[WEB][42108] Optimized JVM: Tune your Garbage collector

[JulienBertrand]

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Optimized JVM: Tune your Garbage collector

Platform

OS	OS version	Langage
-	-	Java

Main caracteristics

ID	Title	Category	Sub-category
CRJVM006-42108	Optimized JVM: Tune your Garbage collector	Environment	Optimized JVM

Severity / Remediation Cost

Severity	Remediation Cost
Minor	Minor

Rule short description

Using -XX:+UseG1GC and -XX:+UseStringDeduplication flags to tune your JVM to be more energy efficient.

Rule complete description

Text

Using -XX:+UseG1GC and -XX:+UseStringDeduplication flags to tune your JVM to be more energy efficient.

The -XX:+UseG1GC argument will change the garbage collector behaviorto be more energy efficient. Note that the G1GC is available since Java 8 and is the default value since Java 11.

The -XX:+UseStringDeduplication argument will attempts to eliminate duplicate strings as a part of the collection process

Code samples:

<!-- JIB Configuration -->
<jvmFlag>-XX:+UseG1GC</jvmFlag>
<jvmFlag>-XX:+UseStringDeduplication</jvmFlag>

#Docker file 
ENTRYPOINT exec java -XX:+UseG1GC -XX:+UseStringDeduplication -jar ./ecoCode.jar

Documentation:

• https://docs.oracle.com/javase/9/gctuning/garbage-first-garbage-collector.htm#JSGCT-GUID-98E80C82-24D8-41D4-BC39-B2583F04F1FF
• http://www.diva-portal.org/smash/get/diva2:1466940/FULLTEXT01.pdf

HTML

<p>Using <code>-XX:+UseG1GC</code> and <code>-XX:+UseStringDeduplication</code> flags to tune your JVM to be more energy efficient.</p>

<p>The <code>-XX:+UseG1GC</code> argument will change the garbage collector behavior to be more energy efficient.
</p>

<p>The <code>-XX:+UseStringDeduplication</code> argument will attempts to eliminate duplicate strings as a part of the collection process.
</p>

<h2>Compliant Solutions: </h2>
<pre>
    <!-- JIB Configuration -->
    <jvmFlag>-XX:+UseG1GC</jvmFlag>
    <jvmFlag>-XX:+UseStringDeduplication</jvmFlag>
</pre>
<pre>
    #Docker file 
    ENTRYPOINT exec java -XX:+UseG1GC -XX:+UseStringDeduplication -jar ./ecoCode.jar
</pre>

Implementation principle

• Inspect the deployement files (xml for JIB, Dockerfile, etc.)
• Inspect the running command line
• If the option does not include the params -XX:+UseG1GC (if 8 < java < 11) and -XX:+UseStringDeduplication add a code smell

[jhertout]

Hello,

For the use of G1GC:

• The issue targets the Java project configuration itself (via config files or command lines). We do not work on this for the moment but we will imagine that it is the case for the other points
• As far as I understand, the G1GC garbage collector seems to be more optimized than the CMS but we cannot affirm that using G1GC is better than CMS in term of energy. I think it is very dependent of the other options too. The provided documentation is not enough for me to justify G1GC is better
• Even if G1GC is better, detecting the use of G1GC is not a bad practice but a good practice. We do not work with "good practice" at the moment but maybe we can detect the use of another garbage collector as a bad practice? Moreover, since it is the default GC since Java 11, detecting the use of an other as a bad practice should be better.

I think the usage of the GC is a good thing to look at but at this point we cannot affirm which one is the best. And without looking at the options it is worse. For me, we cannot implement a rule at this point.

For use of UseStringDeduplication

To understand what the option does: https://dzone.com/articles/usestringdeduplication It seems to be a good idea to look at the option, even if its use is not quite simple and the improvement not always easy to see. However it is a "good practice" and we do not detect that in ecoCode and I am not sure we can throw a bad practice systematically if we do not found this option in the GC options wherever they are.

For the last reason, I think we cannot implement this rule in ecoCode.