Big speed difference for G1 vs. parallel GC

[Peter]

Hi,

I've stumbled today* over a big speed difference for code execution with
G1 GC vs. parallel GC also in the latest JDK8 (1.8.0_111-b14). Maybe you
have interests to investigate this. You should be able to reproduce this
via:

# setup
git clone https://github.com/graphhopper/graphhopper
wget http://download.geofabrik.de/europe/germany/bayern-latest.osm.pbf
cd graphhopper

# run measurement
export JAVA_OPTS="-XX:+UseParallelGC -Xmx1000m -Xms1000m"
# the graphhopper.sh script just makes the installation of maven and
bundling the jar a bit simpler
# you can also execute the tests in the class Measurement.java
<https://github.com/graphhopper/graphhopper/blob/master/tools/src/main/java/com/graphhopper/tools/Measurement.java>
./graphhopper.sh clean
./graphhopper.sh measurement berlin-latest.osm.pbf
# now a measurement-<some date>.properties is created:
grep routing.mean measurement-XY.properties

Now this should print a line where the value is in ms. E.g. I get ~450ms
for the parallel GC and ~780ms for G1GC (on an old laptop). When I
increase the Xmx for the G1 run to 1400m the results do NOT get closer
to parallel GC!

Let me know if you need more information!

Regards
Peter

*
https://github.com/graphhopper/graphhopper/issues/854

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