compiler monitorig/tuning

Vladimir Kozlov vladimir.kozlov at
Wed Jun 22 04:01:31 UTC 2016

Hi Brian

Could you explain what problems you are observing? Which JDK 8 update version you are testing?

On 6/16/16 11:00 AM, Brian Toal wrote:
> Good day,
> - How do I monitor the length of the compiler queues (client and server)?  I want to understand the backlog (if any) to
> determine if the application could benefit from more compilation threads.

There is -XX:+PrintTieredEvents flag which outputs on display queues sizes for each compilation request (a lot of output).

> - I remember in the past being able to get detailed compiler statistics from a mbean or something where the metric was
> prefixed with <> and it contained execution count, total time, thread count exec for the client
> and server compilers.  Where can I find this data in realtime for monitoring purposes?  If I know the total time and
> thread count I suppose I can work out if the utilization of the compilation threads.

May be it was jvmstat monitoring utility (now jstat). But it does not collect queues sizes.

> - What other compilation metrics should I be paying close attention to?

Very detailed compilation output file is created (on JVM exit) with -XX:+UnlockDiagnosticVMOptions -XX:+LogCompilation.
You can build this output parser tool from sources in (note it is jdk 9, for 
8 update build from clone of

> - Other than tiered compilation becoming the default in Java 8, where there any significant changes that would have
> slowed down compilation time?  We've had -XX:-TieredCompilation set in Java 7 and 8 and haven't touched any other JIT
> related config.  Was there some other setting default that changed which we would have needed to change when going fro 7
> to 8?  Looking at the various compiler parameters that I know about via PrintFlagsFinal from 7 and 8, there doesn't seem
> to be any change other than -XX:-TieredCompilation.

There were a lot of changes which could affected JIT compilation speed.

> Regards,
> - Brian


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