cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Durity, Sean R" <>
Subject RE: [EXTERNAL] Re: GC Tuning
Date Mon, 21 Oct 2019 15:38:46 GMT
I don’t disagree with Jon, who has all kinds of performance tuning experience. But for ease
of operation, we only use G1GC (on Java 8), because the tuning of ParNew+CMS requires a high
degree of knowledge and very repeatable testing harnesses. It isn’t worth our time. As a
previous writer mentioned, there is usually better return on our time tuning the schema (aka
helping developers understand Cassandra’s strengths).

We use 16 – 32 GB heaps, nothing smaller than that.

Sean Durity

From: Jon Haddad <>
Sent: Monday, October 21, 2019 10:43 AM
Subject: [EXTERNAL] Re: GC Tuning

I still use ParNew + CMS over G1GC with Java 8.  I haven't done a comparison with JDK 11 yet,
so I'm not sure if it's any better.  I've heard it is, but I like to verify first.  The pause
times with ParNew + CMS are generally lower than G1 when tuned right, but as Chris said it
can be tricky.  If you aren't willing to spend the time understanding how it works and why
each setting matters, G1 is a better option.

I wouldn't run Cassandra in production on less than 8GB of heap - I consider it the absolute
minimum.  For G1 I'd use 16GB, and never 4GB with Cassandra unless you're rarely querying

I typically use the following as a starting point now:

ParNew + CMS
16GB heap
10GB new gen
2GB memtable cap, otherwise you'll spend a bunch of time copying around memtables (cassandra.yaml)
Max tenuring threshold: 2
survivor ratio 6

I've also done some tests with a 30GB heap, 24 GB of which was new gen.  This worked surprisingly
well in my tests since it essentially keeps everything out of the old gen.  New gen allocations
are just a pointer bump and are pretty fast, so in my (limited) tests of this I was seeing
really good p99 times.  I was seeing a 200-400 ms pause roughly once a minute running a workload
that deliberately wasn't hitting a resource limit (testing real world looking stress vs overwhelming
the cluster).

We built tlp-cluster [1] and tlp-stress [2] to help figure these things out.

[1] []<;!OYIaWQQGbnA!ZhiXAdRaL49J8nBlh0F_5MQ97Z1QNTUuTSMvksmEmxan3d65D6ATmQO1ig58W52u_EmQ1GM$>
[2] []<;!OYIaWQQGbnA!ZhiXAdRaL49J8nBlh0F_5MQ97Z1QNTUuTSMvksmEmxan3d65D6ATmQO1ig58W52uuCUZYKw$>


On Mon, Oct 21, 2019 at 10:24 AM Reid Pinchback <<>>
An i3x large has 30.5 gb of RAM but you’re using less than 4gb for C*.  So minus room for
other uses of jvm memory and for kernel activity, that’s about 25 gb for file cache.  You’ll
have to see if you either want a bigger heap to allow for less frequent gc cycles, or you
could save money on the instance size.  C* generates a lot of medium-length lifetime objects
which can easily end up in old gen.  A larger heap will reduce the burn of more old-gen collections.
 There are no magic numbers to just give because it’ll depend on your usage patterns.

From: Sergio <<>>
Reply-To: "<>" <<>>
Date: Sunday, October 20, 2019 at 2:51 PM
To: "<>" <<>>
Subject: Re: GC Tuning []<;!OYIaWQQGbnA!ZhiXAdRaL49J8nBlh0F_5MQ97Z1QNTUuTSMvksmEmxan3d65D6ATmQO1ig58W52uwG_KUYM$>

Message from External Sender
Thanks for the answer.

This is the JVM version that I have right now.

openjdk version "1.8.0_161"
OpenJDK Runtime Environment (build 1.8.0_161-b14)
OpenJDK 64-Bit Server VM (build 25.161-b14, mixed mode)

These are the current flags. Would you change anything in a i3x.large aws node?

