Intension shared lock in DBMS

In a database management system (DBMS), an intention shared (IS) lock is a type of lock used to manage concurrent access to database resources. It is typically used when multiple transactions need to read data simultaneously without conflicting with each other.

Let's consider a simple example to understand the concept of an intention shared lock:

Imagine a database with a table called "Products" that stores information about various products. The table has several columns, including "ProductID," "ProductName," and "ProductPrice." Multiple users or transactions can access this table concurrently.

Suppose we have two transactions, T1 and T2, running simultaneously. Both transactions want to read the data from the "Products" table, but they do not intend to modify the data.

1. Transaction T1 starts and wants to read the "ProductName" and "ProductPrice" of a specific product with ProductID=100. It requests an intention shared (IS) lock on the "Products" table.

2. At the same time, transaction T2 starts and wants to read the "ProductPrice" of all products in the table. It also requests an intention shared (IS) lock on the "Products" table.

3. The DBMS checks if any conflicting locks exist on the "Products" table. Since both transactions only intend to read the data without modifying it, they can be granted the IS locks simultaneously.

4. Transaction T1 acquires the IS lock, indicating its intention to read data from the "Products" table. It then reads the "ProductName" and "ProductPrice" of the product with ProductID=100.

5. Transaction T2 also acquires the IS lock and reads the "ProductPrice" of all products in the table.

By using the intention shared (IS) locks, multiple transactions can access the data concurrently for reading purposes without blocking each other. The IS lock indicates the intention to read and allows other transactions with the same intention to proceed simultaneously.

It's important to note that intention shared (IS) locks are compatible with each other but incompatible with exclusive locks (used for write operations). This means that transactions holding IS locks will not block other transactions intending to read the data but will block transactions intending to modify (write) the data.

In summary, intention shared locks in a DBMS allow multiple transactions to concurrently read data without conflicting with each other, ensuring efficient and concurrent access to the database resources.