In the referenced blog is this:
"Btw, it seems like this is the only way to have certain JVM options such as -verbose:gc (although using JConsole may be a better choice) defined in domain.xml to show up at all."
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That's because all diagnostic output generated by the JVM itself will go into the 'jvm.log' file rather than 'server.log'. This is also where thread dumps go.
You can find jvm.log in the same directory as server.log
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