How does the locking mechanism in DB2 operate?

The locking mechanism in DB2 controls concurrent access to the database by locking database objects such as tables, rows, or pages. DB2 supports various types of locks including shared locks, exclusive locks, and update locks.

In DB2, when a transaction reads or writes to a database object, it requests the appropriate lock. Depending on the transaction’s needs and the type of lock, DB2 will lock the database object accordingly. For example, when a transaction needs to read data from a table, it will request a shared lock, allowing other transactions to still read the data from the table but not write to it.

If a transaction needs to perform a write operation on a database object, it requests an exclusive lock which prevents other transactions from reading or writing to that object until the transaction releases the lock. An update lock is a special type of lock used to prevent other transactions from performing write operations while reading data.

DB2’s locking mechanism follows the ACID (Atomicity, Consistency, Isolation, and Durability) transaction properties, ensuring the integrity and consistency of transaction operations. When a transaction needs to access a database object, DB2 will determine how to lock the object based on the transaction’s isolation level and the type of lock, to ensure the correctness and effectiveness of concurrent access.