Shenandoah Events

[Aleksey Shipilev]

On 1/23/19 5:04 PM, Ken Dobson wrote:
> Do you know of a good way to test the performance overhead of these events when they are enabled?

Apart from measuring the actual benchmarks, I don't know.

> As well, the goal with these events is to create something similar to the G1 Heap Layout in JMC
> (screenshot: https://gyazo.com/224574751d48804814163c280764bde5). It is used by selecting a GC event
> in the table on the right which will play the recorded heap information beginning at that GC,
> displaying the Heap Region state changes in a very similar manner to the Shenandoah Visualizer. Do
> you have any recommendations for changes or additional features you think would make it more useful
> for Shenandoah?

What Shenandoah Visualizer does would be good to have in JFR. Per-region history data would be nice
to have, as long as overhead is low.

Come to think about, I think intercepting the individual region transitions is too fine-grained for
this to have small theoretical overhead, because region states can change a lot. Do we have any idea
of the JFR sampling overhead both when enabled and disabled? That should indeed be our first question.

Our current scheme is snapshotting the heap state at low frequency (see ShenandoahRegionSampling),
the overhead for which should be low, and it can also be managed by controlling the frequency.

-Aleksey