"... With Java and shared classes, it keeps a copy of the compiled
classes in a data space. "
Hmm ... Sounds (functionally) like LLA/VLF.
On 2021-10-22 05:21, Colin Paice wrote:
With Java and shared classes, it keeps a copy of the compiled classes in a
data space. You can now "save" the latest image to disk, and reload that
next time you run. If you save it every day, you will be able to restore
the latest and greatest optimised version.
Without the shared classes, the first use after IPL is slow, the second is
much faster. See "Some of the mysteries of Java shared classes"
<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcolinpaice.blog%2F2021%2F05%2F24%2Fsome-of-the-mysteries-of-java-shared-classes%2F&data=04%7C01%7C%7C51fe13f38fde46feae6b08d9953d67de%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637704913299328393%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=64i2zFrbqIdMwZ%2BokN3va%2B3NjZTpinrfu8tXWZ74rHY%3D&reserved=0>
On Fri, 22 Oct 2021 at 08:52, Andrew Rowley <[email protected]>
wrote:
On 22/10/2021 2:46 am, A T & T Management wrote:
Java, it has to be translated each time it run, provided you know
the language and it's been debugged. Schools may teach it but they too
want to make money and look good because they can say it's modern and that
is what they push. Any CEO or executive who doesn't look at the total cost
is doomed to fail.
Don't write off Java too quickly. I previously posted about Software
Drag Racing, which was a competition to test the speed of different
languages.
In the initial test on z/OS, Java was over 3 1/2 times faster than C++.
With some tweaking, C++ ran as fast as Java, but not significantly faster.
The results are written up here:
https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.blackhillsoftware.com%2Fnews%2F2021%2F08%2F10%2Fjava-vs-c-drag-racing-on-z-os%2F&data=04%7C01%7C%7C51fe13f38fde46feae6b08d9953d67de%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637704913299328393%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=P8SGNWwrhdsY4zjIL9a0PTOhnihTknXaYivvWbEaA7M%3D&reserved=0
If you have a zIIP and your general purpose CPs are not full speed, Java
might be the fastest language on your system by a big margin... and it
doesn't count against general purpose CP usage.
Java will compile to machine code where it makes a difference to
performance. Just in Time compilation has some performance advantages:
- it can optimize for the exact hardware
- it can leave out infrequently used code paths and compile them later
if they are actually required, making the machine code smaller and more
efficient
- it can monitor the code execution and recompile the hottest parts with
extra optimizations
IBM also talks a lot about RNI and processor cache... it turns out
garbage collection is good for cache efficiency too. It moves all the
active data into a smaller chunk of memory, which makes better use of
processor cache and is good for your RNI.
If you have well defined, well understood programs that are big CPU
users, it certainly could be worth rewriting them in Java.
(Knowing the language and debugging programs applies to any language...
and I'm not denying you can write large programs and inefficient code in
Java as much as in any other language.)
Andrew Rowley
Black Hill Software
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