-XX:+UseConcMarkSweepGC JAVA_OPTS slows down logstash by ~20%

[colinsurprenant]

per #2859 we realized that using the -XX:+UseConcMarkSweepGC JAVA_OPTS slows down logstash by about 20%.

[colinsurprenant]

I will put it as blocker for 1.5, we need to figure if using the CMS garbage collector is necessary and has benefits over using the default ParallelGC. Currently the default logstash JAVA_OPTS are:

LS_HEAP_SIZE="${LS_HEAP_SIZE:=500m}"

JAVA_OPTS="$JAVA_OPTS -Xmx${LS_HEAP_SIZE}"
JAVA_OPTS="$JAVA_OPTS -XX:+UseParNewGC"
JAVA_OPTS="$JAVA_OPTS -XX:+UseConcMarkSweepGC"
JAVA_OPTS="$JAVA_OPTS -Djava.awt.headless=true"

JAVA_OPTS="$JAVA_OPTS -XX:CMSInitiatingOccupancyFraction=75"
JAVA_OPTS="$JAVA_OPTS -XX:+UseCMSInitiatingOccupancyOnly"

[colinsurprenant]

I tried to search the git log for the rational for using these settings but did not find anything.

These settings are the same as in elasticsearch, maybe it was decided that these settings would also benefit logstash, and maybe in particular when using the embedded elasticsearch?

In any case, I do not believe we actually need to enable the CMS GC since the heap usage signature of logstash is not like with elasticsearch. ES experiences memory usage spikes and want to really minimize stop-the-world situations. Also, using embedded elasticsearch in logstash is not recommended for production and is only there for easier prototyping/testing so we should not set default GC options for that use-case.

logstash will typically have a rather stable heap usage pattern. given enough memory, I do not believe there is any benefit for using CMS GC at the cost of a ~20% overall performance drop. also, a stop-the-world situation in logstash is not critical as opposed to in elasticsearch. In fact, I think logstash would benefit from having a larger GC Young Generation heap space using either -XX:NewSize= or -XX:NewRatio= because logstash has typically a rather constant old generation heap.

thoughts?

I suggest we remove these JVM options by default and also make JAVA_OPTS overridable on the command line, for example:

JAVA_OPTS="-Xmx500m -XX:NewSize=400m" bin/logstash ...

Also, as in elasticsearch, I suggest we also set these option by default in logstash:

-Djava.net.preferIPv4Stack=true
-XX:+HeapDumpOnOutOfMemoryError

[colinsurprenant]

using simple pipeline performance configurations defined in #2870 I can see a ~10% performance increase between using only these JAVA_OPTS:

JAVA_OPTS="-Xmx500m"

vs

JAVA_OPTS="-Xmx500m -XX:NewSize=400m"

for these configs, using a larger youg generation heap performs better.

[untergeek]

This is really interesting. It's also very important to understand and document well because JVM settings could have a profound impact on those who are still trying to use the embedded Elasticsearch.

[purbon]

@colinsurprenant this makes complete sense to me to investigate prior to 1.5 GA, we have as @untergeek said understand better our specific GC needs, ...

Not sure if this qualify, but I see our GC needs as something that depends highly on our pipeline usage, right? I mean what might be the difference with doing lots of Groks or not? for example.

Definitely something important to dig into

[purbon]

We agree on having different options + having the option to overwrite this options from the client side point of view.

