On Thu, 4 Feb 2021 23:23:41 GMT, Chris Plummer <cjplum...@openjdk.org> wrote:
>> Thanks for the thorough list, I have tested most of them but not all. I will >> cover them and update here later. >> >>> So really there are two implementations of heap dumping, one in the VM and >>> one in SA, but a total of 5 ways to get to them. I'm just starting to get >>> my head wrapped around all this myself. We've created a very confusing >>> situation for us, and unfortunately I think some of the changes that got us >>> here was driven by a goal to simply things. >> >> Yes, it makes me even curious about why there can be two different >> implementation of them (one by C++ and one by Java), it seems we need >> double the work of adding new options for those tools, like parallal for >> jmap histo and dump, etc. > > One implementation is in the JVM itself, to be used when the JVM is still > running well, and not just from command line tools. Heap dumping can also be > triggered by the JVM itslef by setting flags like -XX:+HeapDumpBeforeFullGC. > The other implementation is in SA, to be used on a core file or a hung JVM > process, although it can also be used on a JVM that is still running well. > BTW, there used to be a 3rd implementation. The old hprof profiler (a JVMTI > agent) also was used to generate hprof files. Dear @plummercj, > `--dumpfile` and `--gz` can only be used with `--binaryheap`. That should be > made clear in the help text. I added indentation for these two sub-options. > * SA's `jhsdb jmap --binaryheap` (which uses JMap.java with `-heap:format=b`) > * SA's clhsdb `dumpheap` command (which also uses JMap.java with > `-heap:format=b`) > * executing SA's `sun/jvm/hotspot/tools/JMap` class directly > * `jmap -dump` command (Uses Attach API's `heapdump` command, which uses > hotspot `HeapDump` class) > * `GC.heap_dump` dcmd, which also uses the hotspot `HeapDumper` class All 5 commands help message have been tested. ------------- PR: https://git.openjdk.java.net/jdk/pull/1712
