On Tue, 17 Nov 2020 18:57:10 GMT, Chris Plummer <[email protected]> wrote:
>> Lin Zang has updated the pull request incrementally with one additional >> commit since the last revision: >> >> revise the uintx format issue for output message > > Are the Attach API changes backwards compatible? You've added a new arg, but > that arg could be passed to an older JVM that doesn't support it (I think it > just gets ignored), or an older JVM would fail to pass the arg to a new JVM > that is expecting it. > > Also, please see my comments in > [JDK-8256451](https://bugs.openjdk.java.net/browse/JDK-8256451) regarding SA > heap dumping support, and how it will lack this ability to compress the heap > dump. Hi @plummercj, Thanks for your comments! > Are the Attach API changes backwards compatible? You've added a new arg, but > that arg could be passed to an older JVM that doesn't support it (I think it > just gets ignored), or an older JVM would fail to pass the arg to a new JVM > that is expecting it. Correct, the new "jmap -dump:gz=1 [pid]" could work with old JVM and the "gz" option is ignored. 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 also tested that jcmd GC.heap_dump command with old version of jcmd can not accept the option "-gz=[number]". Moreover, This behavior is similar to "parallel=<num>" option recently added to jmap -histo. So IMHO the risk is not high. If the "gz" option is not used, jmap -dump could work normally, with different version of jmap command and JVM. (I only tested with jdk8, jdk11 and latest jdk build) > Also, please see my comments in > [JDK-8256451](https://bugs.openjdk.java.net/browse/JDK-8256451) regarding SA > heap dumping support, and how it will lack this ability to compress the heap > dump. Yes, I am also considering adding compression support to them, but I am not sure whether there should be new CSR issues created separately to tracking them, and whether I should create those issues at present because I am only planing the work. Let's discuss in the CSR. Thanks! BRs, Lin ------------- PR: https://git.openjdk.java.net/jdk/pull/1251