[jsvd]

Test:

bin/logstash -e 'input { generator { count => 10000000 } } output { stdout { codec => dots } }' | pv -War > /dev/null

JVM flags	Time
1.5.rc2 flags (CMS)	1:25.54 - 126kiB/s
No CMS flags	1:17.52 - 141kiB/s
No CMS flags + NewRatio=3	1:18.93 - 138kiB/s
No CMS flags + NewRatio=2	1:13.66 - 149kiB/s

So my proposal:

iff --git a/bin/logstash.lib.sh b/bin/logstash.lib.sh
index 1b1fc46..a6fe590 100755
--- a/bin/logstash.lib.sh
+++ b/bin/logstash.lib.sh
@@ -20,18 +20,15 @@ setup_java() {
   fi

   JAVA_OPTS="$JAVA_OPTS -Xmx${LS_HEAP_SIZE}"
-  JAVA_OPTS="$JAVA_OPTS -XX:+UseParNewGC"
-  JAVA_OPTS="$JAVA_OPTS -XX:+UseConcMarkSweepGC"
+  JAVA_OPTS="$JAVA_OPTS -XX:NewRatio=2"
   JAVA_OPTS="$JAVA_OPTS -Djava.awt.headless=true"

-  JAVA_OPTS="$JAVA_OPTS -XX:CMSInitiatingOccupancyFraction=75"
-  JAVA_OPTS="$JAVA_OPTS -XX:+UseCMSInitiatingOccupancyOnly"
-
   if [ ! -z "$LS_USE_GC_LOGGING" ] ; then
     JAVA_OPTS="$JAVA_OPTS -XX:+PrintGCDetails"
     JAVA_OPTS="$JAVA_OPTS -XX:+PrintGCTimeStamps"

[ph]

Could we do a check with real world data? Maybe using the HOW's complete.conf?

[purbon]

@ph I'm doing this right now

[purbon]

I'm using also different datasets that I've spare in here.

[ph]

❤️

[purbon]

Hi,
I did some micro benchmarking with the generated messages and this are my numbers, please let me know if you see something strange, because I don't see a lot of benefit (in this exact case) to change GC options.

Here is my report:

CONFIG="input { generator { count => 10000000 } } output { stdout { codec => dots } }"

	AVG (s)	Diff	EPS
1	51.01		196046.9101
2	49.55	2.86%	201809.8306
3	50.62	0.77%	197569.1097
4	47.66	6.57%	209834.5245
5	51.80	-1.54%	193068.0835

CONFIG="input { generator { count => 100000000 } } output { stdout { codec => dots } }"

	AVG (s)	Diff	EPS
1	460.71		217054.7751
2	452.90	1.69%	220796.9534
3	491.92	-6.77%	203285.5003
4	430.94	6.46%	232051.1886
5	496.06	-7.67%	201587.1358

Executions are made with this set of ENV variables

1. Default options.
2. ENV['LS_HEAP_SIZE']="500m"
3. ENV['LS_HEAP_SIZE']="500m" ENV['LS_JAVA_OPTS']="-XX:NewRatio=2"
4. ENV['LS_HEAP_SIZE']="500m" ENV['LS_JAVA_OPTS']="-XX:+UseParNewGC -XX:NewRatio=2"
5. ENV['LS_HEAP_SIZE']="500m" ENV['LS_JAVA_OPTS']="-XX:+UseParallelGC -XX:NewRatio=2"

purbon@Ubuntu-1404-trusty-64-minimal:~/_gc_config_benchmark/reports$ java -version
java version "1.7.0_65"
OpenJDK Runtime Environment (IcedTea 2.5.3) (7u71-2.5.3-0ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode)

purbon@Ubuntu-1404-trusty-64-minimal:~/_gc_config_benchmark/reports$ ruby -v
jruby 1.7.16.1 (1.9.3p392) 2014-10-28 4e93f31 on OpenJDK 64-Bit Server VM 1.7.0_65-b32 +jit [linux-amd64]

and using the vendored JRuby.

This is done using master and running it with as in

bin/logstash -e $CONFIG | pv ....

so as I said, using the vendored jruby.

thoughts why do I get this numbers?

[purbon]

Now I'm doing some micro benchmarking with more complex configuration and datasets, as in with a set of apache logs and a set of xml documents. Will report numbers in here soon.

[colinsurprenant]

can you share the exact command lines you used to do the benchmarks. also exactly which LS version you used? master?

[purbon]

Yes, sure, updating my comment so it stays all together.

