Consider the following snapshot of the transaction log in Table 1 while three transactions T1, T2 and T3 are executing:

T1: Changing the employee who manages a profile. 

T2: Updating the password of member Penny (LogId 103)

T3: Updating the rating of App 345. 

(a) Using the log information, write SQL statements corresponding to the three transactions. 

(b) Suppose that after logId 109, a system failure occurred. Explain in detail how the system will recover from this system failure. Your explanation should include the actions which will be performed for transactions T1, T2 and T3 when the system restarts and state why these actions are necessary. 

Can anyone explain how to do these questions? 

 

Table 1: Transaction Log Snapshot Logid Transld Operation Table RowId ColumnName Before After 101 TI Start 102 T2 Start 103 T2 Update Member Penny@hotmail.com Password 4#6B myPWD 104 TI Update Profile 28000 Employeeld E55 E89 105 T2 Commit 106 CHKPT TI 107 T3 108 T3 109 T3 233 Start Update Commit Application 345 Rating 3. 4