I was getting error, Unable to load performance pack. Using Java I/O instead. when using weblogic on SunOS for JMS. JMS was slow, found solution for that here.
But what I am unable to understand is, what is this performance pack exactly? And how could it affect JMS publish rate?
Weblogic makes use of a set of native files for Disk I/O, these are generally faster than using the standard Java I/O. These native library files are packaged within your WLS installation and your startup script picks the appropriate one based on your configuration (ie 32/64 bit).
Check which file its trying to load and failing, see if the file is there in the correct location, and make appropriate changes to your startup script so wls can pick the file properly, a restart is required for the change to take effect.