HikariCP ^{It's Faster.}  

Hi·ka·ri [hi·ka·'lē] (Origin: Japanese): light; ray.

There is nothing faster. There is nothing more correct. HikariCP is a "zero-overhead" production-quality connection pool. Coming in at roughly 50Kb, the library is extremely light. Read about how we do it here.

Maven Repository

    <dependency>
        <groupId>com.zaxxer</groupId>
        <artifactId>HikariCP</artifactId>
        <version>1.3.6</version>
        <scope>compile</scope>
    </dependency>

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Thank you!
We just wanted to say "Thank you!" for all of your support. As you can see, you have all helped HikariCP off to a great start over the past few months. The momentum is here.

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JMH Benchmarks

Using the excellent JMH microbenchmark framework developed by the Oracle JVM performance team, extremely accurate microbenchmarks were created to isolate and measure the overhead of HikariCP and other popular pools. You can checkout the HikariCP benchmark project for details and review/run the benchmarks yourself.

• One Connection Cycle is defined as single DataSource.getConnection()/Connection.close().
  • In Unconstrained benchmark, connections > threads.
  • In Constrained benchmark, threads > connections (2:1).
• One Statement Cycle is defined as single Connection.prepareStatement(), Statement.execute(), Statement.close().

¹ BoneCP fails to complete Statement Cycle benchmark unless the "CACHED" pool strategy is used.
² Tomcat fails to complete Statement Cycle benchmark when "StatementFinalizer" feature is enabled.
³ Benchmark results run against 1.3.3

What's up with other pools?

Not all pools are created equal. Read our pool analysis here if you care to know the good, bad, and ugly.

You're [probably] doing it wrong.

AKA "What you probably didn't know about connection pool sizing". Read on to find out.

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Configuration (knobs, baby!)

The following are the various properties that can be configured in the pool, their behavior, and their defaults. Rather than coming out of the box with almost nothing configured, HikariCP comes with sane defaults that let a great many deployments run without any additional tweaking (except for the DataSource and DataSource properties).

^📎 HikariCP uses milliseconds for all time values.

✅autoCommit
This property controls the default auto-commit behavior of connections returned from the pool. It is a boolean value. Default: true

🔤catalog
This property sets the default catalog for databases that support the concept of catalogs. If this property is not specified, the default catalog defined by the JDBC driver is used. Default: none

🔤connectionInitSql
This property sets a SQL statement that will be executed after every new connection creation before adding it to the pool. If this SQL is not valid or throws an exception, it will be treated as a connection failure and the standard retry logic will be followed. Default: none

🔤connectionTestQuery
This is for "legacy" databases that do not support the JDBC4 Connection.isValid() API. This is the query that will be executed just before a connection is given to you from the pool to validate that the connection to the database is still alive. It is database dependent and should be a query that takes very little processing by the database (eg. "VALUES 1"). See the jdbc4ConnectionTest property for a more efficent alive test. One of either this property or jdbc4ConnectionTest must be specified. Default: none

⌚connectionTimeout
This property controls the maximum number of milliseconds that a client (that's you) will wait for a connection from the pool. If this time is exceeded without a connection becoming available, a SQLException will be thrown. Default: 30000 (30 seconds)

➡️dataSource
This property is only available via programmatic configuration. This property allows you to directly set the instance of the DataSource to be wrapped by the pool, rather than having HikariCP construct it via reflection. When this property is specified, the dataSourceClassName property and all DataSource-specific properties will be ignored. Default: none

🔤dataSourceClassName
This is the name of the DataSource class provided by the JDBC driver. Consult the documentation for your specific JDBC driver to get this class name, or see the table below. Note XA data sources are not supported. XA requires a real transaction manager like bitronix. Note that you do not need this property if you are using driverClassName to wrap an old-school DriverManager-based JDBC driver. The HikariCP team considers dataSourceClassName to be a superior method of creating connections compared to driverClassName. Default: none

🔤driverClassName
This property allows HikariCP to wrap an old-school JDBC driver as a javax.sql.DataSource. It is unnecessary when using the dataSourceClassName property, which is the preferred way of creating connections in HikariCP. DataSources are provided by all but the oldest JDBC drivers. If driverClassName is used, then the jdbcUrl property must also be set. Default: none

⌚idleTimeout
This property controls the maximum amount of time (in milliseconds) that a connection is allowed to sit idle in the pool. Whether a connection is retired as idle or not is subject to a maximum variation of +30 seconds, and average variation of +15 seconds. A connection will never be retired as idle before this timeout. A value of 0 means that idle connections are never removed from the pool. Default: 600000 (10 minutes)

