Briefly describe concurrency execution, Database Management System

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Briefly describe concurrency execution?

Lock - based protocols

Locks

There are several modes in which a data item may be locked in this section we restrict our attention to two modes

Ø Shared

Ø Exclusive

T1 : lock - x(B );

read(B);

B:=B-50;

write(B);

unlock(B);

Lock-x(A);

read(A);

A:=A+50;

write(A);

unlock(A).

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