Tomcat - Configuring maxThreads and acceptCount in Http connector

Question

I currently have an application deployed using Tomcat that interacts with a Postgres database via JDBC. The queries are very expensive, so what I'm seeing is a timeout caused by Tomcat or Apache (Apache sits in front of Tomcat in my configuration). I'm trying to limit the connections to the database to 20-30 simultaneous connections, so that the database is not overwhelmed. I've done this using the \.. configuration, setting maxActive to 30 and maxIdle to 20. I also bumped up the maxWait.

In this scenario I'm limiting the USE of the database, but I want the connections/requests to be POOLED within Tomcat. Apache can accept 250 simultaneous requests. So I need to ensure Tomcat can also accept this many, but handle them appropriately.

Tomcat has two settings in the HTTP Connector config file:

• maxThreads - "Max number of request processing threads to be created by the Http Connector, which therefore determines the max number of simultaneous requests that can be handled."
• acceptCount - "The maximum queue length for incoming connection requests when all possible request processing threads are in use. Any requests received when the queue is full will be refused."

So I'm guessing that if I set maxThreads to the max number of JDBC connections (30), then I can set acceptCount to 250-30 = 220.

I don't quite understand the difference between a thread that is WAITING on a JDBC connection to open up from the pool, versus a thread that is queued... My thought is that a queued thread is consuming less cycles whereas a running thread, waiting on the JDBC pool, will be spending cycles checking the pool for a free thread...?

Solution

Note that the HTTP connector is for incoming HTTP requests, and unrelated to JDBC. You probably want to configure the JDBC connection pool separately, such as the connectionProperties for the JDBC connector: http://tomcat.apache.org/tomcat-7.0-doc/jdbc-pool.html