Handling of Failures-Site Failure When site Sk recovers,it examines its log to determine the fate of transactions active at the time of the failure. ■Log contain<commit 7下record:site executes redo(T刀 Log contains <abort T>record:site executes undo(7) ■ Log contains <ready T>record:site must consult C;to determine the fate of T. If T committed,redo() ·If T aborted,undo(刀 The log contains no control records concerning T implies that Sk failed before responding to the prepare T message from Ci since the failure of Sk precludes the sending of such a response C;must abort T ·Skmust execute undo(T刀 Database System Concepts-7th Edition 23.11 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.11 ©Silberschatz, Korth and Sudarshan th Edition Handling of Failures - Site Failure When site Sk recovers, it examines its log to determine the fate of transactions active at the time of the failure. ▪ Log contain <commit T> record: site executes redo (T) ▪ Log contains <abort T> record: site executes undo (T) ▪ Log contains <ready T> record: site must consult Ci to determine the fate of T. • If T committed, redo (T) • If T aborted, undo (T) ▪ The log contains no control records concerning T implies that Sk failed before responding to the prepare T message from Ci • since the failure of Sk precludes the sending of such a response Ci must abort T • Sk must execute undo (T)