What is a database connection pool and why is it needed?

A database connection pool is a mechanism for managing a set of open connections to a database, which are reused by the application instead of creating a new connection for each request.

Why it is needed:

• Performance improvement: creating a new database connection is a time-consuming and resource-intensive operation. The pool allows the reuse of already open connections.
• Limiting the number of connections: a database can support a limited number of simultaneous connections. The pool controls their number, preventing overload.
• Resource management: the pool automatically closes unused connections and restores 'broken' ones.

Example of using a pool in Java with HikariCP:

HikariConfig config = new HikariConfig();
config.setJdbcUrl("jdbc:mysql://localhost:3306/mydb");
config.setUsername("user");
config.setPassword("password");
config.setMaximumPoolSize(10); // maximum 10 connections

HikariDataSource ds = new HikariDataSource(config);

try (Connection conn = ds.getConnection()) {
    // work with the database
}

Thus, the connection pool improves stability and efficiency when working with a database in applications.