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DBCP Overview

Commons-DBCP provides database connection pooling services.

A lot of information is available on the [http://jakarta.apache.org/commons/dbcp/ DBCP website]. If you don't find the information you need you can always contact us using one of the [http://jakarta.apache.org/site/mail2.html#Commons mailing lists].

External Resources

Here's a little diagram showing what datastructure DBCP sets up and how that datastructure is used in case the DriverManager is employed to obtain Drivers at runtime. Please send any corrections (for now) to d.tonhofer@m-plify.com.

  • [http://rei1.m-plify.net/Apache_DBCP/Apache_DBCP_Structure.pdf Apache_DBCP_Structure.pdf]

  • [http://rei1.m-plify.net/Apache_DBCP/Apache_DBCP_Structure.vsd Apache_DBCP_Structure.vsd]

  • [http://rei1.m-plify.net/Apache_DBCP/Apache_DBCP_Structure.png Apache_DBCP_Structure.png]

Diagrams hosted by http://rei1.m-plify.net

FAQ

Q: Is this project still active or have they just not released anything in an excessive period of time?

A: DBCP is still active. We don't do a lot of releases but

Q: What is the best way, ASIDE from running a query against the DB, to be sure that the connection is still valid when it is retrieved from the pool?

A: How would you do this without a pool? I.e., what is the best way aside from running a query to be sure that a connection is still valid when returned from DriverManager DataSource.getConnection?

When upgrading from DBCP 1.0 to DBCP 1.1 you can encounter the following issue (reported on commons-user):

We are accessing mainframe data using a JDBC driver, but it is not truly a database. Specifically, the setAutoCommit and setReadOnly Connection methods fail. Version 1.0 of DBCP silently discarded these errors and allowed the connections to be created and used anyway. Version 1.1 of activateObject surfaces these exceptions and fails to create new connections in the pool. (solution: use custom activateObject method)

Q: I see in the javadocs that AbandonedConnectionPool was deprecated (DBCP 1.1). What replaced it?

A: The original reason for deprecation was the danger in reusing a abandoned connection without knowing if it is safe to do so. There was a discussion about it in april. Some people wanted to remove it completely.

I took a different approach. In 1.1 an abandoned connection will not be reused but closed (and a new one created). The classes remained deprecated because I think the AbandonedPool should move to the pool package (and made more generic/safe).

The abandoned connection feature on BasicDataSource will remain supported in one form or another. I'm not using it on my tomcat production configurations but there are junit tests to make sure everything works.

So if you are using the Abandoned* classes directly then it is possible you are affected by a future refactoring (we will try to remain compatible if possible of course). If you use BasicDataSource then you can be sure the feature will remain.

Q: When using DBCP what parameter needs to be set on the ObjectPool so that a minimum number of connections are created when the pool instance is created ? I thought the setMinIdle() does this, but doesn't look so.

A: You can setMinIdle() to always have a minimum amount of idle connection in the pool. (not only at the start of the pool but the whole time) The minIdle check is done in the evictor thread so timeBetweenEvictionRunsMillis has to be set to a non negative-value. (you can optionally turn off the eviction by setting numTestsPerEvictionRun to zero or just set minEvictableIdleTimeMillis very high).

A more simple way to create a number of connections at startup is to use the pool.addObject() method. (add the following after creating the PoolableConnectionFactory)

for (int i=0 ; i<initialsize ; i++) {
   connectionPool.addObject()
}

Q: <nowiki>Does the current 1.1 release support the poolable/caching of PreparedStatements. I noted that the PoolableConnectionFactory can take a KeyedObjectPoolFactory as a statement pool factory. But there is not concrete implementation for the KeyedPoolableObjectFactory which is required when creating a GenericKeyedObjectPoolFactory. If I pass in a null as shown in the examples, does it cache prepared statements or should I do that in local objects?</nowiki>

A: ??

Q: Where do I get a concrete example of PerUserPoolDataSource? How do we use it in a situation where multiple pools are required for different modules of a project and their properties differ on the database transactional load?

Q: Can DBCP be compiled with JDK1.3?

A: The ant build has facilities to comment out the JDBC3 method making DBCP source compatible with JDK1.3. DBCP1.2 had some JDK1.4 method but those were removed, see issue 29454.

Q: 'Uh'... what about PoolableConnectionFactory line 51 & others which use Boolean.valueOf(boolean) which was introduced in 1.4?

A: They were replaced: http://cvs.apache.org/viewcvs.cgi/jakarta-commons/dbcp/src/java/org/apache/commons/dbcp/PoolableConnectionFactory.java?r1=1.22&r2=1.23&diff_format=h

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