The following figure presents five transactions (T₁ until T₅) that are executed more or less simultaneously. Suppose a checkpoint was registered on the logfile at time t_c, marking the last time when pending updates in the database buffer were persisted into the physical database files. Later, at time t_f, a system fault occurred, resulting in loss of the database buffer.

What recovery operations are required?

a. T₁: nothing; T₂: UNDO; T₃: REDO; T₄: REDO; T₅: nothing.

b. T₁: nothing; T₂: REDO; T₃: UNDO; T₄: REDO; T₅: nothing.

c. T₁: REDO; T₂: UNDO; T₃: REDO; T₄: nothing; T₅: nothing.

d. T₁: nothing; T₂: REDO; T₃: REDO; T₄: REDO; T₅: nothing.

Transcribed Image Text:

T₁ 1 T₂ tc checkpoint T3 T4 H T5 tf system fault