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<h1>
<div>c3p0 - JDBC3 Connection and Statement Pooling</div>
<div class="subtitle">version @c3p0.version@</div>
</h1>
<div class="top_boilerplate">
<p>by Steve Waldman <<a href="mailto:swaldman@mchange.com">swaldman@mchange.com</a>></p>
<p>© @c3p0.copyright.year@ Machinery For Change, Inc.</p>
<p><i>
This software is made available for use, modification, and redistribution,
under the terms of the
<a href="http://www.gnu.org/licenses/lgpl-2.1.html">Lesser GNU Public License, v.2.1 (LGPL)</a> or
the <a href="http://www.eclipse.org/legal/epl-v10.html">Eclipse Public License, v.1.0 (EPL)</a>,
at your option. You should have received copies of both licenses with this distribution.
</i></p>
<ul class="pointerlist">
<li>API docs for c3p0 are <a href="apidocs/index.html">here</a>.</li>
<li>Looking for the definition of <a href="#configuration_properties">configuration properties</a>?</li>
<li>Looking for advice in <a href="#hibernate-specific">using c3p0 with hibernate</a>?</li>
</ul>
<ul class="pointerlist">
<li>Download the latest version from <a href="http://sourceforge.net/projects/c3p0/">c3p0's site on SourceForge</a></li>
<li>Follow or fork <a href="https://github.com/swaldman/c3p0">c3p0 on GitHub</a>.</li>
<li>Follow <a href="https://twitter.com/c3p0_jdbc">@c3p0_jdbc</a> on Twitter.</li>
</ul>
<p><b>Note:</b> Coordinates of this version on the Maven central repository: <tt>[groupId: com.mchange, artifactId: c3p0, version: @c3p0.version@]</tt></p>
</div>
<hr/>
<h2><a name="contents">Contents</a></h2>
<ol class="contents">
<li><a href="#contents">Contents</a></li>
<li><a href="#quickstart">Quickstart</a></li>
<li><a href="#what_is">What is c3p0?</a></li>
<li><a href="#prerequisites">Prerequisites</a></li>
<li><a href="#installation">Installation</a></li>
<li>
<a href="#using_c3p0">Using c3p0</a>
<ol class="contents">
<li><a href="#using_combopooleddatasource">Using ComboPooledDataSource</a></li>
<li><a href="#using_datasources_factory">Using the DataSouces factory class</a></li>
<ul class="box">
<li><a href="#forceOverrideBox">Box: Overriding authentication information (from non-c3p0 DataSources)</a></li>
</ul>
<li><a href="#querying">Querying Pool Status</a></li>
<ul class="box">
<li><a href="#using_c3p0_registry_box">Box: Using C3P0Registry to find a reference to a DataSource</a></li>
</ul>
<li><a href="#cleaning">Cleaning Up Pool Resources</a></li>
<li><a href="#build_your_own">Advanced: Building Your Own PoolBackedDataSource</a></li>
<li><a href="#raw_connection_ops">Advanced: Raw Connection and Statement Operations</a></li>
</ol>
</li>
<li>
<a href="#configuration">Configuration</a>
<ol class="contents">
<li><a href="#configuration_introduction">Introduction</a></li>
<li><a href="#basic_pool_configuration">Basic Pool Configuration</a></li>
<li><a href="#managing_pool_size">Managing Pool Size and Connection Age</a></li>
<li><a href="#configuring_connection_testing">Configuring Connection Testing</a></li>
<li><a href="#configuring_statement_pooling">Configuring Statement Pooling</a></li>
<li><a href="#configuring_recovery">Configuring Recovery From Database Outages</a></li>
<li><a href="#connection_customizers">Managing Connection Lifecycles with Connection Customizers</a></li>
<li><a href="#configuring_unresolved">Configuring Unresolved Transaction Handling</a></li>
<li><a href="#configuring_to_debug_and_workaround_broken_clients">Configuring to Debug and Workaround Broken Client Applications</a></li>
<li><a href="#other_ds_configuration">Other DataSource Configuration</a></li>
<li><a href="#jmx_configuration_and_management">Configuring and Managing c3p0 via JMX</a></li>
<li><a href="#configuring_logging">Configuring Logging</a></li>
</ol>
</li>
<li><a href="#performance">Performance</a></li>
<li><a href="#known_shortcomings">Known shortcomings</a></li>
<li><a href="#feedback_and_support">Feedback and support</a></li>
<li><a href="#configuration_properties">Appendix A: Configuration Properties</a></li>
<li><a href="#configuration_files">Appendix B: Configuation Files, etc.</a></li>
<ol class="contents">
<li><a href="#c3p0_properties">Overriding c3p0 defaults with a c3p0.properties file</a></li>
<li><a href="#system_properties">Overriding c3p0 defaults with System properties</a></li>
<li><a href="#c3p0-config.xml">Named and Per-User configuration: Overriding c3p0 defaults via c3p0-config.xml</a></li>
<li><a href="#configuration_precedence">Precedence of Configuration Settings</a></li>
</ol>
<li><a href="#hibernate-specific">Appendix C: Hibernate-specific notes</a></li>
<li><a href="#tomcat-specific">Appendix D: Configuring c3p0 pooled DataSources for Apache Tomcat</a></li>
<li><a href="#jboss-specific">Appendix E: JBoss-specific notes</a></li>
<li><a href="#oracle-specific">Appendix F: Oracle-specific API: createTemporaryBLOB() and createTemporaryCLOB()</a></li>
</ol>
(See also the API Documentation <a href="apidocs/index.html">here</a>)
<hr/>
<h2><a name="quickstart">Quickstart</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
c3p0 was designed to be butt-simple to use. Just put
the files <tt>lib/c3p0-@c3p0.version@.jar</tt> and <tt>lib/mchange-commons-java-@mchange-commons-java.version@.jar</tt> in your application's
effective <tt>CLASSPATH</tt>, then make a DataSource like this:
</p>
<div class="example">
import com.mchange.v2.c3p0.*;
...
ComboPooledDataSource cpds = new ComboPooledDataSource();
cpds.setDriverClass( "org.postgresql.Driver" ); //loads the jdbc driver
cpds.setJdbcUrl( "jdbc:postgresql://localhost/testdb" );
cpds.setUser("dbuser");
cpds.setPassword("dbpassword");
</div>
<p>
<b>[Optional]</b> If you want to turn on PreparedStatement pooling, you must also set <tt>maxStatements</tt>
and/or <tt>maxStatementsPerConnection</tt> (both default to 0):
</p>
<div class="example">
cpds.setMaxStatements( 180 );
</div>
<p>
Do whatever you want with your DataSource, which will be backed
by a Connection pool set up with default parameters. You
can bind the DataSource to a JNDI name service, or use it
directly, as you prefer.
</p>
<p>
When you are done, you can clean up the DataSource you've created
like this:
</p>
<div class="example">
DataSources.destroy( cpds );
</div>
<p>
That's it! The rest is detail.
</p>
</div>
<h2><a name="basics">What is c3p0?</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
c3p0 is an easy-to-use library for making traditional JDBC drivers
"enterprise-ready" by augmenting them with functionality defined by
the jdbc3 spec and the optional extensions to jdbc2. In particular,
c3p0 provides several useful services:
</p>
<ul>
<li>
Classes which adapt traditional DriverManager-based JDBC
drivers to the new <tt>javax.sql.DataSource</tt> scheme for acquiring
database Connections.
</li>
<li>
Transparent pooling of Connection and PreparedStatements
behind DataSources which can "wrap" around traditional
drivers or arbitrary unpooled DataSources.
</li>
</ul>
<p>
The library tries hard to get the details right:
</p>
<ul>
<li>
c3p0 DataSources are both <tt>Referenceable</tt> and <tt>Serializable</tt>, and are thus
suitable for binding to a wide-variety of JNDI-based naming services.
</li>
<li>
Statement and ResultSets are carefully cleaned up when pooled
Connections and Statements are checked in, to prevent resource-
exhaustion when clients use the lazy but common resource-management
strategy of only cleaning up their Connections....
</li>
<li>
The library adopts the approach
defined by the JDBC 2 and 3 specification (even where these
conflict with the library author's preferences). DataSources
are written in the JavaBean style, offering all the required and
most of the optional properties (as well as some non-standard ones),
and no-arg constructors. All JDBC-defined internal interfaces are
implemented (ConnectionPoolDataSource, PooledConnection,
ConnectionEvent-generating Connections, etc.)
You can mix c3p0 classes with compliant third-party implementations
(although not all c3p0 features will work with external implementations).
</li>
</ul>
<p>
c3p0 hopes to provide DataSource implementations more than suitable for
use by high-volume "J2EE enterprise applications". Please provide feedback, bug-fixes, etc.!
</p>
</div>
<h2><a name="prerequisites">Prerequisites</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
c3p0 requires a level 1.3.x or above Java Runtime Environment, and
the JDBC 2.x or above javax.sql libraries. c3p0 works fine under
Java 1.4.x and 1.5.x as well.
</p>
</div>
<h2><a name="installation">Installation</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
Put the file <tt>lib/c3p0-@c3p0.version@.jar</tt>
somewhere in your CLASSPATH (or any other place where your application's
classloader will find it). That's it!
</p>
</div>
<h2><a name="using_c3p0">Using c3p0</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
From a users' perspective, c3p0 simply provides standard jdbc2 DataSource
objects. When creating these DataSources, users can control pooling-related,
naming-related, and other properties (See <a href="#configuration_properties">Appendix A</a>). All pooling is entirely
transparent to users once a DataSource has been created.
</p>
<p>
There are three ways of acquiring c3p0 pool-backed DataSources: 1) directly instantiate and configure a
<a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>ComboPooledDataSource</tt></a> bean;
2) use the DataSources factory class; or 3) "build your own" pool-backed
DataSource by directly instantiating <tt>PoolBackedDataSource</tt> and setting its <tt>ConectionPoolDataSource</tt>. Most
users will probably find instantiating <a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>ComboPooledDataSource</tt></a>
to be the most convenient approach. Once instantiated,
c3p0 DataSources can be bound to nearly any JNDI-compliant name service.
</p>
<p>
Regardless of how you create your DataSource, c3p0 will use defaults for any configuration parameters that
you do not specify programmatically. c3p0 has built-in, hard-coded defaults, but you can override these by creating
a file called <tt>c3p0.properties</tt> and storing it as a top-level resource in the same <tt>CLASSPATH</tt> (or ClassLoader)
that loads c3p0's jar file. As of c3p0-0.9.1, you can also supply a file called <tt>c3p0-config.xml</tt> for more advanced
configuration. See <a href="#configuration">Configuration</a> below.
</p>
<h3>
<a name="using_combopooleddatasource">Instantiating and Configuring a ComboPooledDataSource</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
Perhaps the most straightforward way to create a c3p0 pooling DataSource is to instantiate an instance of
<a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>com.mchange.v2.c3p0.ComboPooledDataSource</tt></a>.
This is a JavaBean-style class with a public, no-arg constructor,
but before you use the DataSource, you'll have to be sure to set at least the property <tt>jdbcUrl</tt>. You may also
want to set <tt>user</tt> and <tt>password</tt>, and if you have not externally preloaded the old-style JDBC driver you'll
use you should set the <tt>driverClass</tt>.
</p>
<div class="example">
ComboPooledDataSource cpds = new ComboPooledDataSource();
cpds.setDriverClass( "org.postgresql.Driver" ); //loads the jdbc driver
cpds.setJdbcUrl( "jdbc:postgresql://localhost/testdb" );
cpds.setUser("swaldman");
cpds.setPassword("test-password");
// the settings below are optional -- c3p0 can work with defaults
cpds.setMinPoolSize(5);
cpds.setAcquireIncrement(5);
cpds.setMaxPoolSize(20);
// The DataSource cpds is now a fully configured and usable pooled DataSource
...
</div>
<p>
The defaults of any c3p0 DataSource are determined by configuration you supply, or
else revert to hard-coded defaults [see <a href="#configuration_properties">configuration properties</a>].
c3p0-0.9.1 and above supports <a href="#c3p0-config.xml">multiple, named configurations</a>.
If you wish to use a named configuration, construct your
<a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>com.mchange.v2.c3p0.ComboPooledDataSource</tt></a>
with the configuration name as a constructor agument:
</p>
<div class="example">
ComboPooledDataSource cpds = new ComboPooledDataSource("intergalactoApp");
</div>
<p>
Of course, you can still override any configuration properties programmatically, as above.
</p>
<h3>
<a name="using_datasources_factory">Using the DataSources factory class</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
Alternatively, you can use the static factory class
<a href="apidocs/com/mchange/v2/c3p0/DataSources.html"><tt>com.mchange.v2.c3p0.DataSources</tt></a> to build unpooled DataSources
from traditional JDBC drivers, and to build pooled DataSources from unpooled DataSources:
</p>
<div class="example">
DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb",
"swaldman",
"test-password");
DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled );
// The DataSource ds_pooled is now a fully configured and usable pooled DataSource.
// The DataSource is using a default pool configuration, and Postgres' JDBC driver
// is presumed to have already been loaded via the jdbc.drivers system property or an
// explicit call to Class.forName("org.postgresql.Driver") elsewhere.
...
</div>
<p>
If you use the <a href="apidocs/com/mchange/v2/c3p0/DataSources.html">DataSources</a>
factory class, and you want to programmatically override default configuration
parameters, you can supply a map of override properties:
</p>
<div class="example">
DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb",
"swaldman",
"test-password");
Map overrides = new HashMap();
overrides.put("maxStatements", "200"); //Stringified property values work
overrides.put("maxPoolSize", new Integer(50)); //"boxed primitives" also work
// create the PooledDataSource using the default configuration and our overrides
ds_pooled = DataSources.pooledDataSource( ds_unpooled, overrides );
// The DataSource ds_pooled is now a fully configured and usable pooled DataSource,
// with Statement caching enabled for a maximum of up to 200 statements and a maximum
// of 50 Connections.
...
