Does the Java G1 garbage collector (as implemented in Open JDK) respect the -XX:MaxHeapFreeRatio=n JVM parameter?
Does it respect it in Java 8?
I found JEP 346: Promptly Return Unused Committed Memory from G1 delivered in Java 12, but it's not clear to me what was the state before it.
A non-authoritative answer that I found is based on https://bugs.openjdk.java.net/browse/JDK-8078039?focusedCommentId=13632717&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-13632717
Most notably, some GCs support it, some do not. This RFE doesn't say which GC is used, so I assume we are talking about the default GC which supports MaxHeapFreeRatio. G1 also supports this option.
To shrink the heap (and release memory) a full GC is required. It the application doesn't trigger a full GC manually, it may take a while before one is triggered by the JVM.
So the answer would be (for Java 8): yes... but no.
(I remain curious whether there is a more authoritative source and what's the current state, in more modern JVMs)
I do not know a more authoritative answer than the source code and yes, you are correct in your answer - the release of the memory will happen only after a Full GC (at least before that JEP).
For java-8:
That argument does matter, look here for example.
That code is not very complicated to understand, and here is the actual shrink that happens.
For a much more extensive answer (regarding java-11, but still qualifies to java-8), read this.
The bottom-line is that - that flag does matter, but how exactly is implementation dependent. There is no simple answer to your question.
