Transactions-Weaker isolation levels:

Consider two tables R(A,B) and S(C). Below are pairs of transactions. Compute what values will be reported by the read statements of weaker isolation levels. Assume individual statements are executed atomically. (a) Transaction 1:

Set Transaction Isolation Level Read Uncommitted;

Select count(*) From R;

Select count(*) From S;

Commit;

Transaction 2:

Set Transaction Isolation Level Serializable;

Insert Into R Values (1,2);

Insert Into S Values (3);

Commit;

(b) Transaction 1:

Set Transaction Isolation Level Read Committed;

Select count(*) From R;

Select count(*) From S;

Commit;

Transaction 2:

Set Transaction Isolation Level Serializable;

Insert Into R Values (6,2);

Insert Into R Values (3,4);

Insert Into S Values (5);

Insert Into S Values (4);

Commit;

(c) Transaction 1:

Set Transaction Isolation Level Repeatable Read;

Select count(*) From R;

Select count(*) From S;

Select count(*) From R;

Commit;

Transaction 2:

Set Transaction Isolation Level Serializable;

Insert Into R Values (1,2);

Select * From R;

Commit;