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

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To decides to abort Beginning of log If To aborts before operation O₁ ends, undo of update to C will be physical To has completed operation O₁ on C, releases lower-level lock; physical undo cannot be done anymore, logical undo will add 100 to C T₁ can update C since To has released lower-level lock on C T₁ releases lower-level lock on C Logical undo of O₁ adds 100 on C O₁ undo complete