How to Prevent JDBC MySQL Connection Pool Exhaustion?

Practices to Prevent Exhaustion of JDBC MySql Connection Pools

Connection Pool Exhaustion in MySql

Connection pools aim to enhance application performance by reusing database connections, thereby avoiding the overhead of establishing new connections each time. However, when database connections are not properly managed, it can lead to the exhaustion of the connection pool.

Case Study: Connection Pool Exhaustion

A Java-JSF application faces connection pool exhaustion due to improper connection handling. The application retrieves connections from a connection pool managed by the GlassFish application server. After extensive database operations, the application experiences the following error:

RAR5117 : Failed to obtain/create connection from connection pool [ mysql_testPool ]. Reason : In-use connections equal max-pool-size and expired max-wait-time. Cannot allocate more connections.

Cause: Database Connection Leaks

The root cause of the connection pool exhaustion is database connection leaks. Connections are not properly closed after use, leading to their indefinite retention in the pool. Each unclosed connection consumes a slot in the pool, eventually depleting it and preventing the application from acquiring additional connections.

Solution: Proper Connection Handling

To resolve the connection pool exhaustion, it is crucial to ensure the proper handling of database connections. This can be achieved by using a try-with-resources block to acquire and close connections within the same method block, ensuring that connections are always closed, even in the presence of exceptions.

public void create(Entity entity) throws SQLException {
    try (
        Connection connection = dataSource.getConnection();
        PreparedStatement statement = connection.prepareStatement(SQL_CREATE);
    ) { 
        statement.setSomeObject(1, entity.getSomeProperty());
        // ...
        statement.executeUpdate();
    }
}

Alternatively, if using Java 7 or earlier, try-finally blocks can be employed:

public void create(Entity entity) throws SQLException {
    Connection connection = null;
    PreparedStatement statement = null;

    try { 
        connection = dataSource.getConnection();
        statement = connection.prepareStatement(SQL_CREATE);
        statement.setSomeObject(1, entity.getSomeProperty());
        // ...
        statement.executeUpdate();
    } finally {
        if (statement != null) try { statement.close(); } catch (SQLException logOrIgnore) {}
        if (connection != null) try { connection.close(); } catch (SQLException logOrIgnore) {}
    }
}

Importance of Connection Closures

It is essential to understand that even when utilizing connection pools, it is the responsibility of the application developer to manually close connections. Connection pools do not automatically handle connection closures. Instead, they typically employ a wrapped connection approach, where the connection close() method checks if the connection is eligible for reuse before actually closing it.

Therefore, neglecting to close connections can result in the accumulation of unused connections within the pool, leading to its exhaustion and subsequent application crashes. Proper connection handling is crucial for maintaining the health and efficiency of JDBC connection pools.

The above is the detailed content of How to Prevent JDBC MySQL Connection Pool Exhaustion?. For more information, please follow other related articles on the PHP Chinese website!