Degree 0 isolation- Definition - Database

Q.  What is degree 0 isolation?
- Published on 26 Aug 15

a. Transaction does not read dirty data from other transactions.
b. Transaction does not commit any writes until it completes all its writes.
c. Transactions do not dirty data read by a transaction before the transaction commits.
d. A transaction does not overwrite data updated by another user or process.

ANSWER: A transaction does not overwrite data updated by another user or process.

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    Discussion

  • Nirja Shah   -Posted on 02 Nov 15
    - The degree of isolation are divided into four different categories namely
    Degree 0
    Degree 1
    Degree 2
    Degree 3

    Degree 0
    - T i observes degree 0 isolation if it does not overwrite dirty data of T j 's, where i ≠ j.

    - Thus, T i commits its writes before it ends.

    - This means T j may read or write T i 's write and if T i is rolled back then T j has to be rolled-back too.

    - From a recovery viewpoint, degree 0 transactions are not recoverable and also not cascade-free.

    - Example
    Suppose Ti and Tj have the following operations:
    Ti : write (x)
    Tj: write (x)
    History : wi(x)wj(x)

    - If Ti and Tj run concurrently then the final value of x is unpredictable and in some situations cascading may also occur.

    - From recovery point of view degree 0 transactions are not recoverable and for serialization a short lock should be applied to x.

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