in Databases
3,099 views
3 votes
3 votes
in Databases
by
3.1k views

1 Answer

7 votes
7 votes
Best answer

Checkpoint: Checkpoint is a mechanism where all the previous logs are removed from the system and stored permanently in a storage disk. Checkpoint declares a point before which the DBMS was in consistent state, and all the transactions were committed.

Recovery:When a system with concurrent transactions crashes and recovers, it behaves in the following manner −

  • The recovery system reads the logs backwards from the end to the last checkpoint.
  • It maintains two lists, an undo-list and a redo-list.
  • If the recovery system sees a log with <tn, start=""> and <tn, commit=""> or just  <tn, commit="">, it puts the transaction in the redo-list.
  • If the recovery system sees a log with <tn, start=""> but no commit or abort log found, it puts the transaction in undo-list.

All the transactions in the undo-list are then undone and their logs are removed. All the transactions in the redo-list and their previous logs are removed and then redone before saving their logs

selected by

4 Comments

Thank you very much.. it helped a lot. I don't know why most of the books are giving option C as answer for the 1st question.
1
1
Doesn't it depend on recovery algorithm we choose:
deffered update or immediate update?
0
0
@skyby it depends
0
0