We haven't done much with Java in the last few years, but our experience
with mission-critical production Java apps on z/OS (going back almost 20
years) is a little mixed.
- JVM startup is rather expensive, especially the full JITing of classes.
- the more classes you pull in (like huge class libraries), the more
costs can get out of hand
- most Java programmers don't worry about what things cost (at all :-)
- long running apps that are well written and focus on performance can
run very well, even when compared to traditional MVS compiled languages
or even assembler - Not based on low level language metrics, but by
exploiting algorithms and class libraries for data structures, caching,
etc.
- good low-overhead (sampling) profiling tools for the z/OS JVM don't
exist (maybe this has changed?). IMO this was a huge barrier for Java
on z/OS.
- Sometimes CPU costs don't matter where time to market or functionality
are more important or where the application doesn't run that much.
Kirk Wolf
Dovetailed Technologies
http://dovetail.com
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