DumpJFR tool

[Erik Gahlin]

On 2019-10-24 16:52, Yasumasa Suenaga wrote:
> On 2019/10/24 22:50, Erik Gahlin wrote:
>> Hi Yasumasa,
>>
>> The DumpJFR tool relied on SA, which was too much of a burden to 
>> maintain (slowing down the development of new JFR features).
>>
>> I think tool was removed in Oracle JDK 9, at least it was completely 
>> broken at that time.
>>
>> Functionality has been added that allows JFR to dump an emergency 
>> dump if the JVM crashes. This reduces the need for a separate tool.
>
> SA is powerful tool for hung up and for postmortem analysis.
> For example, SA is only way to gather any information even if Attach 
> Listener does not respond.
>
There are always trade-offs, and with the crash dump support in place, 
we came to the conclusion that the cost of maintaining the tool and SA 
support outweighed the benefits.

> JFR emergency dump is not enough.
> I commented in JDK-8213435, crash which is caused by 
> -XX:+CrashOnOutOfMemoryError does not contain
> recently old object sampling.
Duplicating logic in the SA tool to calculate shortest path GC, 
information about root objects etc. would be a much larger effort to 
implement and maintain than fixing JDK-8213435.

> In addition, there are some cases not to be called crash handler (e.g. 
> native stack overflow).
>
>
>> The Event Streaming JEP, targeted for JDK 14, should also help out 
>> here, as it ensures the latest file in the disk repository, 
>> previously known as the .part file, can always read. With a default 
>> flush interval of 1 second, data will be available very close to the 
>> point of the crash.
>
> Is flight record flushed to the disk without any programming for Event 
> Streaming?
> I guess it is just about Event Stream API.
>
> I hope to get flight record with some configuration - not any 
> programming.

Streaming will be always on. No programming or configuration will be needed.

You can just open the latest file in JMC.

Best regards,
Erik

>
>
> Thanks,
>
> Yasumasa
>
>
>> Best regards,
>> Erik
>>
>>> Hi all,
>>>
>>> DumpJFR tool is introduced in JDK 8u60 [1], however it is not 
>>> available on OpenJDK (JDK 11 or later).
>>> Why it is not open sourced?
>>>
>>> I think DumpJFR is very useful not only for postmortem analysis but 
>>> also analyzing process hung up.
>>> If DumpJFR is available on OpenJDK, I believe JFR will be more 
>>> useful for troubleshooting.
>>>
>>>
>>> Thanks,
>>>
>>> Yasumasa
>>>
>>>
>>> [1] 
>>> https://www.oracle.com/technetwork/java/javase/8u60-relnotes-2620227.html
>>