RFR: JDK-8327769: jcmd GC.heap_dump without options should write to location given by -XX:HeapDumpPath, if set [v10]

[Thomas Stuefe]

On Wed, 27 Mar 2024 13:44:42 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> Currently jcmd command GC.heap_dump only works with an additionally provided file name.
>> Syntax : GC.heap_dump [options] <filename>
>> 
>> In case the JVM has the XX - flag HeapDumpPath set, we should support an additional mode where the <filename> is optional.
>> In case the filename is NOT set, we take the HeapDumpPath (file or directory);
>> 
>> new syntax :
>> GC.heap_dump [options] <filename> .. has precedence over second option
>> GC.heap_dump [options] …in case -XX: HeapDumpPath=p is set
>> 
>> This would be a simplification e.g. for support cases where a filename or directory is set at JVM startup with -XX: HeapDumpPath=p and writing to the path is intended/recommended for usage also in the jcmd case.
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   adjust java.1 man page

To weight in on the side of this patch, in most customer scenarios I have seen, there is just one location for heap dumps. Using the same location for OOM and for manual heap dumps seems logical to me.

@dholmes-ora 
> Notwithstanding that there may be cases where this change would be convenient, I really don't like this coupling between the jcmd behaviour and a -XX flag that is intended for something else. It doesn't completely mesh with the jcmd usage and other options, and the documentation story is quite complicated.

Wouldn't this just be a case of changing a flag description? As luck has it, the flag already has a generic name that is not tied to OOMs.

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PR Comment: https://git.openjdk.org/jdk/pull/18190#issuecomment-2024535044