PHP Acceleration is caching of the compiled PHP script in memory. This is highly recommended when running eZ publish it will really boost the performance of your eZ publish site.

Collection of documents touching the optimization of eZ publish 3.

Execution speed increases a lot if you use the free Alternativ PHP Cache, ionCube php accelerator or Turck MMCache.

IonCube can improve response times from the server by upto 80%, but make sure you check your php.ini as it requires more memory and if your memory limit is too low this will cause script errors.
A good general setting for ionCude php accelerator is (in php.ini).

zend_extension=/usr/lib/php4/php_accelerator_1.3.3r2.so

phpa.shm_ttl = 6h

phpa.shm_size = 15

Its probably worth checking you /tmp directory to ensure you have enough space for all those files the accelerator creates.

If your memory gets out of control as it does on standard Redhat 7.3 installs then you need the memory workaround

phpa.enable_php_memory_bug_workaround = 1

ionCube is a good solid "free" solution when speeding up php and has been run by some community members for months without problem. It has been known to have problems on PHP 4.1.2 when you host many sites, ensure you test it fully before deploying 10 sites+ on a box with this accelerator.

An even better but expensive option (490+ USD) is the Zend Performance Suite

Other options include compiling PHP to remove unwanted modules, this will reduce the size of the executed code.

You might also consider building your own Apache for the use in combination of eZ publish.