Data Replication

Data Replication 

Data replication is the process in which the data is copied at multiple locations (Different computers or servers) to improve the availability of data.

Data replication is done with an aim to:

• Increase the availability of data.
• Speed up the query evaluation.

There are two types of data replication:

1. Synchronous Replication:
In synchronous replication, the replica will be modified immediately after some changes are made in the relation table. So there is no difference between original data and replica.

2. Asynchronous replication:
In asynchronous replication, the replica will be modified after commit is fired on to the database.

The three replication schemes are as follows:

1. Full Replication

In full replication scheme, the database is available to almost every location or user in communication network.

Advantages of full replication

• High availability of data, as database is available to almost every location.
• Faster execution of queries.

Disadvantages of full replication

• Concurrency control is difficult to achieve in full replication.
• Update operation is slower.

2. No Replication

No replication means, each fragment is stored exactly at one location.

Advantages of no replication

• Concurrency can be minimized.
• Easy recovery of data.

Disadvantages of no replication

• Poor availability of data.
• Slows down the query execution process, as multiple clients are accessing the same server.

3. Partial replication

Partial replication means only some fragments are replicated from the database.

Advantages of partial replication
The number of replicas created for fragments depend upon the importance of data in that fragment.