Darrel Schneider created GEODE-2035:
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Summary: document how to use G1GC with geode
Key: GEODE-2035
URL: https://issues.apache.org/jira/browse/GEODE-2035
Project: Geode
Issue Type: Task
Components: docs
Reporter: Darrel Schneider
The geode docs should describe how to configure G1GC for geode.
One issue is that if you use "gfsh start server --max-heap=SIZE" then it will
automatically configure CMS which does not work with G1GC.
So instead of using the --max-heap we should tell them to use "--J-XmxSIZE".
To configure G1GC use "--J-XX:+UseG1GC".
If you find the geode resource manager does not detect crossing the eviction or
critical threshold quickly enough then try using this option to make it more
responsive: "--J-XX:MaxGCPauseMillis=VALUE" where VALUE should be a number less
than 200 (which is the current G1GC default). We have done some limited testing
with this value set to 1 and it does make the resource manager more responsive
when combined with G1GC but it also increases the amount of time spent in gc.
We also noticed that if the primary heap objects you allocate are large then
G1GC can cause the JVM to report out of heap memory when it has only used 50
percent of the heap. We saw this with tests in which all the geode region
values were larger than 50 percent of the G1 region size. Oracle calls these
"humongous" objects. The default G1 region size is 1m. You can increase it up
to 32m (it is always a power of 2) by using this:
"--J-XX:G1HeapRegionSize=32m". If you are using large values and want to use
G1GC without increasing its RegionSize (or if you large values are bigger than
16m) then you could make your geode regions that will contain the large values
off-heap. But even if you do that the large off-heap values will allocate
temporary large heap values that G1GC will treat as humongous allocations even
though they will be short lived. So consider using CMS if most of you values
will result in humongous allocations.
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