442 views

Suppose,

T1: W(X), T2: R(X), T1: W(X), T2: Commit, T1: Abort

Here we can see T2 is getting committed before T1 aborts, so it is clearly an Irrecoverable schedule but is it cascading?

### 1 comment

@DebSujit

Recoverable Schedule – A schedule is said to be recoverable if it is recoverable as name suggest. Only reads are allowed before write operation on same data. Only reads (Ti->Tj) is permissible...

###   https://gateoverflow.in/32150/Number-of-cascadeless-schedules

and if the transaction read or write and then commit and then write that is cascadeless

note:then operation are on same variable

If a transaction lets say T2 makes a dirty read from another transaction T1. Transaction T3 makes another dirty read from T2 and T4 makes a dirty read from T3, Now if T1 somehow crashes before commit and then rollbacks  Then T2 will also rollback so does T3 and T4. This is just like cascading effect and so does the name Cascading schedule. But since Transactions T2, T3 and T4 depends on T1 and have not committed before T1 they can also be rolled back without causing any consistencies. And hence cascading schedules are recoverable.

The only drawback with cascading schedule is they lower the throughput of the systems as crashing of one transaction leads to subsequent rollbacks of other transactions.(Only the transactions which have performed dirty read)

by
If it is irrecoverable schedule,then how it is cascading. Cascading means in some recoverable schedules where an uncommited transaction has to be rolled back . So obvious not cascading.

Suppose eg: w1(x)r2(y)w1(x)a2c1

it is obvious recoverable because T2 has not commited but aborted but not cascadeless because there is phenomenon od cascading ..since T2 will be aborted or rolled back

1
3,597 views
2
929 views
1 vote
3
265 views