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Thread: Isolation Level

  1. #1
    Join Date
    Jan 2003
    Posts
    21

    Unanswered: Isolation Level

    Hi all!!!

    How can I manage to lock a row wich I'm reading to update it, so others can't read it???

    Is this with something called isolation level??
    Can anyone explain me what are de differences between each level (rr, rs,...)??'

    Thank you very much in advance!!!

  2. #2
    Join Date
    Nov 2002
    Posts
    14

    Re: Isolation Level

    DB2 supports the following isolation levels:

    "Repeatable Read"
    "Read Stability"
    "Cursor Stability"
    "Uncommitted Read".

    Repeatable read (RR) locks all the rows an application references within a unit of work. Using repeatable read, a SELECT statement issued by an application twice within the same unit of work in which the cursor was opened, gives the same result each time. With repeatable read, lost updates, access to uncommitted data, and phantom rows are not possible.

    Read stability (RS) locks only those rows that an application retrieves within a unit of work. It ensures that any qualifying row read during a unit of work is not changed by other application processes until the unit of work completes, and that any row changed by another application process is not read until the change is committed by that process. That is, "nonrepeatable read" behavior is not possible.

    Cursor stability (CS) locks any row accessed by a transaction of an application while the cursor is positioned on the row. This lock remains in effect until the next row is fetched or the transaction is terminated. However, if any data on a row is changed, the lock must be held until the change is committed to the database.

    Uncommitted read (UR) allows an application to access uncommitted changes of other transactions. The application also does not lock other applications out of the row it is reading, unless the other application attempts to drop or alter the table. Uncommitted read works differently for read-only and updatable cursors.



    Originally posted by rgarcia
    Hi all!!!

    How can I manage to lock a row wich I'm reading to update it, so others can't read it???

    Is this with something called isolation level??
    Can anyone explain me what are de differences between each level (rr, rs,...)??'

    Thank you very much in advance!!!

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