performance

When facing problems regarding memory consumption of a Java application, the JDK contains a number of useful tools to help you understand what is going on. You can get a list of the tools on this page.
One of these tools is "jmap". Jmap will let you now (among other things) know what objects are using your precious memory.

Cool!
...
except that when you try to use jmap on Ubuntu 11.04 with a Sun JVM 6, you will get this error message:

Attaching to process ID 12450, please wait...

We have been running a Red5 server for quite some time, and as our application was getting more popular, we happened to see new errors we had never seen before. Actually, we saw a bunch of "Too many open files" exceptions in the logs, and most users could not connect anymore to our application.

In this article, I will explain how to install the APC opcode cache in a few easy steps, on Ubuntu 10.04.
APC is an opcode cache (and more). When a PHP script is run, it is compiled by PHP internally, before executing it. PHP does not store the compiled result, therefore, next time the script is run, PHP will compile it again. APC is designed to store the result in its cache. This way, when PHP executes again a script, APC will serve the compiled script from the cache. PHP won't have to parse the script again, and it will save a lot of time.

First step: install PECL