Understanding the Apache Tomcat blocking IO connector

posted by SpringSource on October 27, 2009 02:24 PM

Why active threads remain high after load decreases using the Blocking IO connector

There are a number of different http connectors that can be used with Tomcat. They are:

• Blocking IO
• Non-blocking IO
• Native/Apache Portable Runtime (APR)

The blocking IO connector is the default http connector. With this connector each request is handled by a dedicated thread (obtained from a pool) until the request is complete at which point the thread is returned to the pool to be re-used by another request.

The difference between the connectors are described at the end of the following document as provided by the Apache Server Foundation: http://tomcat.apache.org/tomcat-6.0-doc/config/http.html

The thread pool used by the blocking IO connector will increase in size but never decrease. Not reducing the thread pool size reduces complexity and gives a slight performance improvement at the cost of increased resource usage during periods of light load.

The blocking IO connector is recommended over the other connectors for:

• stability
• non-SSL
• performance if keep-alive is disabled (it is in your configuration)

If you were using SSL and/or keep-alive and not running on Solaris then the APR connector would be preferred. If you were using SSL and/or keep-alive on Solaris then NIO would be preferred.

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