</div>
<p>
If you are using <a href="#c3p0-config.xml">named configurations</a>, you can specify the configuration
that defines the default configuration for your DataSource:
</p>
<div class="example">
// create the PooledDataSource using the a named configuration and specified overrides
ds_pooled = DataSources.pooledDataSource( ds_unpooled, "intergalactoAppConfig", overrides );
</div>
<p><a id="showDataSourcesWithPoolConfig"
style="display: block"
href="#"
onClick="return toggleDisplay('showDataSourcesWithPoolConfig', 'DataSourcesWithPoolConfig');"
>Show deprecated PoolConfig approach...</a></p>
<div class="deprecated" style="display: none" id="DataSourcesWithPoolConfig">
<h5>Deprecated! Programmatic configuration via PoolConfig</h5>
<p>
If you use the <a href="apidocs/com/mchange/v2/c3p0/DataSources.html">DataSources</a>
factory class, and you want to programmatically override default configuration
parameters, make use of the <a href="apidocs/com/mchange/v2/c3p0/PoolConfig.html"><tt>PoolConfig</tt></a> class:
</p>
<div class="example">
DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb",
"swaldman",
"test-password");
PoolConfig pc = new PoolConfig();
pc.setMaxStatements(200); //turn on Statement pooling
// pass our overriding PoolConfig to the DataSources.pooledDataSource() factory method.
ds_pooled = DataSources.pooledDataSource( ds_unpooled, pc );
// The DataSource ds_pooled is now a fully configured and usable pooled DataSource,
// with Statement caching enabled for a maximum of up to 200 statements.
...
</div>
<a id="hideDataSourcesWithPoolConfig"
href="#"
onClick="return toggleDisplay('showDataSourcesWithPoolConfig', 'DataSourcesWithPoolConfig');"
>Hide deprecated PoolConfig approach</a>
</div>
<div class="boxed">
<a name="forceOverrideBox" />
<h4>RARE: Forcing authentication information, regardless of (mis)configuration of the underlying (unpooled) DataSource</h4>
<p>
You can wrap any DataSouce using <tt>DataSource.pooledDataSource( ... )</tt>, usually with no
problem whatsoever. DataSources are supposed to indicate the username and password associated
by default with Connections via standard properties <tt>user</tt> and <tt>password</tt>.
Some DataSource implementations do not offer these properties. Usually this is not at all
a problem. <tt>c3p0</tt> works around this
by acquiring "default" Connections from the DataSource if it can't find default authentication
information, and a client has not specified the authentification information via
<tt>getConnection( user, password )</tt>.
</p>
<p>
However, in rare circumstances, non-c3p0 unpooled DataSources provide a <tt>user</tt> property,
but not a password property, or you have access to a DataSource that you wish to wrap behind a pool,
but you wish to override its build-in authentification defaults without actually modifying the <tt>user</tt>
or <tt>password</tt> properties.
</p>
<p>
<tt>c3p0</tt> provides configuation properties <tt>overrideDefaultUser</tt> and <tt>overrideDefaultPassword</tt>.
If you set these properties, programmatically as above, or via any of c3p0's <a href="#configuration">configuration mechanisms</a>,
<tt>c3p0</tt> PooledDataSources will ignore the user and password property associated with the underlying DataSource,
and use the specified overrides instead.
</p>
</div>
<h3>
<a name="querying">Querying a PooledDataSource's current status</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 DataSources backed by a pool, which include implementations of
<a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>ComboPooledDataSource</tt></a> and
the objects returned by <tt><a href="apidocs/com/mchange/v2/c3p0/DataSources.html">DataSources</a>.pooledDataSource( ... )</tt>,
all implement the interface
<a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html"><tt>com.mchange.v2.c3p0.PooledDataSource</tt></a>,
which makes available a number of methods for querying the status of
DataSource Connection pools. Below is sample code that queries a DataSource for its
status:
</p>
<div class="example">
// fetch a JNDI-bound DataSource
InitialContext ictx = new InitialContext();
DataSource ds = (DataSource) ictx.lookup( "java:comp/env/jdbc/myDataSource" );
// make sure it's a c3p0 PooledDataSource
if ( ds instanceof PooledDataSource)
{
PooledDataSource pds = (PooledDataSource) ds;
System.err.println("num_connections: " + pds.getNumConnectionsDefaultUser());
System.err.println("num_busy_connections: " + pds.getNumBusyConnectionsDefaultUser());
System.err.println("num_idle_connections: " + pds.getNumIdleConnectionsDefaultUser());
System.err.println();
}
else
System.err.println("Not a c3p0 PooledDataSource!");
</div>
<p>
The status querying methods all come in three overloaded forms, such as:
</p>
<ul>
<li><tt>public int getNumConnectionsDefaultUser()</tt></li>
<li><tt>public int getNumConnections(String username, String password)</tt></li>
<li><tt>public int getNumConnectionsAllUsers()</tt></li>
</ul>
<p>
c3p0 maintains separate pools for Connections with distinct
authentications. The various methods let you query the status of pools individually,
or aggregate statistics for all authentifications for which your DataSource is maintaining
pools. <i>Note that pool configuration parmeters such as <tt>maxPoolSize</tt> are enforced
on a per-authentification basis!</i> For example, if you have set <tt>maxPoolSize</tt> to
20, and if the DataSource is managing connections under two username-password pairs [the
default, and one other pair established via a call to <tt>getConnection(user, password)</tt>,
you should expect to see as many as 40 Connections from <tt>getNumConnectionsAllUsers()</tt>.
</p>
<p>
<i>
Most applications only acquire default-authenticated Connections from DataSources, and
can typically just use the <tt>getXXXDefaultUser()</tt> to gather Connection statistics.
</i>
</p>
<p>
As well as Connection pool realted statistics, you can retrieve status information about each
DataSource's Thread pool.
Please see <a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html"><tt>PooledDataSource</tt>
for a complete list of available operations.</a>
</p>
<div class="boxed">
<a name="using_c3p0_registry_box" />
<h4>Using C3P0Registry to get a reference to a DataSource</h4>
<p>
If it's inconvenient or impossible to get a reference to your DataSource via JNDI or some other means,
you can find all live c3p0 DataSources using the
<a href="apidocs/com/mchange/v2/c3p0/C3P0Registry.html"><tt>C3P0Registry</tt></a> class, which includes
three static methods to help you out:
</p>
<ul>
<li><tt>public static Set getPooledDataSources()</tt></li>
<li><tt>public static Set pooledDataSourcesByName( String dataSourceName )</tt></li>
<li><tt>public static <a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html">PooledDataSource</a>
pooledDataSourceByName( String dataSourceName )</tt></li>
</ul>
<p>
The first method will hand you the Set of all live c3p0
<a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html">PooledDataSources</a>. If you are sure
your application only makes one <a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html">PooledDataSources</a>,
or you can distinguish between the DataSources by their configuration properties (inspected via "getters"), the
first method may be sufficient. Because this will not always be the case, c3p0
<a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html">PooledDataSources</a> have a special property called
<tt>dataSourceName</tt>. You can set the <tt>dataSourceName</tt> property directly when you construct your
DataSource, or dataSourceName can be set like any other property in a named or the default config.
Otherwise, <tt>dataSourceName</tt> will default to either 1) the name of your DataSource's configuration, if
you constructed it with a <a href="#c3p0-config.xml">named configuration</a>; or 2) a unique (but unpredicatble)
name if you are using the default configuration.
</p>
<p>
There is no guarantee that a <tt>dataSourceName</tt> will be unique. For example, if two c3p0 DataSources share
the same <a href="#c3p0-config.xml">named configuration</a>, and you have not set the <tt>dataSourceName</tt> programmatically, the two
data sources will both share the name of the configuration. To get all of the DataSources with a particular
<tt>dataSourceName</tt>, use <tt>pooledDataSourcesByName( ... )</tt>. If you've ensured that your DataSource's
name is unique (as you will generally want to do, if you intend to use
<a href="apidocs/com/mchange/v2/c3p0/C3P0Registry.html"><tt>C3P0Registry</tt></a> to find your DataSources),
you can use the convenience method <tt>pooledDataSourceByName( ... )</tt>, which will return your DataSource
directly, or <tt>null</tt> if no DataSource with that name is available. If you use <tt>pooledDataSourceByName( ... )</tt>
and more than one DataSource shares the name supplied, which one it will return is undefined.
</p>
</div>
<h3>
<a name="cleaning">Cleaning up after c3p0 PooledDataSources</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
The easy way to clean up after c3p0-created DataSources is to use the static destroy method
defined by the class <a href="apidocs/com/mchange/v2/c3p0/DataSources.html">DataSources</a>. Only
<a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html"><tt>PooledDataSource</tt></a>s
need to be cleaned up, but
<a href="apidocs/com/mchange/v2/c3p0/DataSources.html">DataSources</a>.destroy( ... ) does no harm if it is called on an unpooled or non-c3p0
DataSource.
</p>
<div class="example">
DataSource ds_pooled = null;
try
{
DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:postgresql://localhost/testdb",
"swaldman",
"test-password");
ds_pooled = DataSources.pooledDataSource( ds_unpooled );
// do all kinds of stuff with that sweet pooled DataSource...
}
finally
{
DataSources.destroy( ds_pooled );
}
</div>
<p>
Alternatively, c3p0's <a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html"><tt>PooledDataSource</tt></a>
interface contains a <tt>close()</tt> method
that you can call when you know you are finished with a DataSource. So, you can cast a c3p0
derived DataSource to a <tt>PooledDataSource</tt> and close it:
</p>
<div class="example">
static void cleanup(DataSource ds) throws SQLException
{
// make sure it's a c3p0 PooledDataSource
if ( ds instanceof PooledDataSource)
{
PooledDataSource pds = (PooledDataSource) ds;
pds.close();
}
else
System.err.println("Not a c3p0 PooledDataSource!");
}
</div>
<p>
Unreferenced instances of <a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html"><tt>PooledDataSource</tt></a>
that are not <tt>close()</tt>ed by clients
<tt>close()</tt> themselves prior to garbage collection in their <tt>finalize()</tt> methods.
As always, finalization should be considered
a backstop and not a prompt or sure approach to resource cleanup.
</p>
<h3>
<a name="build_your_own">Advanced: Building your own PoolBackedDataSource</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
There is little reason for most programmers to do this, but you can build a PooledDataSource in a
step-by-step way by instantiating and configuring an unpooled
<a href="apidocs/com/mchange/v2/c3p0/DriverManagerDataSource.html"><tt>DriverManagerDataSource</tt></a>, instantiating a
<a href="apidocs/com/mchange/v2/c3p0/WrapperConnectionPoolDataSource.html"><tt>WrapperConnectionPoolDataSource</tt></a>
and setting the unpooled DataSource as its <tt>nestedDataSource</tt> property,
and then using that to set the <tt>connectionPoolDataSource</tt> property of a new
<a href="apidocs/com/mchange/v2/c3p0/PoolBackedDataSource.html"><tt>PoolBackedDataSource</tt></a>.
</p>
<p>
This sequence of events is primarily interesting if your driver offers an implementation of ConnectionPoolDataSource, and you'd
like c3p0 to use that. Rather than using c3p0's
<a href="apidocs/com/mchange/v2/c3p0/WrapperConnectionPoolDataSource.html"><tt>WrapperConnectionPoolDataSource</tt></a>,
you can create a <a href="apidocs/com/mchange/v2/c3p0/PoolBackedDataSource.html"><tt>PoolBackedDataSource</tt></a>
and set its <tt>connectionPoolDataSource</tt> property. Statement pooling,
<a href="apidocs/com/mchange/v2/c3p0/ConnectionCustomizer.html"><tt>ConnectionCustomizers</tt></a>, and many c3p0-specific properties
are unsupported with third party implementations of <tt>ConnectionPoolDataSource</tt>. (Third-party <tt>DataSource</tt> implementations
can be substituted for c3p0's
<a href="apidocs/com/mchange/v2/c3p0/DriverManagerDataSource.html"><tt>DriverManagerDataSource</tt></a> with no significant loss of
functionality.)
</p>
<h3>
<a name="raw_connection_ops">Advanced: Raw Connection and Statement Operations</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
JDBC drivers sometimes define vendor-specific, non-standard API on Connection and Statement implementations. C3P0 wraps
these Objects behind a proxies, so you cannot cast C3P0-returned Connections or Statements to the vendor-specific implementation
classes. C3P0 does not provide any means of accessing the raw Connections and Statements directly, because C3P0 needs to keep
track of Statements and ResultSets created in order to prevent resource leaks and pool
corruption.
</p>
<p>
C3P0 does provide an API that allows you to invoke non-standard methods reflectively on an underlying
Connection. To use it, first cast the returned Connection to a
<a href="apidocs/com/mchange/v2/c3p0/C3P0ProxyConnection.html"><tt>C3P0ProxyConnection</tt></a>. Then call
the method <tt>rawConnectionOperation</tt>, supplying the <tt>java.lang.reflect.Method</tt> object for
the non-standard method you wish to call as an argument. The <tt>Method</tt> you supply will be invoked
on the target you provide on the second argument (null for static methods), and using the arguments you
supply in the third argument to that function. For the target, and for any of the method arguments, you
can supply the special token <tt>C3P0ProxyConnection.RAW_CONNECTION</tt>, which will be replaced with
the underlying vendor-specific Connection object before the <tt>Method</tt> is invoked.
</p>
<p>
<a href="apidocs/com/mchange/v2/c3p0/C3P0ProxyStatement.html"><tt>C3P0ProxyStatement</tt></a> offers
an exactly analogous API.
</p>
<p>
Any Statements (including Prepared and CallableStatements) and ResultSets returned by raw operations
will be c3p0-managed, and will be properly cleaned-up on <tt>close()</tt> of the parent proxy Connection.
Users must take care to clean up any non-standard resources returned by a vendor-specific method.
</p>
<p>
Here's an example of using Oracle-specific API to call a static method on a raw Connection:
</p>
<div class="example">
C3P0ProxyConnection castCon = (C3P0ProxyConnection) c3p0DataSource.getConnection();
Method m = CLOB.class.getMethod("createTemporary", new Class[]{Connection.class, boolean.class, int.class});
Object[] args = new Object[] {C3P0ProxyConnection.RAW_CONNECTION, Boolean.valueOf( true ), new Integer( 10 )};
CLOB oracleCLOB = (CLOB) castCon.rawConnectionOperation(m, null, args);
</div>
<p>
<i>Note: C3P0 now includes special support for some Oracle-specific methods.
