GC log is rotated too often on Java >= 9

[hmhagberg]

Issue Type:

• Bug report
• Feature request

What happened:

On Java >= 9, GC log is rotated when the log file reaches 10KB. Since only 10 files are kept around, linkerd starts to overwrite old GC logs very quickly. In our case, we have GC logs only for the last ~10 minutes.

What you expected to happen:

GC log rotation should be less aggressive.

On Java >= 9, which uses unified JVM logging, linkerd uses -Xlog option filesize=10000. The unit for filesize is bytes so log is rotated every 10KB. For Java 8, there is corresponding option -XX:GCLogFileSize=10M i.e. GC log is rotated when it reaches 10MB. I propose setting filesize=10M to match Java 8 behavior.

How to reproduce it (as minimally and precisely as possible):

Run linkerd with default GC log configuration. Observe that GC logs get rotated every 10KB.

Anything else we need to know?:

Environment:
linkerd 1.7.3 with Java11 but this affects older linkerd versions as well.