Tuning ShenandoahGC with 420 GB heaps

[Jeroen Borgers]

Hi,

First, thanks for the great work on ShenandoahGC! We want to use it for our
big heaps.
We have an application running with 420 GB heaps on a 24 core CPU (48
hardware threads) using ShenandoahGC. We have better results than G1, still
not as good as expected.
We have many degenerate GC pauses and some full GC pauses, last ones
typically of around 30 s. Requirements are pauses < 16 ms, so we are not
there yet. Load on the application is varying, with high load we get full
GC's.

We followed recommendations from the wiki. We enlarged heap size compared
to G1 (340 to 420 GB), ConcGCThreads (16 seems ok), ParallelGCThreads (44
seems ok), played with pacing delay (50 seems ok), spike factor (5 seems
ok) and we tried compact heuristics besides default adaptive. However, we
still get those degenerate and full gc pauses with durations far above our
requirements.

Would it make sense to post the complete configuration, statistics logged
and full gc log file? To get some tips, recommendations? The gc log file is
rather large.

Thanks in advance,

Kind regards,

Jeroen Borgers