RFR(L) 8237354: Add option to jcmd to write a gzipped heap dump

[Ioi Lam]

Hi Christoph,

This sounds fair. I will remove my objection :-)

Thanks
- Ioi

On 2/25/20 2:21 AM, Langer, Christoph wrote:
> Hi Ioi,
>
>> Ralf and Christoph,
>>
>> I agree that making it easy for the user is important, so dependency on
>> an external program like pgzip will be a hassle.
> Yes ��
>
>> How about implementing the compression in a Java program? Will something
>> like this be too much of a hassle?
>>
>>       jcmd $PID GC.dump -stdout | java -jar HeapDumpZipper.jar > heap.gz
>>
>> This way, we can implement the exact compression algorithm as Ralf
>> described, without making it part of the VM. Writing it in Java probably
>> would be easier to maintain.
>>
>> If it makes sense, we can include the Java code as part of the JDK, so
>> there's no need to ship a separate JAR file to the user.
>>
>>       jcmd $PID GC.dump -stdout | java jdk.internal.heapdump.Zipper >
>> heap.gz
> Well, we definitely would have to enhance hotspot and jcmd to be able to stream the dump data out. And the Java code, doing the compression should also be internalized to jcmd such that piping is not required. It's hard to say whether maintainability will be easier when implementing these parts in Java. However, performance is definitely a thing which has to be considered - I guess doing the zipping in hotspot is better for that. And also the option to support the "heapdump on OOM" scenarios would not be handled here.
>
> Best regards
> Christoph
>