Explain about conflict serializability in DBMS

Conflict serializability orders any conflicting operations in the same way as some serial execution. A pair of operations is said to conflict if they operate on the same data item and one of them is a write operation.

That means

• Readi(x) readj(x) - non conflict   read-read operation

• Readi(x) writej(x) - conflict         read-write operation.

• Writei(x) readj(x) - conflic      t write-read operation.

• Writei(x) writej(x) - conflict      write-write operation.

Where I and j denote two different transactions Ti and Tj.

Precedence graph

It is used to check conflict serializability.

The steps to check conflict serializability are as follows −

• For each transaction T, put a node or vertex in the graph.

• For each conflicting pair, put an edge from Ti to T_j.

• If there is a cycle in the graph then schedule is not conflict serializable else schedule is conflict serializable.

Example 1

The cycle is present so it is not conflict serializable.

Example 2

The cycle is not present, so it is conflict serializable.

Example 3

The cycle is not present, so it is conflict serializable.