Minor GC difference Java 7 vs Java 8

[Chris Hurst]

Hi,

 Has anyone seen anything similar to this ...

On java 6 (range of versions 32bit Solaris) application , using parallel old gc, non adapative.  Using a very heavy test performance load we see minor GC's around the 5ms mark and some very rare say 3or4 ish instances in 12 hours say 20ms pauses the number of pauses is random (though always few compares with the total number of GC's) and large ~20ms (this value appears the same for all such points.) We have a large number of minor GC's in our runs, only a  full GC at startup. These freak GC's can be bunched or spread out and we can run for many hours without one (though doing minor GC's).

What's odd is that if I use Java 7 (range of versions 32bit) the result is very close but the spikes (1 or 2 arguably less) are now 30-40ms (depends on run arguably even rarer). Has anyone experienced anything similar why would Java 7 up to double a minor GC / The GC throughput is approximately the same arguably 7 is better throughput just but that freak minor GC makes it usable due to latency.

In terms of the change in spike height (20 (J6)vs40(J7)) this is very reproducible though the number of points and when they occur varies slightly. The over all GC graph , throughput is similar otherwise as is the resultant memory dump at the end. The test should be constant load, multiple clients just doing the same thing over and over.

Has anyone seen anything similar, I was hoping someone might have seen a change in defaults, thread timeout, default data structure size change that would account for this. I was hoping the marked increase might be a give away to someone as its way off our average minor GC time.

We have looked at gclogs, heap dumps, processor activity, background processes, amount of disc access, safepoints etc etc. , we trace message rate into out of the application for variation, compare heap dumps at end etc. nothing stands out so far.

Chris 





 

 		 	   		  
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