What happens if an active database connection is left open after work is finished?

Leaving an active database connection open after completing work with it can lead to several issues:

• Resource leak: connections consume memory and other resources of the database server and application.
• Connection pool exhaustion: if the application uses a connection pool, unclosed connections can exhaust the limit, preventing new requests from connecting to the database.
• Performance degradation: a large number of open connections can slow down the database server.
• Potential errors: some transactions may remain incomplete, leading to locks or data inconsistency.

Therefore, it is important to always close connections in a finally block or use try-with-resources constructs (in Java) to ensure resource release:

try (Connection conn = dataSource.getConnection()) {
    // work with the database
} catch (SQLException e) {
    e.printStackTrace();
}
// connection is automatically closed

This ensures stable operation of the application and the database.