Consider the log in Figure 19.7. Suppose there is a crash during recovery, just before the operation abort log record is written for operation O1. Explain what will happen when the system recovers again.

Figure 19.7

To decides to abort Beginning of log If To aborts before operation O ends, undo of update to C will be physical To has completed operation O on C, releases lower-level lock; physical undo cannot be done anymore, logical undo will add 100 to C T can update C since To has released lower-level lock on C T releases lower-level lock on C Logical undo of O adds 100 on C O undo complete