See <a href="#oracle-specific">Appendix F</a>.
</i>
</p>
<h2><a name="configuration">Configuration</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<h3>
<a name="programmatic_configuration"></a><a name="configuration_introduction">Introduction</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
While c3p0 does not <i>require</i> very much configuration, it is very tweakable. Most of the interesting
knobs and dials are represented as JavaBean properties. Following JavaBean conventions, we note that
if an Object has a property of type <tt>T</tt> called <tt>foo</tt>, it will have methods that look
like...
<blockquote><tt>
public T getFoo();<br/>
public void setFoo(T foo);
</tt></blockquote>
...or both, depending upon whether the property is read-only, write-only, or read-writable.
</p>
<p>
There are several ways to modify c3p0 properties:
You can directly alter the property values associated with a particular DataSource in your code,
or you can configure c3p0 externally,
via a <a href="#c3p0_properties">simple Java properties file</a>,
via an <a href="#c3p0-config.xml">XML configuration file</a>, or
via <a href="#system_properties">System properties</a>. Configuration files
are normally looked up under standard names (<tt>c3p0.properties</tt> or <tt>c3p0-config.xml</tt>)
at the top level of an application's classpath, but the XML configuration can be placed
anywhere in an application's file system or classpath, if the system property <a href="#locating_configuration_information"><tt>com.mchange.v2.c3p0.cfg.xml</tt></a> is set.
</p>
<p>
DataSources are usually configured before they are used, either
during or immediately following their construction. c3p0 does
support property modifications midstream, however.
</p>
<p>
If you obtain a DataSource by instantiating a
<a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>ComboPooledDataSource</tt></a>,
configure it by simply calling appropriate setter methods offered by that class
before attempting a call to <tt>getConnection()</tt>. See the example above.
</p>
<p>
If you obtain a DataSource by using factory methods of
the utility class <a href="apidocs/com/mchange/v2/c3p0/DataSources.html"><tt>com.mchange.v2.c3p0.DataSources</tt></a>,
and wish to use a non-default configuration, you can supply a Map of property names (beginning with lower-case letters)
to property values (either as Strings or "boxed" Java primitives like Integer or Boolean).
</p>
<p>
All tweakable properties are documented for reference
in <a href="#configuration_properties">Appendix A</a>. The most basic and important c3p0 configuration
topics are discussed below.
</p>
<h3>
<a name="basic_pool_configuration">Basic Pool Configuration</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 Connection pools are very easy to configure via the following basic parameters:
</p>
<ul>
<li><a class="cfg_param" href="#acquireIncrement">acquireIncrement</a></li>
<li><a class="cfg_param" href="#initialPoolSize">initialPoolSize</a></li>
<li><a class="cfg_param" href="#maxPoolSize">maxPoolSize</a></li>
<li><a class="cfg_param" href="#maxIdleTime">maxIdleTime</a></li>
<li><a class="cfg_param" href="#minPoolSize">minPoolSize</a></li>
</ul>
<p>
<tt>initialPoolSize</tt>, <tt>minPoolSize</tt>, <tt>maxPoolSize</tt>
define the number of Connections that will be pooled. Please ensure that
<tt>minPoolSize <= maxPoolSize</tt>. Unreasonable values of <tt>initialPoolSize</tt> will
be ignored, and <tt>minPoolSize</tt> will be used instead.
</p>
<p>
Within the range between <tt>minPoolSize</tt> and <tt>maxPoolSize</tt>, the number of Connections in
a pool varies according to usage patterns. The number of Connections increases whenever a Connection
is requested by a user, no Connections are available, and the pool has not yet reached <tt>maxPoolSize</tt>
in the number of Connections managed. Since Connection acquisition is very slow, it is almost always useful to
increase the number of Connections eagerly, in batches, rather than forcing each client to wait for a new
Connection to provoke a single acquisition when the load is increasing. <tt>acquireIncrement</tt> determines
how many Connections a c3p0 pool will attempt to acquire when the pool has run out of Connections. (Regardless
of <tt>acquireIncrement</tt>, the pool will never allow <tt>maxPoolSize</tt> to be exceeded.)
</p>
<p>
The number of Connections in a pool decreases whenever a pool tests a Connection and finds it to be broken (see
<a href="#configuring_connection_testing">Configuring Connection Testing</a> below), or when a Connection is expired
by the pool after sitting idle for a period of time, or for being too old (See <a href="#managing_pool_size">Managing Pool Size and Connection Age</a>.)
</p>
<h3>
<a name="managing_pool_size">Managing Pool Size and Connection Age</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
Different applications have different needs with regard to trade-offs between performance, footprint, and reliability. C3P0
offers a wide variety of options for controlling how quickly pools that have grown large under load revert to <tt>minPoolSize</tt>,
and whether "old" Connections in the pool should be proactively replaced to maintain their reliablity.
</p>
<ul>
<li><a class="cfg_param" href="#maxConnectionAge">maxConnectionAge</a></li>
<li><a class="cfg_param" href="#maxIdleTime">maxIdleTime</a></li>
<li><a class="cfg_param" href="#maxIdleTimeExcessConnections">maxIdleTimeExcessConnections</a></li>
</ul>
<p>
By default, pools will never expire Connections. If you wish
Connections to be expired over time in order to maintain "freshness",
set <tt>maxIdleTime</tt> and/or <tt>maxConnectionAge</tt>. <tt>maxIdleTime</tt> defines how many seconds a
Connection should be permitted to go unused before being culled from the pool. <tt>maxConnectionAge</tt>
forces the pool to cull any Connections that were acquired from the database more than the set number of
seconds in the past.
</p>
<p>
<tt>maxIdleTimeExcessConnections</tt> is about minimizing the number of Connections held by c3p0 pools
when the pool is not under load. By default, c3p0 pools grow under load, but only shrink if Connections
fail a Connection test or are expired away via the parameters described above. Some users want their
pools to quickly release unnecessary Connections after a spike in usage that forces a large pool size.
You can achieve this by setting <tt>maxIdleTimeExcessConnections</tt> to a value much shorter than
<tt>maxIdleTime</tt>, forcing Connections beyond your set minimum size to be released if they sit idle
for more than a short period of time.
</p>
<p>
Some general advice about all of these timeout parameters: Slow down! The point of Connection pooling is to
bear the cost of acquiring a Connection only once, and then to reuse the Connection many, many times.
Most databases support Connections that remain open for hours at a time. There's no need to churn through
all your Connections every few seconds or minutes. Setting <tt>maxConnectionAge</tt> or <tt>maxIdleTime</tt> to 1800 (30 minutes)
is quite aggressive. For most databases, several hours may be more appropriate. You can ensure the reliability
of your Connections by testing them, rather than by tossing them. (see
<a href="#configuring_connection_testing">Configuring Connection Testing</a>.) The only one of these parameters
that should generally be set to a few minutes or less is <tt>maxIdleTimeExcessConnections</tt>.
</p>
<h3>
<a name="configuring_connection_testing">Configuring Connection Testing</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 can be configured to test the Connections that it pools in a variety of ways, to
minimize the likelihood that your application will see broken or "stale" Connections.
Pooled Connections can go bad for a variety of reasons -- some JDBC drivers intentionally
"time-out" long-lasting database Connections; back-end databases or networks sometimes go down
"stranding" pooled Connections; and Connections can simply become corrupted over time and use due
to resource leaks, driver bugs, or other causes.
</p>
<p>
c3p0 provides users a great deal of flexibility in testing Connections, via the following
configuration parameters:
</p>
<ul>
<li><a class="cfg_param" href="#automaticTestTable">automaticTestTable</a></li>
<li><a class="cfg_param" href="#connectionTesterClassName">connectionTesterClassName</a></li>
<li><a class="cfg_param" href="#idleConnectionTestPeriod">idleConnectionTestPeriod</a></li>
<li><a class="cfg_param" href="#preferredTestQuery">preferredTestQuery</a></li>
<li><a class="cfg_param" href="#testConnectionOnCheckin">testConnectionOnCheckin</a></li>
<li><a class="cfg_param" href="#testConnectionOnCheckout">testConnectionOnCheckout</a></li>
</ul>
<p>
<tt>idleConnectionTestPeriod</tt>, <tt>testConnectionOnCheckout</tt>, and
<tt>testConnectionOnCheckin</tt> control <u>when</u> Connections will be tested.
<tt>automaticTestTable</tt>, <tt>connectionTesterClassName</tt>, and <tt>preferredTestQuery</tt> control <u>how</u> they will be tested.
</p>
<p>
When configuring
Connection testing, first try to minimize the cost of each test. By default, Connections are tested
by calling the <tt>getTables()</tt> method on a Connection's associated <tt>DatabaseMetaData</tt>
object. This has the advantage of working with any database, and regardless of the database schema. However, empirically
a <tt>DatabaseMetaData.getTables()</tt> call is often much slower than a simple database query.
</p>
<p>
The most convenient way to speed up Connection testing is to define the parameter <tt>automaticTestTable</tt>. Using the name
you provide, c3p0 will create an empty table, and make a simple query against it to test the database. Alternatively, if your
database schema
is fixed prior to your application's use of the database, you can simply define a test query with the <tt>preferredTestQuery</tt>
parameter. Be careful, however. Setting <tt>preferredTestQuery</tt> will lead to errors as Connection tests fail
if the query target table does not exist in your database table <i>prior to initialization of your DataSource</i>.
</p>
<p>
Advanced users may define any kind of Connection testing they wish, by implementing a
<a href="apidocs/com/mchange/v2/c3p0/ConnectionTester.html">ConnectionTester</a> and supplying the
fully qualified name of the class as <tt>connectionTesterClassName</tt>. If you'd like your custom ConnectionTesters
to honor and support the <tt>preferredTestQuery</tt> and <tt>automaticTestTable</tt> parameters, implement
<a href="apidocs/com/mchange/v2/c3p0/UnifiedConnectionTester.html">UnifiedConnectionTester</a>, most conveniently by extending
<a href="apidocs/com/mchange/v2/c3p0/AbstractConnectionTester.html">AbstractConnectionTester</a>. See the <a href="apidocs/index.html">api docs</a>
for more information.
</p>
<p>
The most reliable time to test Connections is on check-out. But this is also the most costly choice
from a client-performance perspective. Most applications should work quite reliably using a combination of
<tt>idleConnectionTestPeriod</tt> and <tt>testConnectionsOnCheckIn</tt>. Both the idle test and the check-in
test are performed asynchronously, which leads to better performance, both perceived and actual.
</p>
<p>
Note that for many applications, high performance is more important than the risk of an occasional database exception.
In its default configuration, c3p0 does no Connection testing at all. Setting a fairly long
<tt>idleConnectionTestPeriod</tt>, and not testing on checkout and check-in at all is an excellent, high-performance
approach.
</p>
<h3>
<a name="configuring_statement_pooling">Configuring Statement Pooling</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 implements transparent PreparedStatement pooling as defined by the JDBC spec. Under some circumstances,
statement pooling can dramatically improve application performance. Under other circumstances, the overhead of
statement pooling can slightly harm
performance. Whether and how much statement pooling will help depends on how much
parsing, planning, and optimizing of queries your databases does when the statements are prepared.
Databases (and JDBC drivers) vary widely
in this respect. It's a good idea to benchmark your application with and without statement pooling to
see if and how much it helps.
</p>
<p>
You configure statement pooling in c3p0 via the following
configuration parameters:
</p>
<ul>
<li><a class="cfg_param" href="#maxStatements">maxStatements</a></li>
<li><a class="cfg_param" href="#maxStatementsPerConnection">maxStatementsPerConnection</a></li>
<li><a class="cfg_param" href="#statementCacheNumDeferredCloseThreads">statementCacheNumDeferredCloseThreads</a></li>
</ul>
<p>
<tt>maxStatements</tt> is JDBC's standard parameter for controlling statement pooling. <tt>maxStatements</tt> defines the
total number <tt>PreparedStatements</tt> a DataSource will cache. The pool will destroy the least-recently-used PreparedStatement
when it hits this limit. This sounds simple, but it's actually a strange approach, because
cached statements conceptually belong to individual Connections; they are not global resources. To figure out a size
for <tt>maxStatements</tt> that does not "churn" cached statements, you need to consider the number of <i>frequently used</i>
PreparedStatements in your application, and multiply that by the number of Connections you expect in the pool (<tt>maxPoolSize</tt>
in a busy application).
</p>
<p>
<tt>maxStatementsPerConnection</tt> is a non-standard configuration parameter that makes a bit more
sense conceptually. It defines how many statements each pooled Connection is allowed to own.
You can set this to a bit more than the number of <tt>PreparedStatements</tt> your application <i>frequently</i>
uses, to avoid churning.
</p>
<p>
If either of these parameters are greater than zero, statement pooling will be enabled. If both
parameters are greater than zero, both limits will be enforced. If only one is greater than zero, statement pooling
will be enabled, but only one limit will be enforced.
</p>
<p>
If <tt>statementCacheNumDeferredCloseThreads</tt> is greater than zero, the Statement pool will defer physically close()ing cached Statements until
its parent Connection is not in use by any client or internally (in e.g. a test) by the pool itself. For some JDBC drivers
(especially Oracle), attempts to close a Statement freeze if the parent Connection is in use. This parameter defaults to 0.
Set it to a positive value if you observe "APPARENT DEADLOCKS" realted to Connection close tasks. Almost always, that value should
be one: if you need more than one Thread dedicated solely to Statement destruction, you probably should set <tt>maxStatements</tt> and/or
<tt>maxStatementsPerConnection</tt> to higher values so you don't churn through cached Statements so quickly.
</p>
<h3>
<a name="configuring_recovery">Configuring Recovery From Database Outages</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 DataSources are designed (and configured by default) to recover from temporary database outages, such as
those which occur during a database restart or brief loss of network connectivity.
