G1gc compaction algorithm

[Martin Makundi]

Hi!

I tried the new parameters:


>  Based on this one, can you do one with -XX:G1MaxNewSizePercent=30
> -XX:InitiatingHeapOccupancyPercent=20 added?
>

This seems to hang the whole system.... we have lots of mostly short lived
(ehcache timeToIdleSeconds="900") large java object trees 1M-10M each (data
reports loaded into cache).

Maybe eden should be even bigger instead of smaller?

Here is the log from today, it hung up quite early, I suspect the gc:
http://81.22.250.165/log/gc-16m-2014-08-12.log

The process ate most of the cpu cacacity and we had to kill it and restart
without -XX:G1MaxNewSizePercent=30.

What you suggest?

**
Martin


> The reason for G1MaxNewSizePercent(default=60) is to set an upper limit to
> Eden size.  It seems the Eden size grows to 17g before Full gc, then a
> bunch of humongous allocation happened, and there is not enough old gen.
>
> The following log entry seems not right: The Eden Size is over 60% of the
> heap.
> "2014-08-11T11:13:05.487+0300: 193238.308: [GC pause (young)
> (initial-mark) 193238.308: [G1Ergonomics (CSet Construction) start choosing
> CSet, _pending_cards: 769041, predicted base time: 673.25 ms, remaining
> time: 326.75 ms, target pause time: 1000.00 ms] 193238.308: [G1Ergonomics
> (CSet Construction) add young regions to CSet, eden: 1 regions, survivors:
> 21 regions, predicted young region time: 145.63 ms] 193238.308:
> [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 1 regions,
> survivors: 21 regions, old: 0 regions, predicted pause time: 818.88 ms,
> target pause time: 1000.00 ms], 0.7559550 secs]   [Parallel Time: 563.9 ms,
> GC Workers: 13]      [GC Worker Start (ms): Min: 193238308.1, Avg:
> 193238318.0, Max: 193238347.6, Diff: 39.5]      [Ext Root Scanning (ms):
> Min: 0.0, Avg: 13.0, Max: 35.8, Diff: 35.8, Sum: 168.4]      [Update RS
> (ms): Min: 399.2, Avg: 416.8, Max: 442.8, Diff: 43.6, Sum: 5418.0]
> [Processed Buffers: Min: 162, Avg: 232.0, Max: 326, Diff: 164, Sum:
> 3016]      [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum:
> 0.1]      [Object Copy (ms): Min: 79.9, Avg: 104.8, Max: 152.4, Diff: 72.5,
> Sum: 1363.0]      [Termination (ms): Min: 0.0, Avg: 19.1, Max: 27.3, Diff:
> 27.3, Sum: 248.9]      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0,
> Diff: 0.0, Sum: 0.3]      [GC Worker Total (ms): Min: 524.1, Avg: 553.8,
> Max: 563.7, Diff: 39.6, Sum: 7198.8]      [GC Worker End (ms): Min:
> 193238871.7, Avg: 193238871.8, Max: 193238871.8, Diff: 0.1]
>    [Code Root Fixup: 0.0 ms]
>    [Clear CT: 0.3 ms]
>    [Other: 191.7 ms]
>       [Choose CSet: 0.0 ms]      [Ref Proc: 190.1 ms]      [Ref Enq: 0.3
> ms]      [Free CSet: 0.2 ms]
>    [Eden: 16.0M(2464.0M)->0.0B(22.9G) Survivors: 336.0M->240.0M Heap:
> 14.1G(28.7G)->14.1G(28.7G)]
>  [Times: user=8.45 sys=0.04, real=0.75 secs]"
>
> The reason for increasing InitiatingHeapOccupancyPercent to 20 from 10 is
> we are wasting some concurrent cycles.
>
> We will see how this goes.  We might increase G1ReservePercent to handle
> this kind of allocation if it is not enough.
>
> Thanks,
> Jenny
>
> Thanks,
> Jenny
>
> On 8/11/2014 10:46 AM, Martin Makundi wrote:
>
> Hi!
>
> Here is our latest log with one Full GC @ 2014-08-11T11:20:02 which is
> caused by heap full and allocation request: 144 bytes.
>
>  http://81.22.250.165/log/gc-16m-2014-08-11.log
>
>  Any ideas how to mitigate this kind of situation? The Full GC makes
> quite a difference to the situation but causes a painful pause also.
>
>  **
> Martin
>
>
>
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