What's the impact of insufficient space for shared memory file in Java HotSpot?

Question

I have run a lot of experiments (months of cpu time) where I have the following warning in my log:

Java HotSpot(TM) 64-Bit Server VM warning: Insufficient space for shared memory file

The experiments terminated without error, but now I wonder what I may and may not evaluate from them. So:

What's the impact of insufficient space for shared memory file in Java HotSpot?

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Details:

All I have found about the shared memory file was http://openjdk.java.net/groups/hotspot/docs/Serviceability.html. From this, it does seem that the lack of the shared memory file has little effect on my experiments :) I do not use a profiler or the like for evaluating my experiments, but only the log file I have created successfully.

I measure how often function foo() is called. Can the lack of the shared memory file change the functional behaviour of my program, so that I should not evaluate this from the experiments?

Furthermore, I measure the runtime and memory requirements. Did the JVM's performance change, so that I should not evaluate this from the experiments?

Finally, I have experiments where I run a distributed version of my algorithm. Does JVM's performance change strongly, so that the parallel functional behaviour changes if the shared memory file is missing for some but not all of my parallel instances?

Answer 1

This warning means that JVM was unable to use memory-mapped file hsperfdata for HotSpot Performance Counters. In this case JVM falls back to standard (non-shared) memory for performance counters as if -XX:+PerfDisableSharedMem is specified.

This will prevent JVM from being automatically discovered by the utilities like jps, JConsole or VisualVM. jstat won't work. The application is not affected otherwise. The runtime performance is not changed.