Cascading Rollback example

In the example for illustrating cascading roll back, how come the condition for simple 2P lock is satisfying when in T1 - after X-L(A) there is U(A) and in T2 again there is XL(A). As once the unlocking starts no more locking can be allowed in a schedule. i am confused in this. Can anyone please help me to get this correctly??

also can you plz give me a example of successful basic 2 phase locking protocol.

4Comments
Virtual GATE virtualgate 9 May 2017 11:44 am

Can you share the link of the video?

shivani shivani1234 9 May 2017 04:39 pm
  • in the schedule explained in video t1 has unlocked(released lock) on item A and t2 has acquired exclusive lock on A which is correct.
  • according to your query "As once the unlocking starts no more locking can be allowed in a schedule." this is true for a transaction as sir told in video and not for schedule.
  • in schedule there can can be more than one transactions.
  • in simple 2PL , transactions have got constraint that acquiring locks can be done in beginning only and releasing at end.
Punit Dabas punitdabas 9 May 2017 05:49 pm

thanks i get it :)