You can affect how c3p0 handles errors in acquiring Connections via the following
configurable properties:
</p>
<ul>
<li><a class="cfg_param" href="#acquireRetryAttempts">acquireRetryAttempts</a></li>
<li><a class="cfg_param" href="#acquireRetryDelay">acquireRetryDelay</a></li>
<li><a class="cfg_param" href="#breakAfterAcquireFailure">breakAfterAcquireFailure</a></li>
</ul>
<p>
When a c3p0 DataSource attempts and fails to acquire a Connection, it will retry up
to <tt>acquireRetryAttempts</tt> times, with a delay of <tt>acquireRetryDelay</tt>
between each attempt. If all attempts fail, any clients waiting for Connections from
the DataSource will see an Exception, indicating that a Connection could not be acquired.
Note that clients do not see any Exception until a full round of attempts fail, which
may be some time after the initial Connection attempt. If <tt>acquireRetryAttempts</tt>
is set to 0, c3p0 will attempt to acquire new Connections indefinitely, and calls to
<tt>getConnection()</tt> may block indefinitely waiting for a successful acquisition.
</p>
<p>
Once a full round of acquisition attempts fails, there are two possible policies. By
default, the c3p0 DataSource will remain active, and will try again to acquire Connections
in response to future requests for Connections. If you set <tt>breakAfterAcquireFailure</tt>
to <tt>true</tt>, the DataSource will consider itself broken after a failed round of
Connection attempts, and future client requests will fail immediately.
</p>
<p>
Note that if a database restart occurs, a pool may contain previously acquired but now
stale Connections. By default, these stale Connections will only be detected and
purged lazily, when an application attempts to use them, and sees an Exception. Setting
<tt>maxIdleTime</tt> or <tt>maxConnectionAge</tt> can help speed up the replacement of
broken Connections. (See <a href="#managing_pool_size">Managing ConnectionAge</a>.)
If you wish to avoid application Exceptions entirely, you must adopt a connection testing strategy that
is likely to detect stale Connections prior to their delivery to clients. (See
"<a href="#configuring_connection_testing">Configuring Connection Testing</a>".) Even
with active Connection testing (<tt>testConnectionsOnCheckout</tt> set to <tt>true</tt>, or
<tt>testConnectionsOnCheckin</tt> and a short <tt>idleConnectionTestPeriod</tt>), your
application may see occasional Exceptions on database restart, for example if the restart
occurs after a Connection to the database has already been checked out.
</p>
<h3>
<a name="connection_customizers">Managing Connection Lifecycles with Connection Customizer</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
Application frequently wish to set up Connections in some standard, reusable way immediately after
Connection acquisitions. Examples of this include setting-up character encodings, or date and time
related behavior, using vendor-specific APIs or non-standard SQL statement executions. Occasionally
it is useful to override the default values of standard Connection properties such as <tt>transactionIsolation</tt>,
<tt>holdability</tt>, or <tt>readOnly</tt>. c3p0 provides a "hook" interface that you can implement,
which gives you the opportunity to modify or track Connections just after they are checked out from the
database, immediately just prior to being handed to clients on checkout, just prior to being returned
to the pool on check-in, and just prior to final destruction by the pool. The Connections handed
to ConnectionCustomizers are raw, physical Connections, with all vendor-specific API accessible.
See the API docs for <a href="apidocs/com/mchange/v2/c3p0/ConnectionCustomizer.html"><tt>ConnectionCustomizer</tt></a>.
</p>
<p>
To install a <tt>ConnectionCustomizer</tt> just implement the interface, make your class accessible
to c3p0's ClassLoader, and set the configuration parameter below:
</p>
<ul>
<li><a class="cfg_param" href="#connectionCustomizerClassName">connectionCustomizerClassName</a></li>
</ul>
<p>
ConnectionCustomizers are required to be immutable classes with public no argument constructors.
They shouldn't store any state. For (rare) applications that wish to track the behavior of individual
DataSources with ConnectionCustomizers, the lifecycle methods each accept a DataSource-specific
"identityToken", which is unique to each PooledDataSource.
</p>
<p>
Below is a sample <tt>ConnectionCustomizer</tt>. Implementations that do not need to override all
four <tt>ConnectionCustomizer</tt> methods can extend
<a href="apidocs/com/mchange/v2/c3p0/AbstractConnectionCustomizer.html"><tt>AbstractConnectionCustomizer</tt></a>
to inherit no-op implementations of all methods.
</p>
<div class="example">
import com.mchange.v2.c3p0.*;
import java.sql.Connection;
public class VerboseConnectionCustomizer
{
public void onAcquire( Connection c, String pdsIdt )
{
System.err.println("Acquired " + c + " [" + pdsIdt + "]");
// override the default transaction isolation of
// newly acquired Connections
c.setTransactionIsolation( Connection.REPEATABLE_READ );
}
public void onDestroy( Connection c, String pdsIdt )
{ System.err.println("Destroying " + c + " [" + pdsIdt + "]"); }
public void onCheckOut( Connection c, String pdsIdt )
{ System.err.println("Checked out " + c + " [" + pdsIdt + "]"); }
public void onCheckIn( Connection c, String pdsIdt )
{ System.err.println("Checking in " + c + " [" + pdsIdt + "]"); }
}
</div>
<h3>
<a name="configuring_unresolved">Configuring Unresolved Transaction Handling</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
Connections checked into a pool cannot have any unresolved transactional work associated with them.
If users have set <tt>autoCommit</tt> to <tt>false</tt> on a Connection, and c3p0 cannot guarantee
that there is no pending transactional work, c3p0 must either <tt>rollback()</tt> or <tt>commit()</tt>
on check-in (when a user calls <tt>close()</tt>). The JDBC spec is (unforgivably) silent on the question
of whether unresolved work should be committed or rolled back on Connection close. By default, c3p0
rolls back unresolved transactional work when a user calls <tt>close()</tt>.
</p>
<p>
You can adjust this behavior via the following configuration properties:
</p>
<ul>
<li><a class="cfg_param" href="#autoCommitOnClose">autoCommitOnClose</a></li>
<li><a class="cfg_param" href="#forceIgnoreUnresolvedTransactions">forceIgnoreUnresolvedTransactions</a></li>
</ul>
<p>
If you wish c3p0 to allow unresolved transactional work to commit on checkin, set <tt>autoCommitOnClose</tt>
to true. If you wish c3p0 to leave transaction management to you, and neither commit nor rollback (nor modify
the state of Connection <tt>autoCommit</tt>), you may set <tt>forceIgnoreUnresolvedTransactions</tt> to true. Setting
<tt>forceIgnoreUnresolvedTransactions</tt> is strongly discouraged, because if clients are not careful to
commit or rollback themselves prior to close(), or do not set Connection <tt>autoCommit</tt> consistently, bizarre
unreproduceable behavior and database lockups can occur.
</p>
<h3>
<a name="configuring_to_debug_and_workaround_broken_clients">Configuring to Debug and Workaround Broken Client Applications</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
Sometimes client applications are sloppy about close()ing all Connections they check out. Eventually,
the pool grows to <tt>maxPoolSize</tt>, and then runs out of Connections, because of these bad clients.
</p>
<p>
The right way to address this problem is to fix the client application. <tt>c3p0</tt> can help you debug,
by letting you know where Connections are checked out that occasionally don't get checked in. In rare and
unfortunate situations, development of the client application is closed, and even though it is buggy, you cannot fix it.
c3p0 can help you work around the broken application, preventing it from exhausting the pool.
</p>
<p>
The following parameters can help you debug or workaround broken client applications.
</p>
<ul>
<li><a class="cfg_param" href="#debugUnreturnedConnectionStackTraces">debugUnreturnedConnectionStackTraces</a></li>
<li><a class="cfg_param" href="#unreturnedConnectionTimeout">unreturnedConnectionTimeout</a></li>
</ul>
<p>
<tt>unreturnedConnectionTimeout</tt> defines a limit (in seconds) to how long a Connection may remain checked out.
If set to a nozero value, unreturned, checked-out Connections that exceed this limit will be summarily destroyed,
and then replaced in the pool.
Obviously, you must take care to set this parameter to a value large enough that all intended operations
on checked out Connections have time to complete.
You can use this parameter to merely workaround unreliable client apps that fail to
close() Connections.
</p>
<p>
Much better than working-around is fixing. If, <i>in addition to setting</i> <tt>unreturnedConnectionTimeout</tt>,
you set <tt>debugUnreturnedConnectionStackTraces</tt> to <tt>true</tt>,
then a stack trace will be captured
each time a Connection is checked-out. Whenever an unreturned Connection times out, that stack trace will be
printed, revealing where a Connection was checked out that was not checked in promptly. <tt>debugUnreturnedConnectionStackTraces</tt>
is intended to be used only for debugging, as capturing a stack trace can slow down Connection check-out.
</p>
<h3>
<a name="other_ds_configuration">Other DataSource Configuration</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
See <a href="#configuration_properties">Appendix A</a> for information about the following configuration properties:
</p>
<ul>
<li><a class="cfg_param" href="#checkoutTimeout">checkoutTimeout</a></li>
<li><a class="cfg_param" href="#factoryClassLocation">factoryClassLocation</a></li>
<li><a class="cfg_param" href="#maxAdministrativeTaskTime">maxAdministrativeTaskTime</a></li>
<li><a class="cfg_param" href="#numHelperThreads">numHelperThreads</a></li>
<li><a class="cfg_param" href="#usesTraditionalReflectiveProxies"><s>usesTraditionalReflectiveProxies</s></a></li>
</ul>
<p>
<tt>numHelperThreads</tt> and <tt>maxAdministrativeTaskTime</tt> help to configure the behavior
of DataSource thread pools. By default, each DataSource has only three associated helper threads.
If performance seems to drag under heavy load, or if you observe via JMX or direct inspection of
a <tt>PooledDataSource</tt>, that the number of "pending tasks" is usually greater than zero, try
increasing <tt>numHelperThreads</tt>. <tt>maxAdministrativeTaskTime</tt> may be useful for users
experiencing tasks that hang indefinitely and "APPARENT DEADLOCK" messages. (See Appendix A for more.)
</p>
<p>
<tt>checkoutTimeout</tt> limits how long a client will wait for a Connection, if all Connections are
checked out and one cannot be supplied immediately. <tt>usesTraditionalReflectiveProxies</tt> is
of little practical use and is now formally deprecated. It permits you to use an old, now superceded
implementation of C3P0-generated proxy objects. (C3P0
used to use reflective, dynamic proxies. Now, for enhanced performance, it uses code-generated, nonrefective
implementations.) <tt>factoryClassLocation</tt> can be used to indicate where a URL from which c3p0 classes
can be downloaded, if c3p0 DataSources will be retrieved as References from a JNDI DataSource by clients
who do not have c3p0 locally installed.
</p>
<h3>
<a name="jmx_configuration_and_management">Configuring and Managing c3p0 via JMX</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
If JMX libraries and a JMX MBeanServer are available in your environment (they are include in JDK 1.5 and above),
you can inspect and configure your c3p0 datasources via a JMX administration tool (such as jconsole, bundled with
jdk 1.5). You will find that c3p0 registers MBeans under <tt>com.mchange.v2.c3p0</tt>, one with statistics about the
library as a whole (called <tt>C3P0Registry</tt>), and an MBean for each <tt>PooledDataSource</tt> you deploy. You can view and
modify your DataSource's configuration properties, track the activity of Connection, Statement, and Thread pools, and reset
pools and DataSources via the <tt>PooledDataSource</tt> MBean. (You may wish to view the API docs of
<a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html"><tt>PooledDataSource</tt></a> for documentation of
the available operations.)
</p>
<p>
The name under which mbeans for c3p0 PooledDataSources will be registered includes the property
<a class="cfg_param" href="#dataSourceName">dataSourceName</a>.
So, if you set this property, you can ensure that semanically equivalent data sources
are identifiable across application restarts.
</p>
<p>
If you do not want c3p0 to register MBeans with your JMX environment, you can suppress this
behavior with the following, set either as a System property or in <tt>c3p0.properties</tt>:
</p>
<div class="example">
com.mchange.v2.c3p0.management.ManagementCoordinator=com.mchange.v2.c3p0.management.NullManagementCoordinator
</div>
<h3>
<a name="configuring_logging">Configuring Logging</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 uses a custom logging library similar to jakarta commons-logging. Log messages can be directed to
the popular log4j logging library, to the standard logging facility introduced with jdk1.4, or to
<tt>System.err</tt>. Nearly all configuration should be done at the level of your preferred logging
library. There are a very few configuration options specific to c3p0's logging, and usually the defaults
will be fine. Logging-related parameters
may be placed in your <tt>c3p0.properties</tt> file, in a file called <tt>mchange-log.properties</tt> at
the top-level of your classpath, or they may be defined as System properties. (The logging properties defined
below may <u>not</u> be defined in <tt>c3p0-config.xml</tt>!) See the
<a href="#log_properties_box">box</a> below.
</p>
<p>
c3p0's logging behavior is affected by certain build-time options. If build-option <tt>c3p0.debug</tt> is set
to <tt>false</tt>, all messages at a logging level below INFO will be suppressed. Build-option <tt>c3p0.trace</tt> controls how fine-grained c3p0's below
INFO level reporting will be. For the moment, distributed
c3p0 binaries are compiled with <tt>debug</tt> set to <tt>true</tt> and <tt>trace</tt> set to its maximum level of <tt>10</tt>.
But binaries may eventually be
distributed with <tt>debug</tt> set to <tt>false</tt>. (For the moment, the performance impact of the logging level-checks seems
very small, and it's most flexible to compile in all the messages, and let your logging library control which are emitted.) When
c3p0 starts up, it emits the build-time values of debug and trace, along with the version and build time.
</p>
<dl class="log_properties">
<a name="log_properties_box"></a>
<dt><a name="com.mchange.v2.log.MLog" />com.mchange.v2.log.MLog</dt>
<dd>
<div class="propdesc">
Determines which library c3p0 will output log messages to. By default, if log4j is available,
it will use that library, otherwise if jdk1.4 logging apis are available it will use those,
and if neither are available, it will use a simple fallback that logs to <tt>System.err</tt>.
