Schedule With Lock Grants Grants omitted in rest of T T concurrency-control manager chapter lock-X(B) ·Assume grant grant-X(B,T) happens just before read(B) the next instruction B:=B-50 write(B) following lock unlock(B) request lock-S(A) grant-S(A4,T2) ■This schedule is not read() serializable (why?) unlock(4) lock-S(B) A locking protocol is a grant-S(B,T2) set of rules followed by read(B) unlock(B) all transactions while display(4+B) requesting and releasing lock-X(4) locks. grant-X(A,T) read(4) ■Locking protocols A:=A+50 enforce serializability by write() unlock() restricting the set of possible schedules. Database System Concepts-7th Edition 18.6 @Silberschatz,Korth and SudarshanDatabase System Concepts - 7 18.6 ©Silberschatz, Korth and Sudarshan th Edition Schedule With Lock Grants ▪ Grants omitted in rest of chapter • Assume grant happens just before the next instruction following lock request ▪ This schedule is not serializable (why?) ▪ A locking protocol is a set of rules followed by all transactions while requesting and releasing locks. ▪ Locking protocols enforce serializability by restricting the set of possible schedules