Are there also some conferences where OpenJ9 devs take part
usually? Preferably in Europe.
Default increment is 3ms in Metronome, but you
can override it to be 1ms - it should be obeyed most of the
time.
Note also, there is concept of a utilisation
sliding window, which controls how many of those increments
you can have within a window of time (https://www.ibm.com/developerworks/library/j-rtj4/index.html)
The more demanding you are on individual pause
times and utilisation, the more you have to compromise
throughput and/or heap size.
akrus ---11/20/2017 02:03:59
PM---Lowest possible latency is the priority (HFT), <1ms,
worst case 10ms. From: Aleksandar Micic <Aleks
From: akrus
<akrus@xxxxxxxxxxx>
To: openj9
developer discussions <openj9-dev@xxxxxxxxxxx>
Date: 11/20/2017
02:03 PM
Subject: Re:
[openj9-dev] OpenJ9 question
Sent by: openj9-dev-bounces@xxxxxxxxxxx
Lowest possible latency is
the priority (HFT), <1ms, worst case 10ms.
From:
Aleksandar Micic <Aleksandar_Micic@xxxxxxxxxx>
Sent: 20 Nov 2017 8:58 pm
To: openj9 developer
discussions
Subject: Re: [openj9-dev]
OpenJ9 question
I do not have comparison data against Azul Zing.
Btw, what are you requirements or concerns: latency (worst
case, average, distribution) or throughput?
Metronome does have excellent pause time control, but it will
compromise some throughput (against default Gencon GC policy)
due to 1) not being generational and 2) various techniques to
reduce fragmentation to avoid compaction.
A.
akrus ---11/20/2017 01:35:43
PM---Hi Aleksandar, Thanks a lot for the information!
From: akrus <akrus@xxxxxxxxxxx>
To: openj9 developer discussions
<openj9-dev@xxxxxxxxxxx>
Date: 11/20/2017 01:35 PM
Subject: Re: [openj9-dev] OpenJ9
question
Sent by: openj9-dev-bounces@xxxxxxxxxxx
Hi Aleksandar,
Thanks a lot for the information!
Also one small question I wanted to ask - since IBM J9 was a
commercial product, how does it compare to Azul Zing? Since Zing
is mostly used on low latency apps, wondering if OpenJ9 would be
a better choice considering the open source model.
From: Aleksandar Micic
<Aleksandar_Micic@xxxxxxxxxx>
Sent: 20 Nov 2017 8:21 pm
To: openj9-dev@xxxxxxxxxxx
Subject: Re: [openj9-dev]
OpenJ9 question
Hi Akrus, here are responses to a few questions:
2) with -Xgcpolicy:metronome and heap >25Gb I get this
message:
Selected VM [default] does not exist.
Metronome does support heaps larger than 25g however it does
not support 4-bit shift Compressed Refs for heaps 32g-64g. The
observed behavior is a problem in redirector. The work around
would be run with -Xnocompressedrefs or run with
-Xcompressedrefs but with limitation of virtual memory below
32g
3) what's the best GC option for low latency apps? Does do not
say this directly, but is it Metronome? Are there any flags than
can further reduce GC pauses? -Xrealtime doesn't work, is it
unavailable completely or it's a part of some subscription?
Yes, Metronome GC policy is best for low latency. Tuning
options are here: https://www.ibm.com/support/knowledgecenter/en/SSYKE2_8.0.0/com.ibm.java.lnx.80.doc/user/mgc/metronome.html
We also have the very new low-pause variant on Gencon GC
policy with Concurrent Scavenger, but it's only available on
newest IBM's Z series machines.
5) how to rotate GC logs?
Rolling verbose GC logs: https://www.ibm.com/support/knowledgecenter/en/SSYKE2_8.0.0/com.ibm.java.lnx.80.doc/diag/appendixes/cmdline/xverbosegclog.html Not sure what is meant by flush on signal. Our logs
are by default synchronous, so there is no need for an
explicit flush for ongoing logging - they are written in a
file as soon as they are generated. If, however, by this is
meant: close the current file and start using a new file, I
don't think we support it.
Regards,
Aleks
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