RFR: 8256450: Add gz option to jmap to write a gzipped heap dump [v2]

[Chris Plummer]

On Wed, 18 Nov 2020 01:22:08 GMT, Lin Zang <lzang at openjdk.org> wrote:

> And the old jmap -dump can not accept "gz" option, it fails with error message printed, no matter what jvm version it work with.

I just want to clarify what I was referring to. I was not talking about trying to use gz with the old jmap command (from the command line). I was asking what happens if you use the old jmap command on a newer jvm that does support (and I assume expects) the new "compression level" argument to be passed, but it won't be. We've had this issue before. See [JDK-8219721](https://bugs.openjdk.java.net/browse/JDK-8219721). I haven't had a chance to look at the fix for JDK-8219721 to see if it also solves the issue with this change, or if something similar also needs to be done with this change.

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PR: https://git.openjdk.java.net/jdk/pull/1251