❎initializationFailFast
This property controls whether the pool will "fail fast" if the pool cannot be seeded with initial connections successfully. If connections cannot be created at pool startup time, a RuntimeException will be thrown from the HikariDataSource constructor. This property has no effect if minimumPoolSize is 0. Default: false

❎isolateInternalQueries
This property determines whether HikariCP isolates internal pool queries, such as the connection alive test, in their own transaction. Since these are typically read-only queries, it is rarely necessary to encapsulate them in their own transaction. This property only applies if autoCommit is disabled. Default: false

✅jdbc4ConnectionTest
This property is a boolean value that determines whether the JDBC4 Connection.isValid() method is used to check that a connection is still alive. This value is mutually exclusive with the connectionTestQuery property, and this method of testing connection validity should be preferred if supported by the JDBC driver. Default: true

🔤jdbcUrl
This property is only used when the driverClassName property is used to wrap an old-school JDBC driver as a javax.sql.DataSource. While JBDC URLs are popular, HikariCP does not recommend using them. The DataSource implementation provided by your driver provides bean properties for all the driver parameters that used to be specified in the JDBC URL. Before using the jdbcUrl and driverClassName because that's the way you've always done it, consider using the more modern and maintainable dataSourceClassName approach instead. Note that if this property is used, you may still use DataSource properties to configure your driver and is in fact recommended. Default: none

⌚leakDetectionThreshold
This property controls the amount of time that a connection can be out of the pool before a message is logged indicating a possible connection leak. A value of 0 means leak detection is disabled. While the default is 0, and other connection pool implementations state that leak detection is "not for production" as it imposes a high overhead, at least in the case of HikariCP the imposed overhead is only 5μs (microseconds) split between getConnection() and close(). Maybe other pools are doing it wrong, but feel free to use leak detection under HikariCP in production environments if you wish. Default: 0

⌚maxLifetime
This property controls the maximum lifetime of a connection in the pool. When a connection reaches this timeout, even if recently used, it will be retired from the pool. An in-use connection will never be retired, only when it is idle will it be removed. We strongly recommend setting this value, and using something reasonable like 30 minutes or 1 hour. A value of 0 indicates no maximum lifetime (infinite lifetime), subject of course to the idleTimeout setting. Default: 1800000 (30 minutes)

#️⃣maximumPoolSize
This property controls the maximum size that the pool is allowed to reach, including both idle and in-use connections. Basically this value will determine the maximum number of actual connections to the database backend. A reasonable value for this is best determined by your execution environment. When the pool reaches this size, and no idle connections are available, calls to getConnection() will block for up to connectionTimeout milliseconds before timing out. Default: 10

#️⃣minimumIdle
This property controls the minimum number of idle connections that HikariCP tries to maintain in the pool. If the idle connections dip below this value, HikariCP will make a best effort to add additional connections quickly and efficiently. However, for maximum performance and responsiveness to spike demands, we recommend not setting this value and instead allowing HikariCP to act as a fixed size connection pool. Default: same as maximumPoolSize

🔤password
This property sets the default authentication password used when obtaining Connections from the underlying driver. Default: none

🔤poolName
This property represents a user-defined name for the connection pool and appears mainly in a JMX management console to identify pools and pool configurations. Default: auto-generated

❎readOnly
This property controls whether Connections obtained from the pool are in read-only mode by default. Note some databases do not support the concept of read-only mode, while others provide query optimizations when the Connection is set to read-only. Whether you need this property or not will depend largely on your application and database. Default: false

❎registerMbeans
This property controls whether or not JMX Management Beans ("MBeans") are registered or not. Default: false

🔤transactionIsolation
This property controls the default transaction isolation level of connections returned from the pool. If this property is not specified, the default transaction isolation level defined by the JDBC driver is used. Typically, the JDBC driver default transaction isolation level should be used. Only use this property if you have specific isolation requirements that are common for all queries, otherwise simply set the isolation level manually when creating or preparing statements. The value of this property is the constant name from the Connection class such as TRANSACTION_READ_COMMITTED, TRANSACTION_REPEATABLE_READ, etc. Default: none

🔤username
This property sets the default authentication username used when obtaining Connections from the underlying driver. Default: none

Missing Knobs
HikariCP has plenty of "knobs" to turn as you can see above, but comparatively less than some other pools. This is a design philosophy. The HikariCP design asthetic is Minimalism. In keeping with the simple is better or less is more design philosophy, some knobs and features are intentionally left out. Here are two, and the rationale.

Statement Cache
Most major database JDBC drivers already have a Statement cache that can be configured (Oracle, MySQL, PostgreSQL, Derby, etc). A statement cache in the pool would add unneeded weight and no additional functionality. It is simply unnecessary with modern database drivers to implement a cache at the pool level.

