How do you ensure data consistency in RDBMS?

Data consistency in RDBMS is ensured through the use of ACID properties, constraints, normalisation, and transaction management.

ACID properties are a set of principles that guarantee that database transactions are processed reliably. ACID stands for Atomicity, Consistency, Isolation, and Durability. Atomicity ensures that all operations within a transaction are completed successfully; if not, the transaction is aborted. Consistency ensures that a transaction brings the database from one valid state to another. Isolation ensures that concurrent execution of transactions leaves the database in the same state that would have been obtained if the transactions were executed sequentially. Durability ensures that once a transaction has been committed, it will remain committed even in the case of a system failure.

Constraints are rules enforced on data columns in a table. They ensure the accuracy and reliability of the data in the table. Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table. Common constraints include NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK.

Normalisation is a database design technique that reduces data redundancy and eliminates undesirable characteristics like Insertion, Update and Deletion Anomalies. It divides larger tables into smaller tables and links them using relationships. The main aim of normalisation is to add, delete or modify a field that can be made in a single table, then propagated through the rest of the database via the defined relationships.

Transaction management is crucial for maintaining consistency in a database. A transaction is a single logical unit of work that accesses and possibly modifies the contents of a database. Transactions access data using read and write operations. To maintain consistency, changes made by an incomplete transaction must not be visible to others. Furthermore, a completed transaction should persist, even in the event of failures. This is achieved by using log files to record all changes.

In conclusion, ensuring data consistency in RDBMS involves a combination of ACID properties, constraints, normalisation, and transaction management. These techniques work together to maintain the integrity and reliability of the data.