Tomcat - maxThreads vs. maxConnections
java, tomcat
Solution
Tomcat can work in 2 modes:
- BIO – blocking I/O (one thread per connection)
- NIO – non-blocking I/O (many more connections than threads)
Tomcat 7 is BIO by default, although consensus seems to be "don't use BIO because NIO is better in every way". (And BIO has been completely thrown out of 8.5.0 and later versions.) You set this using the `protocol` parameter in the `server.xml` file.
- BIO will be `HTTP/1.1` or `org.apache.coyote.http11.Http11Protocol`
- NIO will be `org.apache.coyote.http11.Http11NioProtocol`
If you're using BIO then I believe they should be more or less the same.
If you're using NIO then actually "maxConnections=1000" and "maxThreads=10" might even be reasonable. The defaults are maxConnections=10,000 and maxThreads=200. With NIO, each thread can serve any number of connections, switching back and forth but retaining the connection so you don't need to do all the usual handshaking which is especially time-consuming with HTTPS but even an issue with HTTP. You can adjust the "keepAlive" parameter to keep connections around for longer and this should speed everything up.
Problem
In Tomcat's `server.xml` what is `maxThreads` versus `maxConnections`? I understand that `maxConnections` is the number of connections open to the server. And `maxThreads` is the maximum number of request processing threads . But how do these two configuration parameters work together? -- Obviously you will not set `maxConnections` to 1000 and `maxThreads` to 10. What is the relationship between the two configuration parameters? ``` <Connector port="8443" protocol="org.apache.coyote.http11.Http11Protocol" maxThreads="250" SSLEnabled="true" scheme="https" secure="true" clientAuth="false" sslProtocol="TLS" connectiontimeout="20000" /> ```