java -Xloggc:/var/log/cassandra/gc.log -Dcassandra.max_queued_native_transport_requests=4096
-ea -XX:+UseThreadPriorities -XX:ThreadPriorityPolicy=42 -XX:+HeapDumpOnOutOfMemoryError -Xss256k
-XX:StringTableSize=1000003 -XX:+AlwaysPreTouch -XX:-UseBiasedLocking -XX:+UseTLAB -XX:+ResizeTLAB
-XX:+UseNUMA -XX:+PerfDisableSharedMem -XX:SurvivorRatio=8
-XX:MaxTenuringThreshold=1 -XX:+UseG1GC -XX:G1RSetUpdatingPauseTimePercent=5 -XX:MaxGCPauseMillis=200
-XX:InitiatingHeapOccupancyPercent=45 -XX:G1HeapRegionSize=0 -XX:-ParallelRefProcEnabled -Xms3821M
-Xmx3821M -XX:CompileCommandFile=/etc/cassandra/conf/hotspot_compiler
-Djava.library.path=/usr/share/cassandra/lib/sigar-bin -Djava.rmi.server.hostname=
-XX:+CMSClassUnloadingEnabled -javaagent:/usr/share/cassandra/lib/jmx_prometheus_javaagent-0.3.1.jar=10100:/etc/cassandra/default.conf/jmx-export.yml
-Dlogback.configurationFile=logback.xml -Dcassandra.logdir=/var/log/cassandra -Dcassandra.storagedir=
-Dcassandra-pidfile=/var/run/cassandra/ -Dcassandra-foreground=yes -cp /etc/cassandra/conf:/usr/share/cassandra/lib/airline-0.6.jar:/usr/share/cassandra/lib/antlr-runtime-3.5.2.jar:/usr/share/cassandra/lib/asm-5.0.4.jar:/usr/share/cassandra/lib/caffeine-2.2.6.jar:/usr/share/cassandra/lib/cassandra-driver-core-3.0.1-shaded.jar:/usr/share/cassandra/lib/commons-cli-1.1.jar:/usr/share/cassandra/lib/commons-codec-1.9.jar:/usr/share/cassandra/lib/commons-lang3-3.1.jar:/usr/share/cassandra/lib/commons-math3-3.2.jar:/usr/share/cassandra/lib/compress-lzf-0.8.4.jar:/usr/share/cassandra/lib/concurrentlinkedhashmap-lru-1.4.jar:/usr/share/cassandra/lib/concurrent-trees-2.4.0.jar:/usr/share/cassandra/lib/disruptor-3.0.1.jar:/usr/share/cassandra/lib/ecj-4.4.2.jar:/usr/share/cassandra/lib/guava-18.0.jar:/usr/share/cassandra/lib/HdrHistogram-2.1.9.jar:/usr/share/cassandra/lib/high-scale-lib-1.0.6.jar:/usr/share/cassandra/lib/hppc-0.5.4.jar:/usr/share/cassandra/lib/jackson-core-asl-1.9.13.jar:/usr/share/cassandra/lib/jackson-mapper-asl-1.9.13.jar:/usr/share/cassandra/lib/jamm-0.3.0.jar:/usr/share/cassandra/lib/javax.inject.jar:/usr/share/cassandra/lib/jbcrypt-0.3m.jar:/usr/share/cassandra/lib/jcl-over-slf4j-1.7.7.jar:/usr/share/cassandra/lib/jctools-core-1.2.1.jar:/usr/share/cassandra/lib/jflex-1.6.0.jar:/usr/share/cassandra/lib/jmx_prometheus_javaagent-0.3.1.jar:/usr/share/cassandra/lib/jna-4.2.2.jar:/usr/share/cassandra/lib/joda-time-2.4.jar:/usr/share/cassandra/lib/json-simple-1.1.jar:/usr/share/cassandra/lib/jstackjunit-0.0.1.jar:/usr/share/cassandra/lib/libthrift-0.9.2.jar:/usr/share/cassandra/lib/log4j-over-slf4j-1.7.7.jar:/usr/share/cassandra/lib/logback-classic-1.1.3.jar:/usr/share/cassandra/lib/logback-core-1.1.3.jar:/usr/share/cassandra/lib/lz4-1.3.0.jar:/usr/share/cassandra/lib/metrics-core-3.1.5.jar:/usr/share/cassandra/lib/metrics-jvm-3.1.5.jar:/usr/share/cassandra/lib/metrics-logback-3.1.5.jar:/usr/share/cassandra/lib/netty-all-4.0.44.Final.jar:/usr/share/cassandra/lib/ohc-core-0.4.4.jar:/usr/share/cassandra/lib/ohc-core-j8-0.4.4.jar:/usr/share/cassandra/lib/reporter-config3-3.0.3.jar:/usr/share/cassandra/lib/reporter-config-base-3.0.3.jar:/usr/share/cassandra/lib/sigar-1.6.4.jar:/usr/share/cassandra/lib/slf4j-api-1.7.7.jar:/usr/share/cassandra/lib/snakeyaml-1.11.jar:/usr/share/cassandra/lib/snappy-java-



Il giorno sab 19 ott 2019 alle ore 14:30 Chris Lohfink <<>>
ha scritto:
"It depends" on your version and heap size but G1 is easier to get right so probably wanna
stick with that unless you are using small heaps or really interested in tuning it (likely
for massively smaller gains then tuning your data model). There is no GC algo that is strictly
better than others in all scenarios unfortunately. If your JVM supports it, ZGC or Shenandoah
are likely going to give you the best latencies.


On Fri, Oct 18, 2019 at 8:41 PM Sergio Bilello <<>>

Is it still better to use ParNew + CMS Is it still better than G1GC  these days?

Any recommendation for i3.xlarge nodes read-heavy workload?



To unsubscribe, e-mail:<>
For additional commands, e-mail:<>


The information in this Internet Email is confidential and may be legally privileged. It is
intended solely for the addressee. Access to this Email by anyone else is unauthorized. If
you are not the intended recipient, any disclosure, copying, distribution or any action taken
or omitted to be taken in reliance on it, is prohibited and may be unlawful. When addressed
to our clients any opinions or advice contained in this Email are subject to the terms and
conditions expressed in any applicable governing The Home Depot terms of business or client
engagement letter. The Home Depot disclaims all responsibility and liability for the accuracy
and content of this attachment and for any damages or losses arising from any inaccuracies,
errors, viruses, e.g., worms, trojan horses, etc., or other items of a destructive nature,
which may be contained in this attachment and shall not be liable for direct, indirect, consequential
or special damages in connection with this e-mail message or its attachment.
View raw message