Although the "Garbage-First garbage collector" would be quite useful for
Clojure, here I confirming that the new "G1" garbabe collector is "still in
beta" at least for a "comparative use case" (using velocity/groovy/jPython
in Xwiki, but not Clojure). Is anybody having success with theis GC in
Clojure in a more standalone environment?

> The Garbage-First garbage collector (G1) is currently in beta. It is
not enabled by default. The parallel collector is still the default GC and
is the most efficient GC for common household usage. G1 is meant to be
an alternative for the concurrent collector. It is designed to be
more predictable and enable fast allocation with memory regions design. To
use it: -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC
> For more information about GC & G1, please see:
>    - G1 Technical Session in JavaOne 2008<
http://developers.sun.com/learning/javaoneonline/j1sessn.jsp?sessn=TS-5419&yr=2008&track=javase
>
>    - Java SE 6 GC tunning<
http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html>
>    - Analysis of the Garbage-First Garbage Collection<
http://research.sun.com/jtech/pubs/04-g1-paper-ismm.pdf>

In my tests with Xwiki (which loads velocity, groovy, and jPython, but not
yet clojure) and Roller running out of Tomcat6, you unfortunately get a
Segmentation Fault at the end of the garbage collection (a regression, the
"early access release" ran successfully for 50 minutes under active
5-way-vhosting webload in Tomcat5):

# A fatal error has been detected by the Java Runtime Environment:

# SIGSEGV (0xb) at pc=0x00007f15ca60653a, pid=23777, tid=139729915439440

# JRE version: 6.0_14-b08

# Java VM: Java HotSpot(TM) 64-Bit Server VM (14.0-b16 mixed mode
> linux-amd64 )

# Problematic frame:

# V [libjvm.so+0x19c53a]


Caused by adding "-XX:+UnlockExperimentalVMOptions -XX:+UseG1GC" flags to
tomcat process below

F S UID        PID  PPID  C PRI  NI ADDR SZ WCHAN    RSS PSR STIME TTY
>  TIME CMD

0 S tomcat    8804     1  0  80   0 - 462172 futex_ 469116 1 Aug13 ?
>  9:04 /usr/java/default/bin/java -server -Xms160m -Xmx1024m
> -XX:PermSize=160m -XX:MaxPermSize=320m -XX:+DoEscapeAnalysis
> -XX:+UseBiasedLocking -XX:+AggressiveOpts 
> -Djavax.servlet.request.encoding=UTF-8
> -Dfile.encoding=UTF-8 -DjavaEncoding=UTF-8 -Djava.awt.headless=true
> -Djava.library.path=/usr/lib64 -classpath :/usr/share/tomcat6/bin/
> bootstrap.jar:/usr/share/tomcat6/bin/tomcat-juli.jar:/
> usr/share/java/commons-daemon.jar -Dcatalina.base=/usr/share/tomcat6
> -Dcatalina.home=/usr/share/tomcat6 -Djava.endorsed.dirs=
> -Djava.io.tmpdir=/var/cache/tomcat6/temp -Djava.util.logging.config.
> file=/usr/share/tomcat6/conf/logging.properties
> -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
> org.apache.catalina.startup.Bootstrap start.

Using: XWiki 2.0M2, Sun's jdk-1.6.0_14-fcs.x86_64,
> Fedora's tomcat6-6.0.18-6.2.fc10.noarch, tomcat-native-1.1.16-1.fc10.x86_64, 
> tomcat6-lib-6.0.18-6.2.fc10.noarch, 
> tomcat6-servlet-2.5-api-6.0.18-6.2.fc10.noarch, on
> "Linux 2.6.27.29-170.2.78.fc10.x86_64 #1 SMP Fri Jul 31 04:16:20 EDT 2009
> x86_64 x86_64 x86_64 GNU/Linux"

via $500 AMD Opteron 1220 2.80GHz Dual Core "server"
http://www.<http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4312771&CatId=1991>
> tigerdirect.com/applications/<http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4312771&CatId=1991>
> SearchTools/item-details.asp?<http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4312771&CatId=1991>
> EdpNo=4312771&CatId=1991<http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4312771&CatId=1991>


-- Niels
http://nielsmayer.com

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