G1 feedback: adaptive size problems ?

[Simone Bordet]

Hi,

using JDK 1.7.0_04, Ubuntu Linux 12.04 64 bit, attached you can find
the GC log of my Java IDE.

Startup options:

-Xmx1024m
-Xms1024m
-Xmn512m
-XX:+UseG1GC
-XX:MaxGCPauseMillis=200
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:MaxPermSize=256m
-XX:ReservedCodeCacheSize=64m
-ea

I noticed that sometimes G1 performs a "to-space overflow" collections
that last way more than the target pause (in my case, up to 3+
seconds), and that after these kind of pauses the survivor spaces get
a big size reduction (e.g from 64 MiB to 6 MiB), which causes more
"to-space overflow" collections until a Full GC seems to restore
normal conditions.

At one point I see in the log this entry:

   [Eden: 0B(512M)->0B(512M) Survivors: 0B->0B Heap: 1002M(1024M)->1002M(1024M)]

which seems quite odd to me (no young generation ?) and after that a
Full GC that restores everything (at the cost of 1-2 seconds pause).

I'm going to add -XX:-UseAdaptiveSizePolicy which in the past seemed
to solve these issues.

I just wanted to report my findings, and if someone can shed a light
on what's going on, will be great.

Thanks !

Simon
-- 
http://cometd.org
http://intalio.com
http://bordet.blogspot.com
----
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless.   Victoria Livschitz
-------------- next part --------------
A non-text attachment was scrubbed...
Name: g1.log.gz
Type: application/x-gzip
Size: 102917 bytes
Desc: not available
URL: <https://mail.openjdk.org/pipermail/hotspot-gc-dev/attachments/20120430/c7fc9efc/g1.log.gz>