Zing Startup Performance poor compared to Zulu


When migrating from Zulu JVM to Zing, the startup performance went from ~7 minutes to ~45 minutes.  This was a simple Zing JVM running TomCat in a Docker instance (12GB RAM, 6 Cores, 8GB heap).

Startup performance can be debugged by capturing the GC log and using the GC Log Analyzer tool ($JAVA_HOME/etc/GCLogAnalyzer2.jar) to analyze it.

However, in this case there was not very much activity in the GC log and nothing to explain the long startup time.  Compiler activity was relatively quiet.



Customer had previously used the following 3 "excludec2" directives with Zulu:


but was using the Falcon Compiler with Zing.  Falcon currently ignores "excludec2".

The following combination was determined to be the cause:

  • since "excludec2" was ignored, Falcon compiler had a huge memory requirement
  • -Xms2GB.  Zulu uses the -Xms parameter to start with a smaller heap, where Zing ignores it and immediately grows heap to (maximum) -Xmx, thereby causing a lot of disk swapping to occur (which didn't occur in Zulu)
  • Customer's heap was too large to work efficiently with a 12GB docker instance.  A larger instance or smaller heap should help improve performance



Replace the previouse "excludec2" directives with "excludefalcon".  For example:


This will reduce the load on the Falcon compiler to match what was observed in Zulu.



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