If you want to directly control which library is used, you may set this property to one of:
<ul>
<li><tt>com.mchange.v2.log.log4j.Log4jMLog</tt></li>
<li><tt>com.mchange.v2.log.jdk14logging.Jdk14MLog</tt></li>
<li><tt>com.mchange.v2.log.FallbackMLog</tt></li>
</ul>
You may also set this property to a comma separated list of the above alternatives, to
define an order of preference among logging libraries.
</div>
</dd>
<dt><a name="com.mchange.v2.log.NameTransformer" />com.mchange.v2.log.NameTransformer</dt>
<dd>
<div class="propdesc">
By default, c3p0 uses very fine-grained logging, in general with one logger for each
c3p0 class. For a variety of reasons, some users may prefer fewer, more global loggers.
You may opt for one-logger-per-package by setting <tt>com.mchange.v2.log.NameTransformer</tt>
to the value <tt>com.mchange.v2.log.PackageNames</tt>. Advanced users can also define
other strategies for organizing the number and names of loggers by setting this variable
to the fully-qualified class name of a custom implementation of the
<tt>com.mchange.v2.log.NameTransformer</tt> interface.
</div>
</dd>
<dt><a name="com.mchange.v2.log.FallbackMLog.DEFAULT_CUTOFF_LEVEL" />com.mchange.v2.log.FallbackMLog.DEFAULT_CUTOFF_LEVEL</dt>
<dd>
<div class="propdesc">
If, whether by choice or by necessity, you are using c3p0's <tt>System.err</tt> fallback logger, you can
use this parameter to control how detailed c3p0's logging should be. Any of the following values (taken
from the jdk1.4 logging library) are acceptable:
<ul>
<li><tt>OFF</tt></li>
<li><tt>SEVERE</tt></li>
<li><tt>WARNING</tt></li>
<li><tt>INFO</tt></li>
<li><tt>CONFIG</tt></li>
<li><tt>FINE</tt></li>
<li><tt>FINER</tt></li>
<li><tt>FINEST</tt></li>
<li><tt>ALL</tt></li>
</ul>
This property defaults to <tt>INFO</tt>.
</div>
</dd>
</dl>
</div>
<h2><a name="performance">Performance</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
Enhanced performance is the purpose of Connection and Statement pooling, and a
major goal of the c3p0 library. For most applications, Connection pooling
will provide a significant performance gain, especially if you are acquiring
an unpooled Connection for each client access. If you are letting a single,
shared Connection serve many clients to avoid Connection acquisition overhead,
you may suffer performance issues and problems managing transactions when
your Connection is under concurrent load; Connection pooling will enable you
to switch to a one Connection-per-client model with little or no cost.
If you are writing Enterprise Java Beans, you may be tempted to acquire a
Connection once and not return it until the bean is about to be destroyed or
passivated. But this can be resource-costly, as dormant pooled
beans needlessly hold the Connection's network and database resources.
Connection pooling permits beans to only "own"
a Connection while they are using it.
</p>
<p>
But, there are performance costs to c3p0 as well. In order to implement
automatic cleanup of unclosed <tt>ResultSets</tt> and <tt>Statements</tt> when parent resources
are returned to pools, all client-visible <tt>Connections</tt>, <tt>ResultSets</tt>, <tt>Statements</tt>
are really wrappers around objects provided by an underlying unpooled DataSource
or "traditional" JDBC driver. Thus, there is some extra overhead to all JDBC calls.
</p>
<p>
Some attention has been paid to minimizing the "wrapper" overhead of c3p0. In
my environment, the wrapper overhead amounts from several hundreths to several
thousandths of the cost of Connection acquisition, so unless you are making
many, many JDBC calls in fast succession, there will be a net
gain in performance and resource-utilization efficiency.
Significantly, the overhead associated with ResultSet operations (where
one might iterate through a table with thousands of records) appears to be
negligibly small.
</p>
</div>
<h2><a name="known_shortcomings">Known Shortcomings</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<ul>
<li>
<p>
Connections and Statements are pooled on a per-authentication basis.
So, if one pool-backed DataSource is used to acquire Connections both
for [<tt>user</tt>=alice, <tt>password</tt>=secret1] and [<tt>user</tt>=bob, <tt>password</tt>=secret2],
there will be two distinct pools, and the DataSource might in the
worst case manage twice the number of Connections specified by the
<tt>maxPoolSize</tt> property.
</p>
<p>
This fact is a natural consequence of the definition of the DataSource spec (which
allows Connections to be acquired with multiple user authentications), and the
requirement that all Connections in a single pool be functionally identical.
This "issue" will not be changed or fixed. It's noted here just so you understand
what's going on.
</p>
</li>
<li>
<p>
The overhead of Statement pooling is too high. For drivers that
do not perform significant preprocessing of PreparedStatements, the
pooling overhead outweighs any savings. Statement pooling is thus
turned off by default. If your driver does preprocess <tt>PreparedStatements</tt>,
especially if it does so via IPC with the RDBMS, you will probably
see a significant performance gain by turning Statement pooling on. (Do this by
setting the configuration property <tt>maxStatements</tt> or <tt>maxStatementsPerConnection</tt>
to a value greater than zero.).
</p>
</li>
</ul>
</div>
<h2><a name="feedback_and_support">Feedback and Support</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
Please provide any and all feedback to <<a href="mailto:swaldman@mchange.com">swaldman@mchange.com</a>>!
Also, feel free to join and ask questions on the <tt>c3p0-users</tt> mailing list.
Sign up at <a href="http://sourceforge.net/projects/c3p0/">http://sourceforge.net/projects/c3p0/</a>
</p>
<p>
Thank you for using c3p0!!!
</p>
</div>
<h2><a name="configuration_properties">Appendix A: Configuration Properties</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
c3p0 configuration properties can be divided into <a href="#javabeans-style-properties">JavaBeans-style Properties</a> and
<a href="#other-properties">Other Properties</a>.
</p>
<h3>
<a name="javabeans-style-properties">JavaBeans-style Properties</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
The following properties can be set directly in code as JavaBeans properties,
via a <a href="#system_properties">System properties</a> or a <a href="#c3p0_properties"><tt>c3p0.properties</tt></a> file
(with <tt>c3p0.</tt> prepended to
the property name), or in a <a href="#c3p0-config.xml"><tt>c3p0-config.xml</tt></a> file. See the section on
<a href="#configuration">Configuration</a> above.
Click on the property name for a full description.
</p>
<table class="beanPropSummaryTable">
<tr>
<td>
<a href="#acquireIncrement">acquireIncrement</a><br/>
<a href="#acquireRetryAttempts">acquireRetryAttempts</a><br/>
<a href="#acquireRetryDelay">acquireRetryDelay</a><br/>
<a href="#autoCommitOnClose">autoCommitOnClose</a><br/>
<a href="#automaticTestTable">automaticTestTable</a><br/>
<a href="#breakAfterAcquireFailure">breakAfterAcquireFailure</a><br/>
<a href="#checkoutTimeout">checkoutTimeout</a><br/>
<a href="#connectionCustomizerClassName">connectionCustomizerClassName</a><br/>
<a href="#connectionTesterClassName">connectionTesterClassName</a><br/>
<a href="#dataSourceName">dataSourceName</a><br/>
<a href="#debugUnreturnedConnectionStackTraces">debugUnreturnedConnectionStackTraces</a><br/>
<a href="#factoryClassLocation">factoryClassLocation</a><br/>
</td>
<td>
<a href="#forceIgnoreUnresolvedTransactions">forceIgnoreUnresolvedTransactions</a><br/>
<a href="#idleConnectionTestPeriod">idleConnectionTestPeriod</a><br/>
<a href="#initialPoolSize">initialPoolSize</a><br/>
<a href="#maxAdministrativeTaskTime">maxAdministrativeTaskTime</a><br/>
<a href="#maxConnectionAge">maxConnectionAge</a><br/>
<a href="#maxIdleTime">maxIdleTime</a><br/>
<a href="#maxIdleTimeExcessConnections">maxIdleTimeExcessConnections</a><br/>
<a href="#maxPoolSize">maxPoolSize</a><br/>
<a href="#maxStatements">maxStatements</a><br/>
<a href="#maxStatementsPerConnection">maxStatementsPerConnection</a><br/>
<a href="#minPoolSize">minPoolSize</a><br/>
</td>
<td>
<a href="#numHelperThreads">numHelperThreads</a><br/>
<a href="#overrideDefaultUser">overrideDefaultUser</a><br/>
<a href="#overrideDefaultPassword">overrideDefaultPassword</a><br/>
<a href="#password">password</a><br/>
<a href="#preferredTestQuery">preferredTestQuery</a><br/>
<a href="#propertyCycle">propertyCycle</a><br/>
<a href="#statementCacheNumDeferredCloseThreads">statementCacheNumDeferredCloseThreads</a><br/>
<a href="#testConnectionOnCheckin">testConnectionOnCheckin</a><br/>
<a href="#testConnectionOnCheckout">testConnectionOnCheckout</a><br/>
<a href="#unreturnedConnectionTimeout">unreturnedConnectionTimeout</a><br/>
<a href="#user">user</a><br/>
<a href="#usesTraditionalReflectiveProxies"><s>usesTraditionalReflectiveProxies</s></a><br/>
</td>
</tr>
</table>
<dl class="properties">
<dt><a name="acquireIncrement" />acquireIncrement</dt>
<dd>
<div class="default">Default: 3</div>
<div class="propdesc">
Determines how many connections at a time c3p0 will try to acquire when the pool is exhausted.
[See <a href="#basic_pool_configuration">"Basic Pool Configuration"</a>]
</div>
</dd>
<dt><a name="acquireRetryAttempts" />acquireRetryAttempts</dt>
<dd>
<div class="default">Default: 30</div>
<div class="propdesc">
Defines how many times c3p0 will try to acquire a new Connection from the database before giving up. If
this value is less than or equal to zero, c3p0 will keep trying to fetch a Connection indefinitely.
[See <a href="#configuring_recovery">"Configuring Recovery From Database Outages"</a>]
</div>
</dd>
<dt><a name="acquireRetryDelay" />acquireRetryDelay</dt>
<dd>
<div class="default">Default: 1000</div>
<div class="propdesc">
Milliseconds, time c3p0 will wait between acquire attempts.
[See <a href="#configuring_recovery">"Configuring Recovery From Database Outages"</a>]
</div>
</dd>
<dt><a name="autoCommitOnClose" />autoCommitOnClose</dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
The JDBC spec is unforgivably silent on what should happen to unresolved, pending
transactions on Connection close. C3P0's default policy is to rollback any uncommitted, pending
work. (I think this is absolutely, undeniably the right policy, but there is no consensus among JDBC driver vendors.)
Setting <tt>autoCommitOnClose</tt> to true causes uncommitted pending work to be committed, rather than rolled
back on Connection close. [<i>Note: Since the spec is absurdly unclear on this question, application authors who wish
to avoid bugs and inconsistent behavior should ensure that all transactions are explicitly either committed or
rolled-back before close is called.</i>]
[See <a href="#configuring_unresolved">"Configuring Unresolved Transaction Handling"</a>]
</div>
</dd>
<dt><a name="automaticTestTable" />automaticTestTable</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
If provided, c3p0 will create an empty table of the specified name, and use queries against that table to
test the Connection. If <tt>automaticTestTable</tt> is provided, c3p0 will generate its own test query, therefore
any <tt>preferredTestQuery</tt> set will be ignored. You should not work with the named table after c3p0 creates
it; it should be strictly for c3p0's use in testing your Connection. (If you define your own ConnectionTester, it
must implement the <a href="apidocs/com/mchange/v2/c3p0/QueryConnectionTester.html">QueryConnectionTester</a>
interface for this parameter to be useful.) [See <a href="#configuring_connection_testing">"Configuring Connection Testing"</a>]
</div>
</dd>
<dt><a name="breakAfterAcquireFailure" />breakAfterAcquireFailure</dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
If true, a pooled DataSource will declare itself broken and be permanently closed if
a Connection cannot be obtained from the database after making <tt>acquireRetryAttempts</tt> to acquire one.
If false, failure to obtain a Connection will cause all Threads waiting for the pool to acquire a Connection
to throw an Exception, but the DataSource will remain valid, and will attempt to acquire again following
a call to <tt>getConnection()</tt>.
[See <a href="#configuring_recovery">"Configuring Recovery From Database Outages"</a>]
</div>
</dd>
<dt><a name="checkoutTimeout" />checkoutTimeout</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
The number of milliseconds a client calling getConnection() will wait for a Connection to be checked-in or acquired
when the pool is exhausted. Zero means wait indefinitely. Setting any positive value will cause the getConnection()
call to time-out and break with an <tt>SQLException</tt> after the specified number of milliseconds.
</div>
</dd>
<dt><a name="connectionCustomizerClassName" />connectionCustomizerClassName</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
The fully qualified class-name of an implememtation of the <a href="apidocs/com/mchange/v2/c3p0/ConnectionCustomizer.html"><tt>ConnectionCustomizer</tt></a>
interface, which users can implement to set up Connections when they are acquired from the database, or on check-out, and potentially
to clean things up on check-in and Connection destruction. If standard Connection properties (holdability, readOnly, or transactionIsolation)
are set in the ConnectionCustomizer's onAcquire() method, these will override the Connection default values.
</div>
</dd>
<dt><a name="connectionTesterClassName" />connectionTesterClassName</dt>
<dd>
<div class="default">Default: com.mchange.v2.c3p0.impl.DefaultConnectionTester</div>
<div class="propdesc">
The fully qualified class-name of an implememtation of the <a href="apidocs/com/mchange/v2/c3p0/ConnectionTester.html"><tt>ConnectionTester</tt></a>
interface, or <a href="apidocs/com/mchange/v2/c3p0/QueryConnectionTester.html"><tt>QueryConnectionTester</tt></a> if you would like instances
to have access to a user-configured <tt>preferredTestQuery</tt>. This can be used to customize how c3p0 DataSources test Connections, but with
the introduction of <tt>automaticTestTable</tt> and <tt>preferredTestQuery</tt> configuration parameters, "rolling your own" should be overkill
for most users.
