Self Doubt

Question

Start T;

Write(A);

Checkpoint;

Commit;

System Crash;

Consider the above transaction T. Suppose the system crashes after the performing the above transaction.Will the recovery manager keep the above transaction into Redo-list ,if yes then what statement will be kept into redo-list?

Comments

@shubhanshu i don't think the transaction will be redone since there is a commit operation in the transaction and as soon as the commit statement is encountered ,the operations before checkpoint will be saved immediately to the database permanently.So there is no statement left after checkpoint which could be redone.

---

To solve this problem we need to follow certain steps :-

Read the log file backwards up to the checkpoint (not before it) :-

1) If you find (commit, Ti) , add Ti to Redo-list.

2) If you find (start, Tj), add Tj to Undo-list. (Here note that Tj is a transaction which has only started and not committed i.e. no (commit, Tj) is found before (start, Tj) while retracing backwards).

3) Suppose there was a transaction which started before checkpoint but has not committed either before or after the checkpoint. Now how will we get to know about it as we can't go before checkpoint? Here is a thing we need to know that checkpoint maintains a list of all active transactions. Add such transaction to the Undo-list.

Since your question matches with the 1st step only so put T in the Re-do list.

what statement will be kept into redo-list

The whole transaction needs to be re done. Not any particular statement.

Re-do list: {T}

Try to solve this (will make it clearer): https://gateoverflow.in/8246/gate2015-2-46

---

@MINIPanda Thank you.