before the start of the transaction. Data modifications made by other transactions after the start of the current transaction are not visible to statements executing in the current transaction. The effect is as if the statements in a transaction get a snapshot of the committed data as it existed at the start of the transaction.

    For more information, please refer to SET TRANSACTION ISOLATION LEVEL (Transact-SQL): http://msdn.microsoft.com/en-us/library/ms173763.aspx.

    Thanks.


    Maggie Luo
    TechNet Community Support

    Sunday, November 25, 2012 11:07 AM

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