填空题

[问题2] 各个事务的内部结构如下所示。若事务不施加任何锁，则有多少可能的调度。
T1: R1 ( Get A into t1 ;t1: = t1 + 1 ); U1 ( Update A from t1 );
T2: R2 ( Get A into t2 ;t2: = t2 * 2); U2 ( Update A from t2);
T3:1t3 ( Get A into t3; display t3 ); U3 ( Update A from 1 );