[See <a href="#configuring_connection_testing">"Configuring Connection Testing"]</a>
</div>
</dd>
<dt><a name="dataSourceName" />dataSourceName</dt>
<dd>
<div class="default">Default: if configured with a <a href="#c3p0-config.xml">named config</a>, the config name, otherwise the pool's "identity token"</div>
<div class="propdesc">
Every c3p0 pooled data source is given a <tt>dataSourceName</tt>, which serves two purposes. It helps users find DataSources via
<a href="#using_c3p0_registry_box">C3P0Registry</a>, and it is included in the name of JMX mBeans in order to help
track and distinguish between multiple c3p0 DataSources even across application or JVM restarts. <tt>dataSourceName</tt>
defaults to the pool's configuration name, if a <a href="#c3p0-config.xml">named config</a> was used, or else to an "identity token" (an
opaque, guaranteed unique String associated with every c3p0 DataSource). You may update this property to any name you find convenient.
<tt>dataSourceName</tt> is <i>not</i> guaranteed to be unique — for example, multiple DataSource created from the same named
configuration will share the same <tt>dataSourceName</tt>. But if you are going to make use of <tt>dataSourceName</tt>,
you will probably want to ensure that all pooled DataSources within your JVM do have unique names.
</div>
</dd>
<dt><a name="debugUnreturnedConnectionStackTraces" />debugUnreturnedConnectionStackTraces</dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
If true, and if <tt><a href="#unreturnedConnectionTimeout">unreturnedConnectionTimeout</a></tt> is set to a positive value,
then the pool will capture the stack trace (via an Exception) of all Connection checkouts, and the stack traces will be
printed when unreturned checked-out Connections timeout. This is intended to debug applications with Connection leaks, that
is applications that occasionally fail to return Connections, leading to pool growth, and eventually exhaustion (when the
pool hits <tt>maxPoolSize</tt> with all Connections checked-out and lost). This parameter should only be set while debugging,
as capturing the stack trace will slow down every Connection check-out.
[See <a href="#configuring_to_debug_and_workaround_broken_clients">"Configuring to Debug and Workaround Broken Client Applications"</a>]
</div>
</dd>
<dt><a name="factoryClassLocation" />factoryClassLocation</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
DataSources that will be bound by JNDI and use that API's Referenceable interface
to store themselves may specify a URL from which the class capable of dereferencing
a them may be loaded. If (as is usually the case) the c3p0 libraries will be locally
available to the JNDI service, leave this set as null.
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
</dd>
<dt><a name="forceIgnoreUnresolvedTransactions" />forceIgnoreUnresolvedTransactions</dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
<b><i>Strongly disrecommended. Setting this to <tt>true</tt> may lead to subtle and bizarre bugs.</i></b>
This is a terrible setting, leave it alone unless absolutely necessary. It is here to workaround
broken databases / JDBC drivers that do not properly support transactions, but that allow Connections'
<tt>autoCommit</tt> flags to go to false regardless. If you are using a database that supports transactions
"partially" (this is oxymoronic, as the whole point of transactions is to perform operations reliably and
completely, but nonetheless such databases are out there), if you feel comfortable ignoring the fact that Connections
with <tt>autoCommit == false</tt> may be in the middle of transactions and may hold locks and other resources,
you may turn off c3p0's wise default behavior, which is to protect itself, as well as the usability and consistency
of the database, by either rolling back (default) or committing (see <tt>c3p0.autoCommitOnClose</tt> <i>above</i>)
unresolved transactions. <b>This should only be set to true when you are sure you are using a database that
allows Connections' autoCommit flag to go to false, but offers no other meaningful support of transactions. Otherwise
setting this to true is just a bad idea.</b>
[See <a href="#configuring_unresolved">"Configuring Unresolved Transaction Handling"</a>]
</div>
</dd>
<dt><a name="idleConnectionTestPeriod"/>idleConnectionTestPeriod</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
If this is a number greater than 0, c3p0 will test all idle, pooled but unchecked-out connections,
every this number of seconds. [See <a href="#configuring_connection_testing">"Configuring Connection Testing"</a>]
</div>
</dd>
<dt><a name="initialPoolSize"/>initialPoolSize</dt>
<dd>
<div class="default">Default: 3</div>
<div class="propdesc">
Number of Connections a pool will try to acquire upon startup. Should be between <tt>minPoolSize</tt> and
<tt>maxPoolSize</tt>.
[See <a href="#basic_pool_configuration">"Basic Pool Configuration"</a>]
</div>
</dd>
<dt><a name="maxAdministrativeTaskTime" />maxAdministrativeTaskTime</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
Seconds before c3p0's thread pool will try to interrupt an apparently hung task. <u>Rarely useful.</u> Many of c3p0's functions
are not performed by client threads, but asynchronously by an internal thread pool. c3p0's asynchrony enhances
client performance directly, and minimizes the length of time that critical locks are held by ensuring that slow
jdbc operations are performed in non-lock-holding threads. If, however, some of these tasks "hang", that is
they neither succeed nor fail with an Exception for a prolonged period of time, c3p0's thread pool can become
exhausted and administrative tasks backed up. If the tasks are simply slow, the best way to resolve the problem
is to increase the number of threads, via <a href="#numHelperThreads">numHelperThreads</a>. But if tasks
sometimes hang indefinitely, you can use this parameter to force a call to the task thread's <tt>interrupt()</tt>
method if a task exceeds a set time limit. [c3p0 will eventually recover from hung tasks anyway by signalling an "APPARENT
DEADLOCK" (you'll see it as a warning in the logs), replacing the thread pool task threads, and interrupt()ing the
original threads. But letting the pool go into APPARENT DEADLOCK and then recover means that for some periods,
c3p0's performance will be impaired. So if you're seeing these messages, increasing <a href="#numHelperThreads">numHelperThreads</a>
and setting <tt>maxAdministrativeTaskTime</tt> might help. <tt>maxAdministrativeTaskTime</tt> should be large enough
that any resonable attempt to acquire a Connection from the database, to test a Connection, or two destroy a Connection,
would be expected to succeed or fail within the time set. Zero (the default) means tasks are never interrupted,
which is the best and safest policy under most circumstances. If tasks are just slow, allocate more threads. If tasks
are hanging forever, try to figure out why, and maybe setting <tt>maxAdministrativeTaskTime</tt> can help in the meantime.
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
</dd>
<dt><a name="maxConnectionAge" />maxConnectionAge</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
Seconds, effectively a time to live. A Connection older than <tt>maxConnectionAge</tt> will be destroyed and
purged from the pool. This differs from <tt>maxIdleTime</tt> in that it refers to absolute age. Even a Connection
which has not been much idle will be purged from the pool if it exceeds <tt>maxConnectionAge</tt>. Zero means
no maximum absolute age is enforced.
</div>
</dd>
<dt><a name="maxIdleTime" />maxIdleTime</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
Seconds a Connection can remain pooled but unused before being discarded. Zero means idle connections never expire.
[See <a href="#basic_pool_configuration">"Basic Pool Configuration"</a>]
</div>
</dd>
<dt><a name="maxIdleTimeExcessConnections" />maxIdleTimeExcessConnections</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
Number of seconds that Connections in excess of <tt>minPoolSize</tt> should be permitted to remain idle in the pool
before being culled. Intended for applications that wish to aggressively minimize the number of open Connections,
shrinking the pool back towards minPoolSize if, following a spike, the load level diminishes and Connections
acquired are no longer needed. If <tt>maxIdleTime</tt> is set, <tt>maxIdleTimeExcessConnections</tt> should be
smaller if the parameter is to have any effect. Zero means no enforcement, excess Connections are not idled out.
</div>
</dd>
<dt><a name="maxPoolSize"/>maxPoolSize</dt>
<dd>
<div class="default">Default: 15</div>
<div class="propdesc">
Maximum number of Connections a pool will maintain at any given time.
[See <a href="#basic_pool_configuration">"Basic Pool Configuration"</a>]
</div>
</dd>
<dt><a name="maxStatements" />maxStatements</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
The size of c3p0's global PreparedStatement cache. If both <tt>maxStatements</tt> and <tt>maxStatementsPerConnection</tt>
are zero, statement caching will not be enabled. If <tt>maxStatements</tt> is zero but <tt>maxStatementsPerConnection</tt>
is a non-zero value, statement caching will be enabled, but no global limit will be enforced, only the per-connection maximum.
<tt>maxStatements</tt> controls the total number of Statements cached,
for all Connections. If set, it should be a fairly large number, as each pooled Connection requires its own,
distinct flock of cached statements. As a guide, consider how many distinct PreparedStatements are used
<i>frequently</i> in your application, and multiply that number by <tt>maxPoolSize</tt> to arrive at an appropriate
value. Though <tt>maxStatements</tt> is the JDBC standard parameter for controlling statement caching, users may
find c3p0's alternative <tt>maxStatementsPerConnection</tt> more intuitive to use.
[See <a href="#configuring_statement_pooling">"Configuring Statement Pooling"</a>]
</div>
</dd>
<dt><a name="maxStatementsPerConnection" />maxStatementsPerConnection</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
The number of PreparedStatements c3p0 will cache for a single pooled Connection.
If both <tt>maxStatements</tt> and <tt>maxStatementsPerConnection</tt>
are zero, statement caching will not be enabled. If <tt>maxStatementsPerConnection</tt> is zero but <tt>maxStatements</tt>
is a non-zero value, statement caching will be enabled, and a global limit enforced, but otherwise no limit will be set
on the number of cached statements for a single Connection.
If set, maxStatementsPerConnection should be set to about the number distinct PreparedStatements that are used
<i>frequently</i> in your application, plus two or three extra so infrequently statements don't force the more common
cached statements to be culled. Though <tt>maxStatements</tt> is the JDBC standard parameter for controlling statement caching,
users may find <tt>maxStatementsPerConnection</tt> more intuitive to use.
[See <a href="#configuring_statement_pooling">"Configuring Statement Pooling"</a>]
</div>
</dd>
<dt><a name="minPoolSize"/>minPoolSize</dt>
<dd>
<div class="default">Default: 3</div>
<div class="propdesc">
Minimum number of Connections a pool will maintain at any given time.
[See <a href="#basic_pool_configuration">"Basic Pool Configuration"</a>]
</div>
</dd>
<dt><a name="numHelperThreads" />numHelperThreads</dt>
<dd>
<div class="default">Default: 3</div>
<div class="propdesc">
c3p0 is very asynchronous. Slow JDBC operations are generally
performed by helper threads that don't hold contended locks. Spreading
these operations over multiple threads can significantly improve performance
by allowing multiple operations to be performed simultaneously.
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
</dd>
<dt><a name="overrideDefaultUser" />overrideDefaultUser</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
Forces the username that should by PooledDataSources when a user calls the default
getConnection() method. This is primarily useful when applications are pooling Connections
from a non-c3p0 unpooled DataSource. Applications that use <tt>ComboPooledDataSource</tt>,
or that wrap any c3p0-implemented unpooled DataSource can use the simple
<a href="#user">user</a> property.
<!--
C3P0 PooledDataSources, implicitly or explicity, are wrappers around unpooled DataSources.
For most users, the unpooled DataSource is c3p0's own DriverManagerDataSource, but users are
welcome to wrap other DataSource implementations. Per the JDBC 2.0 spec, DataSources may offer
standard properties "user" and "password". If present, c3p0 PooledDataSources use these properties
to determine what kind of authentication to use. If absent, PooledDataSources use the unpooled
DataSource's default getConnection() method. Some DataSources offer one but not both of the
standard properties, which confuses c3p0.
-->
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
</dd>
<dt><a name="overrideDefaultPassword" />overrideDefaultPassword</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
Forces the password that should by PooledDataSources when a user calls the default
getConnection() method. This is primarily useful when applications are pooling Connections
from a non-c3p0 unpooled DataSource. Applications that use <tt>ComboPooledDataSource</tt>,
or that wrap any c3p0-implemented unpooled DataSource can use the simple
<a href="#password">password</a> property.
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
</dd>
<dt><a name="password" />password</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
For applications using <tt>ComboPooledDataSource</tt> or any
c3p0-implemented unpooled DataSources — <tt>DriverManagerDataSource</tt> or the
DataSource returned by <tt>DataSources.unpooledDataSource( ... )</tt> —
defines the password that will be used for the DataSource's default
<tt>getConnection()</tt> method. (See also <a href="#user">user</a>.)
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
</dd>
<dt><a name="preferredTestQuery" />preferredTestQuery</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
Defines the query that will be executed for all connection tests, if the default ConnectionTester (or some
other implementation of <a href="apidocs/com/mchange/v2/c3p0/QueryConnectionTester.html">QueryConnectionTester</a>,
or better yet <a href="apidocs/com/mchange/v2/c3p0/FullQueryConnectionTester.html">FullQueryConnectionTester</a>)
is being used. Defining a <tt>preferredTestQuery</tt>
that will execute quickly in your database may dramatically speed up Connection tests. (If no <tt>preferredTestQuery</tt>
is set, the default ConnectionTester executes a <tt>getTables()</tt> call on the Connection's DatabaseMetaData.
Depending on your database, this may execute more slowly than a "normal" database query.)
<b>NOTE: The table against
which your <tt>preferredTestQuery</tt> will be run must exist in the database schema <i>prior</i> to your initialization
of your DataSource. If your application defines its own schema, try <tt>automaticTestTable</tt> instead.</b>
[See <a href="#configuring_connection_testing">"Configuring Connection Testing"</a>]
</div>
</dd>
<dt><a name="propertyCycle" />propertyCycle</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
Maximum time in seconds before user configuration constraints are enforced.
Determines how frequently <tt>maxConnectionAge</tt>, <tt>maxIdleTime</tt>, <tt>maxIdleTimeExcessConnections</tt>,
<tt>unreturnedConnectionTimeout</tt> are enforced. c3p0 periodically checks the age of Connections to
see whether they've timed out. This parameter determines the period. Zero means automatic: A suitable period
will be determined by c3p0. [You can call <tt>getEffectivePropertyCycle...()</tt> methods on a c3p0
<a href="apidocs/com/mchange/v2/c3p0/PooledDataSource.html">PooledDataSource</a> to find the period
automatically chosen.]
