HikariPool-1 Connection is not available, request timed out after 30002ms.

After some SQL queries, the system is unable to get any connection from the HikariPool and prompts the following error message

HikariPool-1 - Connection is not available, request timed out after 30002ms.

Tested with

• HikariCP 3.3.1
• mysql-connector-java 5.1.47
• Java 8

1. Solution

1.1 Enable the debug logs for com.zaxxer.hikari, it will print out many useful info.

	<!-- this config is for logback framework -->
	<logger name="com.zaxxer.hikari" level="debug" additivity="false">
        <appender-ref ref="STDOUT"/>
    </logger>

2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - HikariPool-1 - configuration:
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - allowPoolSuspension.............false
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - autoCommit......................true
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - catalog.........................none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - connectionInitSql...............none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - connectionTestQuery.............none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - connectionTimeout...............30000
//...
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - jdbcUrl.........................jdbc:mysql://192.168.1.4:3306/wordpress
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - leakDetectionThreshold..........0
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - maxLifetime.....................1800000
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - maximumPoolSize.................1
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - metricRegistry..................none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - metricsTrackerFactory...........none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - minimumIdle.....................1
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - password........................<masked>
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - poolName........................"HikariPool-1"
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - readOnly........................false
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - registerMbeans..................false
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - scheduledExecutor...............none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - schema..........................none
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - threadFactory...................internal
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - transactionIsolation............default
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - username........................"mkyong"
2019-03-20 13:46:23 [main] DEBUG com.zaxxer.hikari.HikariConfig - validationTimeout...............5000
2019-03-20 13:47:25 [main] DEBUG com.zaxxer.hikari.pool.HikariPool - HikariPool-1 - Timeout failure stats (total=10, active=10, idle=0, waiting=0)
2019-03-20 13:47:25 [main] ERROR c.mkyong.calculator.StartApplication - [Exception] : HikariPool-1 - Connection is not available, request timed out after 30001ms.

1.2 By default, the connectionTimeout is 30 seconds.

HikariPool-1 - Connection is not available, request timed out after 30001ms.

1.3 This means Hikari pool reached maximum connections total=10, active=10

HikariPool-1 - Timeout failure stats (total=10, active=10, idle=0, waiting=0)

1.4 Mostly is connection leak, normally this is caused by the connection is not closed after borrowing from the pool.

For example, below code, getConnection() is not close, and this will cause connection leak.

	@Override
    public void update(int postId, String metaValue) throws SQLException {
        try (PreparedStatement ps = 
				dataSource.getConnection().prepareStatement(SQL_UPDATE_POST_META)) {
            ps.setString(1, metaValue);
            ps.setInt(2, postId);
            ps.setString(3, GlobalUtils.META_KEY);
            ps.executeUpdate();
        } catch (SQLException e) {
            logger.error("[UPDATE] [POST_ID] : {}, [META_VALUE] : {}", postId, metaValue);
            throw e;

To fix it, just close the connection.

	@Override
    public void update(int postId, String metaValue) throws SQLException {
        try (Connection connection = dataSource.getConnection();
             PreparedStatement ps = connection.prepareStatement(SQL_UPDATE_POST_META)) {
            ps.setString(1, metaValue);
            ps.setInt(2, postId);
            ps.setString(3, GlobalUtils.META_KEY);
            ps.executeUpdate();
        } catch (SQLException e) {
            logger.error("[UPDATE] [POST_ID] : {}, [META_VALUE] : {}", postId, metaValue);
            throw e;