GcInfo: longest pause duration?

[David Holmes]

Hi Paul,

Probably best to also include the GC mailing list here.

David

On 24/10/2017 2:31 AM, Hohensee, Paul wrote:
> I’d like to solicit opinions on reporting GC pause duration 
> (stopped-world pause time) via JMX. This info would be useful in 
> figuring out whether or not GC pause times are factors in failing to 
> meet response time SLAs. The info is of course available directly from 
> GC logs, but parsing logs is fraught and JMX doesn’t seem to report the 
> equivalent info.
> 
> GcInfo
> 
> https://docs.oracle.com/javase/9/docs/api/com/sun/management/GcInfo.html
> 
> has a getDuration() method which works fine for the non-concurrent 
> collectors (since they’re STW), but for CMS and G1 it appears to report 
> the duration of an entire concurrent cycle, which isn’t what I want. The 
> number of STW pauses during a concurrent cycle varies by collector, so 
> ideally there would be a method that reports cause (as a string) and 
> duration for each STW pause. If that’s too much, perhaps the minimum 
> might be a getMaxPauseDuration() method that reports the maximum pause 
> duration of all the STW pauses that happen during a concurrent cycle.
> 
> Relatedly, the full compacting GCs that happen as a result of CMS and G1 
> concurrent mode failure aren’t reported separately from concurrent 
> cycles. It would be useful to differentiate these from 
> “ConcurrentMarkSweep” and “G1 Old Generation”. Perhaps add collector 
> types to CMS and G1, vis. “MarkSweepCompact” (which already exists and 
> is literally what’s executed by CMS) and a new “G1 MarkSweepCompact” 
> collector for G1.
> 
> If there’s a consensus that something should be done about either of 
> these issues, I’d be happy to file RFE(s) and do the work.
> 
> Thanks,
> 
> Paul
>