</div>
</dd>
<dt><a name="statementCacheNumDeferredCloseThreads" />statementCacheNumDeferredCloseThreads</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
If set to a value greater than 0, the statement cache will track when Connections are in use, and only destroy
Statements when their parent Connections are not otherwise in use. Although closing of
a Statement while the parent Connection is in use is formally within spec, some databases
and/or JDBC drivers, most notably Oracle, do not handle the case well and freeze, leading
to deadlocks. Setting this parameter to a positive value should eliminate the issue. This parameter
should only be set if you observe that attempts by c3p0 to close() cached statements freeze (usually
you'll see <tt>APPARENT DEADLOCKS</tt> in your logs). If set, this parameter should almost always be set to <tt>1</tt>.
Basically, if you need more than one Thread dedicated solely to destroying cached Statements, you should set <tt>maxStatements</tt>
and/or <tt>maxStatementsPerConnection</tt> so that you don't churn through Statements so quickly.
[See <a href="#configuring_statement_pooling">"Configuring Statement Pooling"</a>]
<div class="per-user">Does Not Support Per-User Overrides.</div>
</div>
</dd>
<dt><a name="testConnectionOnCheckin" />testConnectionOnCheckin</dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
If true, an operation will be performed asynchronously at every connection checkin to verify that the connection is valid.
Use in combination with <tt>idleConnectionTestPeriod</tt> for quite reliable, always asynchronous Connection testing.
Also, setting an <tt>automaticTestTable</tt> or <tt>preferredTestQuery</tt> will usually speed up all connection tests.
[See <a href="#configuring_connection_testing">"Configuring Connection Testing"</a>]
</div>
</dd>
<dt><a name="testConnectionOnCheckout" />testConnectionOnCheckout</dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
<b><i>Use only if necessary. Expensive.</i></b>
If true, an operation will be performed at every connection checkout to verify that the connection is valid.
<b>Better choice:</b> verify connections periodically using <tt>idleConnectionTestPeriod</tt>. Also, setting an
<tt>automaticTestTable</tt> or <tt>preferredTestQuery</tt> will usually speed up all connection tests.
[See <a href="#configuring_connection_testing">"Configuring Connection Testing"</a>]
</div>
</dd>
<dt><a name="unreturnedConnectionTimeout" />unreturnedConnectionTimeout</dt>
<dd>
<div class="default">Default: 0</div>
<div class="propdesc">
Seconds. If set, if an application checks out but then fails to check-in [i.e. close()] a Connection
within the specified period of time, the pool will unceremoniously destroy() the Connection. This permits
applications with occasional Connection leaks to survive, rather than eventually exhausting the Connection
pool. And that's a shame. Zero means no timeout, applications are expected to close() their own Connections.
Obviously, if a non-zero value is set, it should be to a value longer than any Connection should reasonably
be checked-out. Otherwise, the pool will occasionally kill Connections in active use, which is bad.
<b><i>This is basically a bad idea, but it's a commonly requested feature. Fix your $%!@% applications
so they don't leak Connections! Use this temporarily in combination with
<tt>debugUnreturnedConnectionStackTraces</tt> to figure out
where Connections are being checked-out that don't make it back into the pool!</i></b>
[See <a href="#configuring_to_debug_and_workaround_broken_clients">"Configuring to Debug and Workaround Broken Client Applications"</a>]
</div>
</dd>
<dt><a name="user" />user</dt>
<dd>
<div class="default">Default: null</div>
<div class="propdesc">
For applications using <tt>ComboPooledDataSource</tt> or any
c3p0-implemented unpooled DataSources — <tt>DriverManagerDataSource</tt> or the
DataSource returned by <tt>DataSources.unpooledDataSource()</tt> —
defines the username that will be used for the DataSource's default
<tt>getConnection()</tt> method. (See also <a href="#password">password</a>.)
</div>
<div class="per-user">Does Not Support Per-User Overrides.</div>
<dt><a name="usesTraditionalReflectiveProxies" /><s>usesTraditionalReflectiveProxies</s></dt>
<dd>
<div class="default">Default: false</div>
<div class="propdesc">
<span class="deprecated">Deprecated.</span> c3p0 originally used reflective dynamic proxies for
implementations of Connections and other JDBC
interfaces. As of c3p0-0.8.5, non-reflective, code-generated implementations are used instead. As
this was a major change, and the old codebase had been extensively used and tested, this parameter
was added to allow users to revert of they had problems. The new, non-reflexive implementation is
faster, and has now been widely deployed and tested, so it is unlikely that this parameter will be useful.
Both the old reflective and newer non-reflective codebases are being maintained, but support for the
older codebase may (or may not) be dropped in the future.
</div>
</dd>
</dl>
<h3>
<a name="other-properties">Other Properties</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
The following configuration properties affect the behavior of the c3p0 library as a whole. They
may be set as system properties, or in a <a href="#c3p0_properties"><tt>c3p0.properties</tt></a> file.
</p>
<div class="other_properties_desc">
<h4><a name="locating_configuration_information">Locating Configuration Information</a></h4>
<p>
Normally, c3p0's configuration information is placed in a either a c3p0-config.xml or c3p0.properties file
at the top-level of an application's CLASSPATH. However, if you wish to place configuration information
elsewhere, you may place c3p0 configuration information (in the <a href="#c3p0-config.xml">XML file format</a> only!) anywhere you'd like
in the filesystem visible to your application. Just set the following property to the full, absolute path
of the XML config file:
</p>
<ul class="other_props_list">
<li>com.mchange.v2.c3p0.cfg.xml</li>
</ul>
<p>
If you set this property to a value beginning with "<tt>classloader:</tt>", c3p0 will search for an XML config file as a ClassLoader resource,
that is, in any location you specify under your classpath, including jar-file <tt>META-INF</tt> directories.
</p>
<h4>Logging-related properties</h4>
<p>
The following properties affect c3p0's logging behavior. Please see <a href="#configuring_logging">Configuring Logging</a>
above for specific information.
</p>
<ul class="other_props_list">
<li>com.mchange.v2.log.MLog</li>
<li>com.mchange.v2.log.NameTransformer</li>
<li>com.mchange.v2.log.FallbackMLog.DEFAULT_CUTOFF_LEVEL</li>
</ul>
<h4>Configuring JMX</h4>
<p>
The following property controls c3p0's JMX management interface. Plese see
<a href="#jmx_configuration_and_management">Configuring and Managing c3p0 via JMX</a> above
for more information.
</p>
<ul class="other_props_list">
<li>com.mchange.v2.c3p0.management.ManagementCoordinator</li>
</ul>
<h4>Configuring the VMID</h4>
<p>
Is it better to be beautiful or correct? Beginning with c3p0-0.9.1, c3p0 opts somewhat reluctantly for correctness.
</p>
<p>
Here's the deal. Every c3p0 DataSource is allocated a unique "identity token", which is used to ensure that multiple
JNDI lookups of the same PooledDataSource always return the same instance, even if the JNDI name-server stores a
Serialized or Referenced instance. Previously, c3p0 was happy for generated IDs to be unique within a single VM (and it
didn't even get that quite right, before c3p0-0.9.1). But in theory, one VM might look up two different DataSources,
generated by two different VMs, that by unlikely coincidence have the same "identity token", leading to errors as one
of the two DataSources sneakily substitutes for the second. Though this hypothetical issue has never been reported in practice,
c3p0 resolves it by prepending a VMID to its identity tokens. This makes them long and ugly, but correct.
</p>
<p>
If you don't like the long and ugly VMID, you can set your own, or you can turn off this solution to a hypothetical
non-problem entirely with the following property:
</p>
<ul class="other_props_list">
<li>com.mchange.v2.c3p0.VMID</li>
</ul>
<p>
Set it to <tt>NONE</tt> to turn off the VMID, set it to <tt>AUTO</tt> to let c3p0 generate a VMID,
or provide any other String to set the VMID that will be used directly. The default is <tt>AUTO</tt>.
</p>
<h4>Experimental properties</h4>
<p>
c3p0-0.9.1 includes a new implementation of asynchronous Connection acquisition that
should improve c3p0's performance and resource utilization in cases where database
acquisition attempts, for whatever reason, occasionally fail. The new implementation
should be significantly better than the "traditional" Connection acquisition strategy,
but was added too late in the c3p0-0.9.1 development cycle to be fully tested and
enabled by default. Users are encouraged to try the new implementation, both because
it is better, and to help iron out any unanticipated problems.
</p>
<p>
For a full description of the new implementation and the resource bottleneck it is
designed to overcome, please see the <tt>CHANGELOG</tt> entry for <tt>c3p0-0.9.1-pre11</tt>.
</p>
<p>
As of c3p0-0.9.2 this feature is enabled by default. To revert to the traditional Connection
acquisition behavior, set the following parameter to <tt>false</tt>.
</p>
<ul class="other_props_list">
<li>com.mchange.v2.resourcepool.experimental.useScatteredAcquireTask</li>
</ul>
</div>
</div>
<hr/>
<h2>
<a name="configuration_files">Appendix B: Configuration Files, etc.</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h2>
<div class="sectiontext">
<p>
c3p0 configuration parameters can be set
<a href="#programmatic_configuration">directly in Java code</a>,
via a <a href="#c3p0_properties">simple Java properties file</a>,
via an <a href="#c3p0-config.xml">XML configuration file</a>, or
via <a href="#system_properties">System properties</a>.
Any which way
works (the the XML configuration is most powerful, though, as it supports multiple named configurations and
per-user overrides. Choose whatever works best for you.
</p>
<h3>
<a name="c3p0_properties">Overriding c3p0 defaults via <tt>c3p0.properties</tt></a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
To override the library's built-in defaults, create a file called <tt>c3p0.properties</tt>
and place it at the "root" of your classpath or classloader. For a typical standalone
application, that means place the file in a directory named in your <tt>CLASSPATH</tt>
environment variable. For a typical web-application, the file should be placed in
<tt>WEB-INF/classes</tt>. In general, the file must be available as a classloader
resource under the name <tt>/c3p0.properties</tt>, in the classloader that loaded
c3p0's jar file. Review the API docs (especilly <tt>getResource...</tt> methods) of
<tt>java.lang.Class</tt>, <tt>java.lang.ClassLoader</tt>, and <tt>java.util.ResourceBundle</tt>
if this is unfamiliar.
</p>
<p>
The format of <tt>c3p0.properties</tt> should be a normal Java Properties file format,
whose keys are c3p0 configurable properties. See <a href="#configuration_properties">Appendix A</a>.
for the specifics. An example <tt>c3p0.properties</tt> file is produced below:
</p>
<div class="example">
# turn on statement pooling
c3p0.maxStatements=150
# close pooled Connections that go unused for
# more than half an hour
c3p0.maxIdleTime=1800
</div>
<h3>
<a name="system_properties">Overriding c3p0 defaults with System properties</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 properties can also be defined as System properties, using the same "c3p0." prefix for properties
specified in a <tt>c3p0.properties</tt> file.
</p>
<div class="example">
swaldman% java -Dc3p0.maxStatements=150 -Dc3p0.maxIdleTime=1800 example.MyC3P0App
</div>
<p>
System properties override settings in c3p0.properties. Please see
<a href="#configuration_precedence">Precedence of Configuration Settings</a> for more information.
</p>
<h3>
<a name="c3p0-config.xml">Named and Per-User configuration: Overriding c3p0 defaults via <tt>c3p0-config.xml</tt></a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
As of c3p0-0.9.1, you can define multiple configurations in an XML configuration file, and specify in your code which
configuration to use. For any configurations (including the unnamed default configuration), you can define overrides
for a particular database user. For example, if several applications access your database under different authentication
credentials, you might define <tt>maxPoolSize</tt> to be 100 for user <tt>highVolumeApp</tt>, but only 10 for user
<tt>lowLoadApp</tt>. (Recall that Connections associated with different authentication credentials
are of necessity separated into separate pools, so it makes sense that these could be configured separately.)
</p>
<p>
You can use the XML config file for all c3p0 configuration, including configuration of defaults. However, for users who
don't want or need the extra complexity, the c3p0.properties file will continue to be supported.
</p>
<p>
By default, c3p0 will look for an XML configuration file in its classloader's resource path under the name "/c3p0-config.xml".
That means the XML file should be placed in a directly or jar file directly named in your applications CLASSPATH, in WEB-INF/classes,
or some similar location.
</p>
<p>
If you prefer not to bundle your configuration with your code, you can specify an ordinary filesystem location for c3p0's
configuration file via the system property <tt>com.mchange.v2.c3p0.cfg.xml</tt>. (You can also use this property to specify an
alternative location in the ClassLoader resource path, e.g. <tt>META-INF</tt>. See <a href="#locating_configuration_information">Locating Configuration Information</a>.)
</p>
<p>
Here is an example <tt>c3p0-config.xml</tt> file:
</p>
<div class="example">
<c3p0-config>
<default-config>
<property name="automaticTestTable">con_test</property>
<property name="checkoutTimeout">30000</property>
<property name="idleConnectionTestPeriod">30</property>
<property name="initialPoolSize">10</property>
<property name="maxIdleTime">30</property>
<property name="maxPoolSize">100</property>
<property name="minPoolSize">10</property>
<property name="maxStatements">200</property>
<user-overrides user="test-user">
<property name="maxPoolSize">10</property>
<property name="minPoolSize">1</property>
<property name="maxStatements">0</property>
</user-overrides>
</default-config>
<!-- This app is massive! -->
<named-config name="intergalactoApp">
<property name="acquireIncrement">50</property>
<property name="initialPoolSize">100</property>
<property name="minPoolSize">50</property>
<property name="maxPoolSize">1000</property>
<!-- intergalactoApp adopts a different approach to configuring statement caching -->
<property name="maxStatements">0</property>
<property name="maxStatementsPerConnection">5</property>
<!-- he's important, but there's only one of him -->
<user-overrides user="master-of-the-universe">
<property name="acquireIncrement">1</property>
<property name="initialPoolSize">1</property>
<property name="minPoolSize">1</property>
<property name="maxPoolSize">5</property>
<property name="maxStatementsPerConnection">50</property>
</user-overrides>
</named-config>
</c3p0-config>
</div>
<p>
To use a named configuration, you specify the config name when creating your DataSource. For example, using
<a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html"><tt>ComboPooledDataSource</tt></a>:
</p>
<div class="example">
ComboPooledDataSource cpds = new ComboPooledDataSource("intergalactoApp");
</div>
<p>
Or using the
<a href="apidocs/com/mchange/v2/c3p0/DataSources.html"><tt>DataSources</tt></a> factory class:
</p>
<div class="example">
DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled, "intergalactoApp" );
</div>
<!--
<h3>
<a name="programmatic_configuration">Programmatic configuration of DataSource instances</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
-->
<h3>
<a name="configuration_precedence">Precedence of Configuration Settings</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h3>
<p>
c3p0 now permits configuration parameters to be set in a number of different ways and places. Fortunately,
there is a clear order of precedence that determines which configuration will "take" in the event of conflicting
settings. Conceptually, c3p0 goes down this list from top to bottom, using the first setting it finds.
