What is conflict serializability in SQL ?

Overview

Serializability is bascially used to ensure that transactions are executing in a correct way without any interruption.

• Serializability allows the database to be in a consistent state.

• Serializability is generally used in the transactions.

Serializability is of two types:

• Conflict serializability
• View serializability

Conflict serializability occurs when two instructions conflict for a single data item.

There will be no conflict if we read the data, but there will be a conflict if we write the data.

Instructions O i and O j are the transactions of Ti and Tj respectively. Then there exists a conflict if some item Q accessed by both O i and O j. At least one of these instructions writes Q.

1. O i = read(Q), O j = read(Q). O i and O j don’t conflict.

2. O i = read(Q), O j = write(Q). They conflict.

3. O i = write(Q), O j = read(Q). They conflict.

4. O i = write(Q), O j = write(Q). They conflict.

If a schedule S can be converted into a schedule S ´ by a series of swaps of non-conflicting instructions, we say that S and S ´ conflict equivalent.

• Here S and S’ are conflict equivalent.

• The order of each pair of conflicting operations in S and S` is the same.