Log Statement Text / Slow Query Logging
Like Statement caching, most major database vendors support statement logging through properties of their own driver. This includes Oracle, MySQL, Derby, MSSQL, and others. Some even support slow query logging. We consider this a "development-time" feature. For those few databases that do not support it, jdbcdslog-exp is a good option. Great stuff during development and pre-Production.

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Initialization

You can use the HikariConfig class like so:

HikariConfig config = new HikariConfig();
config.setMaximumPoolSize(100);
config.setDataSourceClassName("com.mysql.jdbc.jdbc2.optional.MysqlDataSource");
config.addDataSourceProperty("serverName", "localhost");
config.addDataSourceProperty("port", "3306");
config.addDataSourceProperty("databaseName", "mydb");
config.addDataSourceProperty("user", "bart");
config.addDataSourceProperty("password", "51mp50n");

HikariDataSource ds = new HikariDataSource(config);

or property file based:

HikariConfig config = new HikariConfig("some/path/hikari.properties");
HikariDataSource ds = new HikariDataSource(config);

Example property file:

connectionTestQuery=SELECT 1
dataSourceClassName=org.postgresql.ds.PGSimpleDataSource
dataSource.user=test
dataSource.password=test
dataSource.databaseName=mydb
dataSource.serverName=localhost

or java.util.Properties based:

Properties props = new Properties();
props.setProperty("dataSourceClassName", "org.postgresql.ds.PGSimpleDataSource");
props.setProperty("dataSource.user", "test");
props.setProperty("dataSource.password", "test");
props.setProperty("dataSource.databaseName", "mydb");
props.setProperty("dataSource.logWriter", new PrintWriter(System.out));

HikariConfig config = new HikariConfig(props);
HikariDataSource ds = new HikariDataSource(config);

HikariConfig vs. HikariDataSource

Finally, you can skip the HikariConfig class altogether and configure the HikariDataSource directly:

HikariDataSource ds = new HikariDataSource();
ds.setMaximumPoolSize(15);
ds.setDataSourceClassName("com.mysql.jdbc.jdbc2.optional.MysqlDataSource");
ds.addDataSourceProperty("serverName", "localhost");
ds.addDataSourceProperty("databaseName", "mydb");
ds.addDataSourceProperty("user", "bart");
ds.addDataSourceProperty("password", "51mp50n");

The advantage of configuring via HikariConfig over HikariDataSource is that when using the HikariConfig we know at DataSource construction-time what the configuration is, so the pool can be initialized at that point. However, when using HikariDataSource alone, we don't know that you are done configuring the DataSource until getConnection() is called. In that case, getConnection() must perform an additional check to see if the pool has been initialized yet or not. The cost (albeit small) of this check is incurred on every invocation of getConnection() in that case. In summary, intialization by HikariConfig is ever so slightly more performant than initialization directly on the HikariDataSource -- not just at construction time but also at runtime.

Popular DataSource Class Names

We recommended using dataSourceClassName instead of driverClassName/jdbcUrl, as using the driver class requires HikariCP to wrap the driver with an internal DataSource class. Here is a list of JDBC DataSource classes for popular databases:

Database	Driver	DataSource class
Apache Derby	Derby	org.apache.derby.jdbc.ClientDataSource
H2	H2	org.h2.jdbcx.JdbcDataSource
HSQLDB	HSQLDB	org.hsqldb.jdbc.JDBCDataSource
MariaDB & MySQL	MariaDB	org.mariadb.jdbc.MySQLDataSource
MySQL	Connector/J	com.mysql.jdbc.jdbc2.optional.MysqlDataSource
MS SQL Server	Microsoft	com.microsoft.sqlserver.jdbc.SQLServerDataSource
Oracle	Oracle	oracle.jdbc.pool.OracleDataSource
PostgreSQL	pgjdbc-ng	com.impossibl.postgres.jdbc.PGDataSource
PostgreSQL	PostgreSQL	org.postgresql.ds.PGSimpleDataSource
SyBase	jConnect	com.sybase.jdbcx.SybDataSource

Play Framework Plugin

Github user autma has created a plugin for the Play framework. Thanks!

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Support ^💬

Google discussion group HikariCP here, growing FAQ.

 

Wiki

Don't forget the Wiki for additional information such as:

• FAQ
• Hibernate 4.x Configuration
• MySQL Configuration Tips
• etc.

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Requirements

⇒ Java 6 and above
⇒ Javassist 3.18.1+ library
⇒ slf4j library

Contributions

Please perform changes and submit pull requests from the dev branch instead of master. Please set your editor to use spaces instead of tabs, and adhere to the apparent style of the code you are editing. The dev branch is always more "current" than the master if you are looking to live life on the edge.