</p>
<p>
Most applications will never use per-user or named configurations. For these applications, we
present a simplified precedence hierarchy:
</p>
<div align="center">
<ol class="precedence">
<li>Configuration values programmatically set.</li>
<li>System property setting of configuration value.</li>
<li>Configuration values taken from the default configuration of a <tt>c3p0-config.xml</tt> file.</li>
<li>Configuration values specified in a <tt>c3p0.properties</tt> file</li>
<li>c3p0's hard-coded default values.</li>
</ol>
</div>
<p>
For applications that do use named and per-user configurations, here is the complete, normative precedence hierarchy:
</p>
<div align="center">
<ol class="precedence">
<li>
User-specific overrides programmatically set via:
<ul>
<li><a href="apidocs/com/mchange/v2/c3p0/ComboPooledDataSource.html#setUserOverridesAsString"><tt>ComboPooledDataSource.setUserOverridesAsString()</tt></a></li>
<li><a href="apidocs/com/mchange/v2/c3p0/WrapperConnectionPoolDataSource.html#setUserOverridesAsString"><tt>WrapperConnectionPoolDataSource.setUserOverridesAsString()</tt></a></li>
</ul>
Note that programmatically setting user-specific overrides <u>replaces</u> all user-specific configuration taken from
other sources. If you want to merge programmatic changes with preconfigured overrides, you'll have to use <tt>getUserOverridesAsString()</tt>
and modify the original settings before replacing.
</li>
<li>User-specific overrides taken from a DataSource's named configuration (specified in <tt>c3p0-config.xml</tt>)</li>
<li>User-specific overrides taken from the default configuration (specified in <tt>c3p0-config.xml</tt>)</li>
<li>Non-user-specific values programmatically set.</li>
<li>Non-user-specific values taken from a DataSource's named configuration (specified in <tt>c3p0-config.xml</tt>)</li>
<li>System property setting of configuration value.</li>
<li>Non-user-specific values taken from the default configuration (specified in <tt>c3p0-config.xml</tt>)</li>
<li>Values specified in a <tt>c3p0.properties</tt> file</li>
<li>c3p0's hard-coded default values.</li>
</ol>
</div>
</div>
<h2>
<a name="hibernate-specific">Appendix C: Hibernate-specific notes</a>
<span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span>
</h2>
<div class="sectiontext">
<p>
Hibernate's C3P0ConnectionProvider renames 7 c3p0 configuration properties, which, if set in your hibernate
configuration, <b>will override</b> any configuration you may have set in a <tt>c3p0.properties</tt> file:
</p>
<div class="hibernate_props">
<table class="hibernate_props">
<tr>
<th>c3p0-native property name</th><th>hibernate configuration key</th>
</tr>
<tr>
<td>c3p0.acquireIncrement</td><td>hibernate.c3p0.acquire_increment</td>
</tr>
<tr>
<td>c3p0.idleConnectionTestPeriod</td><td>hibernate.c3p0.idle_test_period</td>
</tr>
<tr>
<td>c3p0.initialPoolSize</td><td><span class="hibparam_comment">not available -- uses minimum size</span></td>
</tr>
<tr>
<td>c3p0.maxIdleTime</td><td>hibernate.c3p0.timeout</td>
</tr>
<tr>
<td>c3p0.maxPoolSize</td><td>hibernate.c3p0.max_size</td>
</tr>
<tr>
<td>c3p0.maxStatements</td><td>hibernate.c3p0.max_statements</td>
</tr>
<tr>
<td>c3p0.minPoolSize</td><td>hibernate.c3p0.min_size</td>
</tr>
<tr>
<td>c3p0.testConnectionsOnCheckout </td><td>hibernate.c3p0.validate <span class="hibparam_comment">hibernate 2.x only!</span></td>
</tr>
</table>
</div>
<p>
You can set any c3p0 properties in your hibernate config using the prefix <tt>hibernate.c3p0</tt>. For example
</p>
<div class="example">
hibernate.c3p0.unreturnedConnectionTimeout=30
hibernate.c3p0.debugUnreturnedConnectionStackTraces=true
</div>
<p>
might be set to help <a href="#configuring_to_debug_and_workaround_broken_clients">debug Connection leaks</a>.
</p>
<p>
You can always set c3p0 config in a <tt>c3p0.properties</tt> or <tt>c3p0-config.xml</tt> file
(see <a href="#c3p0_properties">"Overriding c3p0 defaults via c3p0.properties"</a>, <a href="#c3p0-config.xml">"Overriding c3p0 defaults via c3p0-config.xml"</a>),
but <i><u>any configuration set in Hibernate config files will override c3p0-native configuation!</u></i>
</p>
</div>
<hr/>
<h2><a name="tomcat-specific">Appendix D: Configuring c3p0 DataSources in Tomcat</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
You can easily configure Apache's Tomcat web application server to use c3p0 pooled DataSources.
Below is a Tomcat 5.0 sample config to get you started. It's a fragment of Tomcat's <tt>conf/server.xml</tt> file,
which should be modified to suit and placed inside a <tt><Context></tt> element.
</p>
<div class="example">
<Resource name="jdbc/pooledDS" auth="Container" type="com.mchange.v2.c3p0.ComboPooledDataSource" />
<ResourceParams name="jdbc/pooledDS">
<parameter>
<name>factory</name>
<value>org.apache.naming.factory.BeanFactory</value>
</parameter>
<parameter>
<name>driverClass</name>
<value>org.postgresql.Driver</value>
</parameter>
<parameter>
<name>jdbcUrl</name>
<value>jdbc:postgresql://localhost/c3p0-test</value>
</parameter>
<parameter>
<name>user</name>
<value>swaldman</value>
</parameter>
<parameter>
<name>password</name>
<value>test</value>
</parameter>
<parameter>
<name>minPoolSize</name>
<value>5</value>
</parameter>
<parameter>
<name>maxPoolSize</name>
<value>15</value>
</parameter>
<parameter>
<name>acquireIncrement</name>
<value>5</value>
</parameter>
</ResourceParams>
</div>
<p>For Tomcat 5.5, try something like the following (thanks to Carl F. Hall for the sample!):</p>
<div class="example">
<Resource auth="Container"
description="DB Connection"
driverClass="com.mysql.jdbc.Driver"
maxPoolSize="4"
minPoolSize="2"
acquireIncrement="1"
name="jdbc/TestDB"
user="test"
password="ready2go"
factory="org.apache.naming.factory.BeanFactory"
type="com.mchange.v2.c3p0.ComboPooledDataSource"
jdbcUrl="jdbc:mysql://localhost:3306/test?autoReconnect=true" />
</div>
<p>
The rest is standard J2EE stuff: You'll need to declare your DataSource reference in your <tt>web.xml</tt>
file:
</p>
<div class="example">
<resource-ref>
<res-ref-name>jdbc/pooledDS</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</div>
<p>
And you can access your DataSource from code within your web application like this:
</p>
<div class="example">
InitialContext ic = new InitialContext();
DataSource ds = (DataSource) ic.lookup("java:comp/env/jdbc/pooledDS");
</div>
<p>
That's it!
</p>
</div>
<hr/>
<h2><a name="jboss-specific">Appendix E: JBoss-specific notes</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
To use c3p0 with JBoss:
<ol>
<li>
Place c3p0's jar file in the <tt>lib</tt> directory of your
jboss server instance (e.g. <tt>${JBOSS_HOME}/server/default/lib</tt>)
</li>
<li>
Modify the file below, and save it as <tt>c3p0-service.xml</tt> in the
<tt>deploy</tt> directory of your jboss server (e.g. <tt>${JBOSS_HOME}/server/default/deploy</tt>).
Note that parameters must be capitalized in this file, but otherwise they are defined as described
above.
</li>
</ol>
<p>
<div id="showDeprecatedJbossConfigName" style="display: block">
<b>Note:</b> <a href="#" onClick="return toggleDisplay('showDeprecatedJbossConfigName', 'DeprecatedJbossConfigName');">
Users of c3p0 jboss support prior to c3p0-0.9.1 please click here!</a>
</div>
</p>
<div class="deprecated" id="DeprecatedJbossConfigName">
<p>
<b>Please note: As of c3p0-0.9.1, the class name of the jboss configuration mbean has changed
to <tt>com.mchange.v2.c3p0.jboss.C3P0PooledDataSource</tt> (from <tt>com.mchange.v2.c3p0.mbean.C3P0PooledDataSource</tt>),
in order to distinguish what is really jboss-specific functionality from c3p0's more general JMX
support.</b>
</p>
<p>
The old jboss config mbeans are deprecated, but will still work. However, support for new configuration
parameters will only be added under the new name. Updating requires a one-word change to your <tt>c3p0-service.xml</tt>,
change "mbean" to "jboss" where your old file says 'code="com.mchange.v2.c3p0.mbean.C3P0PooledDataSource"'. Just do it!
</p>
<p>
<a id="hideDataSourcesWithPoolConfig"
href="#"
onClick="return toggleDisplay('showDeprecatedJbossConfigName', 'DeprecatedJbossConfigName');"
>Hide box.</a>
<p>
</div>
</div>
<div class="example">
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE server>
<server>
<mbean code="com.mchange.v2.c3p0.jboss.C3P0PooledDataSource"
name="jboss:service=C3P0PooledDataSource">
<attribute name="JndiName">java:PooledDS</attribute>
<attribute name="JdbcUrl">jdbc:postgresql://localhost/c3p0-test</attribute>
<attribute name="DriverClass">org.postgresql.Driver</attribute>
<attribute name="User">swaldman</attribute>
<attribute name="Password">test</attribute>
<!-- Uncomment and set any of the optional parameters below -->
<!-- See c3p0's docs for more info. -->
<!-- <attribute name="AcquireIncrement">3</attribute> -->
<!-- <attribute name="AcquireRetryAttempts">30</attribute> -->
<!-- <attribute name="AcquireRetryDelay">1000</attribute> -->
<!-- <attribute name="AutoCommitOnClose">false</attribute> -->
<!-- <attribute name="AutomaticTestTable"></attribute> -->
<!-- <attribute name="BreakAfterAcquireFailure">false</attribute> -->
<!-- <attribute name="CheckoutTimeout">0</attribute> -->
<!-- <attribute name="ConnectionCustomizerClassName"></attribute> -->
<!-- <attribute name="ConnectionTesterClassName"></attribute> -->
<!-- <attribute name="Description">A pooled c3p0 DataSource</attribute> -->
<!-- <attribute name="DebugUnreturnedConnectionStackTraces">false</attribute> -->
<!-- <attribute name="FactoryClassLocation"></attribute> -->
<!-- <attribute name="ForceIgnoreUnresolvedTransactions">false</attribute> -->
<!-- <attribute name="IdleConnectionTestPeriod">0</attribute> -->
<!-- <attribute name="InitialPoolSize">3</attribute> -->
<!-- <attribute name="MaxAdministrativeTaskTime">0</attribute> -->
<!-- <attribute name="MaxConnectionAge">0</attribute> -->
<!-- <attribute name="MaxIdleTime">0</attribute> -->
<!-- <attribute name="MaxIdleTimeExcessConnections">0</attribute> -->
<!-- <attribute name="MaxPoolSize">15</attribute> -->
<!-- <attribute name="MaxStatements">0</attribute> -->
<!-- <attribute name="MaxStatementsPerConnection">0</attribute> -->
<!-- <attribute name="MinPoolSize">0</attribute> -->
<!-- <attribute name="NumHelperThreads">3</attribute> -->
<!-- <attribute name="PreferredTestQuery"></attribute> -->
<!-- <attribute name="TestConnectionOnCheckin">false</attribute> -->
<!-- <attribute name="TestConnectionOnCheckout">false</attribute> -->
<!-- <attribute name="UnreturnedConnectionTimeout">0</attribute> -->
<!-- <attribute name="UsesTraditionalReflectiveProxies">false</attribute> -->
<depends>jboss:service=Naming</depends>
</mbean>
</server>
</div>
</p>
</div>
<hr/>
<h2><a name="oracle-specific">Appendix F: Oracle-specific API: createTemporaryBLOB() and createTemporaryCLOB()</a><span class="toplink"><a href="#contents"><img src="arrow_sm.png" width="20" alt="Go To Top"/></a></span></h2>
<div class="sectiontext">
<p>
The Oracle thin JDBC driver provides a non-standard API for creating temporary BLOBs and CLOBs that
requires users to call methods on the raw, Oracle-specific Connection implementation. Advanced users
might use the <a href="#raw_connection_ops">raw connection operations</a> described above to access this
functionality, but a convenience class is available in a separate jar file (<tt>c3p0-oracle-thin-extras-@c3p0.version@.jar</tt>)
for easier access to this functionality. Please see the
<a href="apidocs-oracle-thin/index.html">API docs for <tt>com.mchange.v2.c3p0.dbms.OracleUtils</tt></a>
for details.
</p>
</div>
<hr/>
<a href="#contents">Back to Contents</a>
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