What are the advantages and drawbacks of multiversion timestamp ordering in comparison with ordinary timestamp ordering?
What will be an ideal response?
The algorithm allows more concurrency than single version timestamp ordering but incurs additional storage costs.
Advantages:
The presence of multiple committed versions allows late read operations to succeed.
write operations are allowed to proceed immediately unless they will invalidate earlier reads (a write by a transaction with timestamp Ti is rejected if a transaction with timestamp Tj has read a data item with write timestamp Tk and Tk < Ti < Tj).
Drawbacks:
The algorithm requires storage for multiple versions of each committed objects and for information about the read and write timestamps of each version to be used in carrying out the read and write rules. In the case that a version is deleted, read operations will have to be rejected and transactions aborted.
Exercise shows that the algorithm can provide yet more concurrency, at the risk of cascading aborts, by allowing read operations to proceed immediately. In this case, to ensure recoverability, requests to commit must be delayed until any the completion (commitment or abortion) of any transaction whose tentative objects have been observed.
You might also like to view...
When you open a copy of a template in the form of a new Word document, the title bar indicates Template followed by a number
Indicate whether the statement is true or false
Combining interactive data entry with the repetition capabilities of the while statement produces rigidly-defined programs.
Answer the following statement true (T) or false (F)
The correct command to allow user Thompson to delete rows in the CUSTOMER table would be: GRANT ____ ON CUSTOMER TO THOMPSON.
A. DROP B. REMOVE C. UPDATE D. DELETE
According to the secure password guidelines, which of the following would be considered a secure password?
A. password B. My_Password C. My_Passw0rd D. my_passw0rd