Generally you try to prestart the JVM, so you get the startup time out of the way. That may or may not be possible here.

I know that IBM used to recommend the 32-bit JVM unless you specifically needed the 64-bit version. I don't recall if that was for performance or other reasons.

What's making the connection that seems to be timing out? If the connection comes from the Java app running on IBMi, I'd expect you to be past the JVM startup.




-----Original Message-----
From: Duncan McManus [mailto:Duncan.McManus@xxxxxxxxxxx]
Sent: Monday, March 18, 2019 11:37 AM
To: 'java400-l@xxxxxxxxxxxxxxxxxx' <java400-l@xxxxxxxxxxxxxxxxxx>
Subject: Java startup performance

Hi All

How can I improve the startup performance of Java applications on the AS/400?

We have an application that connects to an external system. However, this takes so long to start up on the AS/400, that it always fails to connect first time.

The communication is performed by an open source tool (Quickfix/J) which uses Apache Mina to perform the underlying socket communications. The socket is opened, but it then takes 10-15 seconds to send the first message. The external server seems to close the socket if nothing happens within 5 seconds - hence the initial failure. Thereafter it is much quicker.

I believe this is to do with the class loading and JIT that is making the first attempt so slow.

If I run the exact same java application on a PC, then this occurs in approximately 1 second. I have tested this by placing a TCP trace tool in between the java application and the server. If I add in a manual delay on the PC (just for testing) then I can see it receiving the same reject.

The startup performance occurs on all our java applications (not just with this tool). However, it is particularly causing a problem with this one.

Any help appreciated.

I believe the system is a power 8 server (relatively new and otherwise fairly quick). OS level is on V7R1. Java used is JDK 8 (64-bit).

Thanks
Duncan



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