Fast, simple, reliable. HikariCP is a "zero-overhead" production ready JDBC connection pool. Coming in at roughly 70Kb, the library is very light. Read about how we do it here.
"Simplicity is prerequisite for reliability."
- Edsger Djikstra
Java 8 maven artifact:
<dependency>
<groupId>com.zaxxer</groupId>
<artifactId>HikariCP</artifactId>
<version>2.1.0</version>
<scope>compile</scope>
</dependency>Java 6 and Java 7 maven artifact:
<dependency>
<groupId>com.zaxxer</groupId>
<artifactId>HikariCP-java6</artifactId>
<version>2.1.0</version>
<scope>compile</scope>
</dependency>JMH Benchmarks
Microbenchmarks were created to isolate and measure the overhead of pools using the JMH microbenchmark framework developed by the Oracle JVM performance team. 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().
2 Java options: -server -XX:+AggressiveOpts -XX:+UseFastAccessorMethods -Xmx512m
User Testimonials
The guys over at Edulify were experiencing connection leaks and other issues using BoneCP in their Play Framework application. They created a HikariCP plugin for Play Framework to give HikariCP a try.
In their own words, "HikariCP is supposed to be the fastest connection pool in Java land. But we did not start to use it because of speed, but because of its reliability. Here is a cool graph that shows connections opened to PostgreSQL. As you can see, the pool is way more stable. Also it is keeping its size at the minimum since we deploy it."
Not all pools are created equal. Read our pool analysis here if you care to know the good, bad, and ugly.
AKA "What you probably didn't know about connection pool sizing". Read on to find out.
HikariCP comes with sane defaults that perform well in most deployments without additional tweaking.
📎 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
❎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
🔤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
🔤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
⌚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. 100ms is the minimum value. Default: 30000 (30 seconds)
⌚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)
⌚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)
⌚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. Lowest acceptable value for enabling leak
detection is 10000 (10 secs). Default: 0
❎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 minimumIdle is 0. 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
🔤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
🔤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
🔤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
➡️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
🔤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
🔤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
#️⃣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
#️⃣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
🔤username
This property sets the default authentication username used when obtaining Connections from
the underlying driver. Note that for DataSources this works in a very deterministic fashion by
calling DataSource.getConnection(*username*, password) on the underlying DataSource. However,
for Driver-based configurations, every driver is different. In the case of Driver-based, HikariCP
will use this username property to set a user property in the Properties passed to the
driver's DriverManager.getConnection(jdbcUrl, props) call. If this is not what you need,
skip this method entirely and call addDataSourceProperty("username", ...), for example.
Default: none
🔤password
This property sets the default authentication password used when obtaining Connections from
the underlying driver. Note that for DataSources this works in a very deterministic fashion by
calling DataSource.getConnection(username, *password*) on the underlying DataSource. However,
for Driver-based configurations, every driver is different. In the case of Driver-based, HikariCP
will use this password property to set a password property in the Properties passed to the
driver's DriverManager.getConnection(jdbcUrl, props) call. If this is not what you need,
skip this method entirely and call addDataSourceProperty("pass", ...), for example.
Default: none
🔤poolName
This property represents a user-defined name for the connection pool and appears mainly
in logging and JMX management consoles to identify pools and pool configurations. Default: auto-generated
❎registerMbeans
This property controls whether or not JMX Management Beans ("MBeans") are registered or not.
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
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.
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=localhostor 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);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.
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 |
| Firebird | Jaybird | org.firebirdsql.pool.FBSimpleDataSource |
| IBM DB2 | DB2 | com.ibm.db2.jcc.DB2SimpleDataSource |
| 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 |
A new plugin has come up for the the Play framework; play-hikaricp. If you're using the excellent Play framework, your application deserves HikariCP. Thanks Edulify Team!
A new Clojure wrapper has been created by tomekw and can be found here.
Google discussion group HikariCP here, growing FAQ.
Don't forget the Wiki for additional information such as:
⇒ Java 6 and above
⇒ Javassist 3.18.1+ library
⇒ slf4j library
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.