[purbon]

Updating the numbers as requested by @colinsurprenant so the reported number is the one given back by pv, not the timing as it's now.

[jsvd]

test: bin/logstash -e 'input { generator { count => 10000000 } } output { stdout { codec => dots } }'

Vanilla JVM flags on master:

joaoduarte@Joaos-MacBook-Pro-2 ~/projects/logstash (git)-[master] % bin/logstash -e 'input { generator { count => 10000000 } } output { stdout { codec => dots } }'
--1.9 -J-Xmx500m -J-XX:+UseParNewGC -J-XX:+UseConcMarkSweepGC -J-Djava.awt.headless=true -J-XX:CMSInitiatingOccupancyFraction=75 -J-XX:+UseCMSInitiatingOccupancyOnly
[ 142kiB/s] [ 142kiB/s]
bin/logstash -e   153.73s user 55.72s system 272% cpu 1:16.82 total

Disabling CMS:

joaoduarte@Joaos-MacBook-Pro-2 ~/projects/logstash (git)-[master] % bin/logstash -e 'input { generator { count => 10000000 } } output { stdout { codec => dots } }'
--1.9 -J-Xmx500m -J-Djava.awt.headless=true
[ 151kiB/s] [ 151kiB/s]
bin/logstash -e   144.49s user 53.03s system 270% cpu 1:12.99 total

Disabling CMS + Increasing New Gen size:

joaoduarte@Joaos-MacBook-Pro-2 ~/projects/logstash (git)-[master] % bin/logstash -e 'input { generator { count => 10000000 } } output { stdout { codec => dots } }'
--1.9 -J-Xmx500m -J-XX:NewRatio=3 -J-Djava.awt.headless=true
[ 155kiB/s] [ 155kiB/s]
bin/logstash -e   143.83s user 51.67s system 272% cpu 1:11.72 total

Vanilla flags again after previews tests:

joaoduarte@Joaos-MacBook-Pro-2 ~/projects/logstash (git)-[master] % bin/logstash -e 'input { generator { count => 10000000 } } output { stdout { codec => dots } }'
--1.9 -J-Xmx500m -J-XX:+UseParNewGC -J-XX:+UseConcMarkSweepGC -J-Djava.awt.headless=true -J-XX:CMSInitiatingOccupancyFraction=75 -J-XX:+UseCMSInitiatingOccupancyOnly
[ 138kiB/s] [ 138kiB/s]
bin/logstash -e   154.14s user 54.31s system 262% cpu 1:19.29 total

So --1.9 -J-Xmx500m -J-XX:NewRatio=3 -J-Djava.awt.headless=true wins!

[colinsurprenant]

@jsvd note that a higher value of -XX:NewRatio results in a larger old generation size. The JVM default in server mode is 2 and the biggest young generation possible when using -XX:NewRatio is to set it to -XX:NewRatio=1.

Since the only significative difference we can measure is by removing the CMS I would go ahead and remove that from the defaults but keep the rest as is. In other words, I would remove these options:

JAVA_OPTS="$JAVA_OPTS -XX:+UseConcMarkSweepGC"
JAVA_OPTS="$JAVA_OPTS -XX:CMSInitiatingOccupancyFraction=75"
JAVA_OPTS="$JAVA_OPTS -XX:+UseCMSInitiatingOccupancyOnly"

[colinsurprenant]

relates to #2942

[colinsurprenant]

we decided to not put it as blocker for RC3, this will be pushed back to the next release (either 1.5.1 or 1.6.0). OTH we will merge #2942 so that we have a way to completely override JAVA_OPTS and thus remove any CMS if we wish to.

[felipegs]

If I use elasticsearch output, with protocol option as node, has impact on this?
Because if I do that it starts an elasticsearch inside same jvm process, but it only act as a client node of elasticsearch cluster

[colinsurprenant]

@felipegs no it should not. the CMS GC option will be useful when memory pressure increases and that typically happens on ES data nodes.

[ppf2]

+1 on adding heap dump on oom flag like Elasticsearch, eg.

