Transactions 2: Serializability

A (possibly concurrent) schedule is serializable if it is ....

• executed in a real time manner

• always gives the same result

• executed serially

• equivalent to a serial schedule

We can identify a serializable schedule by checking the following notions ...

• Conflict serializability

• View serializability

• Recoverable serializability

• Concurrent serializability

The following instructions are conflicts if executed consecutively, except..

• l_i = read(Q), l_j = read(Q)

• l_i = read(Q), l_j = write(Q)

• l_i = write(Q), l_j = read(Q)

• l_i = write(Q), l_j = write(Q)

If a schedule S can be transformed into a schedule S’ by a series of swaps of non-conflicting instructions, we say that S and S’ are ..

• conflict serializable

• conflict equivalent

• conflict serializability

• conflict

A schedule S that conflict equivalent to a serial schedule is called ..

• conflict serializable

• conflict equivalent

• conflict serializability

• conflict

Examine the following schedules.

Schedule 3 is conflict serializable.

• True

• False

Examine the following schedule.

The schedule is not conflict serializable.

• True

• False

Let S and S’ be two schedules with the same set of transactions. S and S’ are view equivalent if the following three conditions are met, for each data item Q,

• The transaction (if any) that performs the final write(Q) operation in schedule S must also perform the final write(Q) operation in schedule S’.

• If in schedule S, transaction T_i reads the initial value of Q, then in schedule S’ also transaction T_i must read the initial value of Q

• If in schedule S transaction T_i executes read(Q), and that value was produced by transaction T_j (if any), then in schedule S’ also transaction T_i must read the value of Q that was produced by the same write(Q) operation of transaction T_j .

• If in schedule S, transaction T_i write the initial value of Q, then in schedule S’ also transaction T_i must write the initial value of Q

Every view serializable schedule is also conflict serializable

• True

• False

The following schedule is not a recoverable schedule.

• True

• False