Zahid Qureshi Thoroughly Inspects the HotSpot JVM Options
While the HotSpot JVM provides developers with a powerful set of JVM options, the documentation that's provided for the options is, in the words of Zahid Qureshi, "criminally short and non-comprehensive." However, Zahid isn't one to simply complain and walk away. Instead, he took the time to thoroughly investigate the HotSpot JVM options, and he presents the results of his study and analysis in his recent blog post, "Inspecting HotSpot JVM Options."
Zahid notes that
The JVM options themselves can be controlled in a number of ways:
- via the command line on JVM startup.
- via JMX for certain options where this is allowed.
- indirectly via the command line by a super-option which then sets other options.
- automatically by the JVM. The JVM has ergonomic capability to detect features of the host and set options accordingly.
Using the first two methods we are explicitly setting options ourselves and can easily track what value each option has (true, false, 20, 100 etc).
Zahid goes on to describe and demonstrate the key options, talks about client versus server JVM analysis, and investigates the "super-option"
-XX:+AggressiveOpts, before concluding:
There is enormous scope for coarse and fine grained control of JVM behaviour. The option
-XX:+PrintFlagsFinalallows comprehensive reporting of the options and their values. The available options vary by build and JVM type (server or client). Recording and auditing this output is an important step in any Java benchmarking or continuous monitoring exercise. Oracle can surreptitiously enable options in new Java builds which may cause inexplicable changes in performance and behaviour of existing applications.
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