The system does very little swapping, both when it's GC'ing and when
it's not. Less than 100MB worth of swap is taken.
Giving Tomcat its own HW is not an option at this time, especially as
there's no guarantee it'll solve the problem. Besides it would be a VM
anyway, not physical dedicated HW. The current server is also a VM.
On 15-Nov-16 10:55 PM, Zdeněk Henek wrote:
I would start with moving this tomcat to its own hw.
Did you check swap? This long pauses could be because part of your heap is
swapped to hdd
Regards,
Zdenek Henek
On Tue, Nov 15, 2016, 21:37 George I. Develekos <gdevele...@omilia.com>
wrote:
On 15-Nov-16 10:22 PM, Christopher Schultz wrote:
George,
On 11/15/16 10:46 AM, George I. Develekos wrote:
Hello guys,
We are having problems on a production system with very long "full
GC" times, as long as1200sec real time (!!!).
We are using Java 6 (stuck with CentOS 5.8 at this time) and Tomcat
7.0.64.
Xmx is 5G, Xms is 2G, and GC options are -XX:+UseConcMarkSweepGC
-XX:+CMSIncrementalMode
No other custom memory-related settings are in place.
Looking at the GC log, the last few Full-GC entries are:
1367.020: [Full GC 1367.020: [CMS: 1178831K->527456K(1926784K),
2.1117220 secs] 1250378K->527456K(2080128K), [CMS Perm :
169762K->56187K(169984K)] icms_dc=0 , 2.1118160 secs] [Times:
user=1.96 sys=0.13, real=2.11 secs]
2579.317: [Full GC 2579.317: [CMS2581.876: [CMS-concurrent-mark:
2.558/1212.733 secs] [*Times: user=113.05 sys=28.01,
real=**1212.49 **secs] ** * 3539.969: [Full GC 3539.969:
[CMS3540.056: [CMS-concurrent-sweep: 1.571/23.223 secs] [Times:
user=6.12 sys=1.36, real=*23.21 secs*]
4070.456: [Full GC 4070.457: [CMS: 1252569K->591200K(1926784K),
2.3447040 secs] 1270617K->591200K(2080128K), [CMS Perm :
169983K->56598K(169984K)] icms_dc=0 , 2.3448140 secs] [Times:
user=2.18 sys=0.14, real=2.34 secs]
What can we do?
1367.020 Full GC duration=2.11s
2579.317 Full GC duration=1212.49s
So your full GC immediately started another full GC that took 20 minutes
?
Are you only showing certain FULL GC activity from your log, or is
that everything?
CMS should have a mark and then a sweep each time, but your times
don't seem to add up.
also note that the whole point of CMS is that there isn't any
stop-the-world during the mark portion of the process.
Are you actually experiencing a problem, or are you just suffering
from instrumentor's remorse?
- -chris
Chris,
What I listed is the result of the command:
grep "Full GC" gc.log
So (obviously) I have skipped other GC activity, i.e. whatever GC
activity didn't include the "Full GC" string.
Yes we are having app trouble due to the GC delays so this is a real
problem. Our application has real-time constraints so the GC delays
cannot be tolerated. I selected those GC options _in order to avoid
_long GC times.
Additionally, these periods coincide with high CPU for that JVM
process. From 5-20% CPU where it is normally, it jumps to 60% ore more.
Once GC is done, our app rushes to catch up with tasks that had to wait
for GC to finish.
Answering another question from a member who has kindly responded, yes
the server is running other stuff. Basically it runs three tomcats, the
main one being this one. It also runs a DB2 database that has
close-to-zero activity.
George
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