direct_max stats missing on newer JDKs

[ywelsch]

The MaxDirectMemorySize information, which is reported as direct_max in the node info APIs, is no longer correctly reported on newer JDKs. In particular, it's missing with the bundled JDK. The reason is that VM class has moved from the sun.misc to the jdk.internal.misc package, which means that the following lines of code are not working anymore on newer JDKs:

elasticsearch/server/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java

Lines 61 to 62 in 2b8c7c5

	Class<?> vmClass = Class.forName("sun.misc.VM");
	directMemoryMax = (Long) vmClass.getMethod("maxDirectMemory").invoke(null);

[elasticmachine]

Pinging @elastic/es-core-infra

[williamrandolph]

I'm reviewing this issue for the Core/Infra team issue triage. I'd like to discuss whether we should consider removing stats that we can't correctly report from the node info APIs.

Note that the intent of the JDK developers is that classes in jdk.internal should be internal to the JDK and eventually will be made inaccessible. See this comment for details: #42748 (comment)

[williamrandolph]

We discussed this in a team meeting today. We know that we use direct_max size in our ergonomics code, but we get that value by parsing the output of a JVM command, not by using the jdk.internal class directly. If these values are (1) static over the runtime of the application, and (2) something we can derive from a java command, we can find a way to pass them in at startup and report them here.

If one of those conditions is not met for one of these stats, that is, if the value changes or can't be retrieved at start time, then we should deprecate and remove that stat.