Overview

A zAAP is a relatively new type of technology introduced by IBM to address the software licencing costs associated with running Java on the zOS operating system. A zAAP (formerly known as an IFA) is a co-processor which can be added to a z890 or z990 system and can only run Java. Any cycles on the zAAP are not counted towards the MIPS used for software license calculations. A zAAP is also significantly less expensive than a conventional mainframe engine.

Limitations

Since a zAAP is a co-processor, you can only purchase as many zAAPs as conventional engines. Also, since the zAAP cannot be dispatched to directly from zOS, you need to have enough conventional engines in the system to be able to dispatch work to the zAAP. Otherwise, the zAAP could be starved. There are zOS parameters that control how work is dispatched to the zAAP. For example, if you set CROSSOVER=YES, new work will be dispatched to the first available processor, zAAP or conventional. If you set CROSSOVER=NO, the work will be queued up until a zAAP becomes available. So, you have to decide whether your throughput or cost is a higher priority. Not all of the Java workload can run on the zAAP. Certain parts of the code, especially native methods need to run on conventional engines. The latest numbers from IBM show that typically about 70% of the Java CPU cycles can run on a zAAP. The 1.4.x JVMs from IBM offer a set of parameters which allow you to generate predictions of how much of the zAAP your code will utilize. Your mileage will vary! zAAPs can be utilized only under zOS 1.6 or higher.