Well this is a Java only way of telling that you allow the Java VM to allocate more Heap memory... its not Mac specific.
Sometimes when the heap fills up close to its limits the Java VM has to do a lot cleanup processing and can become slow... not sure if this is a memory leak or just a higher heap usage in the latest release. Apperently VMs on different plattforms can deal more or less good with this situation.

The crash you posted is most likely not Phex related, most crashes are due to Java bug or incompatibilities with driver, os libraries or these things..

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