# Causes the JVM to dump its heap on OutOfMemory.
JAVA_OPTS="$JAVA_OPTS -XX:+HeapDumpOnOutOfMemoryError"
# The path to the heap dump location, note directory must exists and have enough
# space for a full heap dump.
#JAVA_OPTS="$JAVA_OPTS -XX:HeapDumpPath=$ES_HOME/logs/heapdump.hprof"

[splitice]

By setting -Xmx450m -XX:NewSize=375m (same ratio as @colinsurprenant) we saw an increase of 15-20% on a single core 512mb ram logstash worker. Tested on 4 such nodes, all with the same results.

This is under realworld conditions and a pretty large & complex production configuration.

[jordansissel]

I tried to search the git log for the rational for using these settings but did not find anything.

If I recall correctly, I made this change because it was already what Elasticsearch was using.

[colinsurprenant]

bump. we should reassess this WRT ng-pipeline and logstash-core-event-java but I believe there are no benefit for using CMS - the Elasticsearch heap usage pattern is nowhere similar to logstash and so far all tests seems to indicate a non-negligible performance increase.

[untergeek]

+1

[geoffroya]

Hi all

I have just remove CMS and leaving default GC behaviour and -XX:NewSize, and logstash stopped garbage collecting like a fool.

I can't imagine LS v5 release without GC that can be (easily) settable, or at least documented.

For those interested in changing GC just through config, use /etc/default/logstash:

...
# Arguments to pass to java
LS_HEAP_SIZE="400m"
#LS_JAVA_OPTS="-Djava.io.tmpdir=$HOME"

JAVA_OPTS="-Djava.awt.headless=true"
JAVA_OPTS="$JAVA_OPTS -XX:NewSize=200m"
export JAVA_OPTS
# Need this because /opt/logstash/bin/logstash.lib.sh ruby_exec() waits for this var => should be configurable IMHO
export HEAP_DUMP_PATH="-XX:HeapDumpPath=/tmp/heapdump.hprof"
...

[jordansissel]

Based onthe evidence so far, I am +1 on changing the default GC parameters for Logstash 5.0.0 do whatever we find is best.

[marek-obuchowicz]

+1... CMS is supposed to offer possibly short stop-the-world phases, which are important for real-time or event-based applications (ie. get response to ES request as soon as possible). Logstash is about throughput and having longer single GC pauses with smaller total GC overhead is definitely welcome. Possibly even earlier as 5.0 - it's a small change in init scripts, does not depend on new code and could be published soon

[andrewvc]

I realize its late, but just to add something here, we haven't supported embedded ES for quite some time now. We pulled it out somewhere in 2.x

[untergeek]

The changes in #5341 should make it easy to both change this default, and also for users to change it to something they like.

[jsvd]

Have we run tests where a full GC is actually triggered during ingestion? It seems very reasonable that CMS is slower because it avoids full GCs, but I'd like to see how long that takes on a busy logstash instance, with the added caveat that such stops mean packet loss for plugins like UDP input.

[marek-obuchowicz]

Inputs without ack mechanism (like udp) will be surely negatively affected.

[deepakm14]

any suggest how do i fix issue

[GC (Metadata GC Threshold) 8530310K->2065630K(31574016K), 0.3831399 secs]
[Full GC (Metadata GC Threshold) 2065630K->2053217K(31574016K), 3.5927870 secs]
[GC (Metadata GC Threshold) 8061486K->2076192K(31574016K), 0.0096316 secs]
[Full GC (Metadata GC Threshold) 2076192K->2055722K(31574016K), 0.9376524 secs]
[GC (Metadata GC Threshold) 8765230K->2100440K(31574016K), 0.0150190 secs]
[Full GC (Metadata GC Threshold) 2100440K->2077052K(31574016K), 4.1662779 secs]

[remtcsdev]

Seems UseConcMarkSweepGC is to be removed shortly, and currently produces this warning on Logstash startup on Java 11.

OpenJDK 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release.