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Choose CMS with the java arg (-XX:+UseConcMarkSweepGC).
(CMS is the default with java 1.8.)
Sizing the Heap
The CMS GC is fairly strict with its allocation of new and old generation heap space. For the Old Generation we need a some score of MB for non-metadata persistent allocations, and enough space for two parses of InCommon metadata—so we can refresh it without triggering a full collection. That's about a minimum of 1.5GB for the old space. The new generation is very dynamic, but the IdP doesn't require large blocks at a time. We could get by with 500MB for the new.
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