CODEWITHSUNDEEP
javagarbage-collectionjvm
user2900180
user2900180

Reputation:

how to avoid GC pauses?

Our application is latency critical. In order to reduce GC pauses, we reuse objects. In beginning of the process we allocate a lot of small objects and then (almost) no memory allocated. However, I still see following log of gc: 

2016-12-18T13:51:48.650+0200: 1.085: Total time for which application threads were stopped: 0.0001411 seconds, Stopping threads took: 0.0000203 seconds
2016-12-18T13:51:48.776+0200: 1.210: Total time for which application threads were stopped: 0.0002027 seconds, Stopping threads took: 0.0000183 seconds
2016-12-18T13:51:48.894+0200: 1.328: Total time for which application threads were stopped: 0.0002559 seconds, Stopping threads took: 0.0000194 seconds
2016-12-18T13:51:48.906+0200: 1.341: Total time for which application threads were stopped: 0.0002159 seconds, Stopping threads took: 0.0000199 seconds
2016-12-18T13:51:49.047+0200: 1.482: Total time for which application threads were stopped: 0.0002842 seconds, Stopping threads took: 0.0000208 seconds

As far, as I understood, JVM stops process to run over all references and mark objects. Is it correct?

Also I see that frequency of such logs decrease with a time. So i think GC tunes some internal parameters and I wish to provide them on the start. Now I run process with following arguments:

-Xms10240m
-Xmx10240m
-server
-XX:+UseG1GC
-noclassgc

All rest arguments related to verbosing GC. Our machine have enough memory to completely avoid gc. How can I explain it to java?

OS: Linux, JVM either oracle or openJDK.

Thank you.

Upvotes: 2

Views: 1855

Answers (1)

apangin
apangin

Reputation: 98334

These are not necessarily garbage collections.

There is a number of other cases (not related to GC) when JVM prints Total time for which application threads were stopped. See the related answer for details.

Non-GC safepoints are especially frequent at application start-up time due to class loading and recompilation.

If you want to track GC pauses, use -XX:+PrintGCDetails.

Update

A few tricks to decrease number of non-GC safepoints:

  • -XX:-UseBiasedLocking completely disables bias revocation pauses;
  • -XX:+UnlockDiagnosticVMOptions -XX:GuaranteedSafepointInterval=0 disables an obligatory safepoint every second;
  • -XX:-TieredCompilation disables multi-tier compilation thus reducing number of recompilation-related safepoints.

Note: this is just a hint, not a suggestion for production use. The above options may have performance side effects.

Upvotes: 3

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