Upgrade from 11 to 17 leads to busy CPU when idle
graphhopper at gmx.de
Tue Dec 20 11:04:56 UTC 2022
I'm sorry in advanced if this is the wrong mailing list, but I think my
issue might be related to ZGC.
The application ran under JDK 11.0.5+10 used -Xmx233g -Xms233g as jvm
parameters and was running fine and stable on Intel Xeon hardware with
256GB RAM and 6 cores. Note that most of the heap for this application
is static and the application itself is fine with a small amount of
memory like 3GB.
When upgrading to JDK 17.0.5+8 we observe that there was a steady load
(3 cores at 15-25%) although the application received no load. Maybe ZGC
tries to reduce the static heap somehow? I tried to tune the JVM with
-XX:+AlwaysPreTouch, -XX:ZFragmentationLimit=80 and/or -XX:-ZProactive
but I wasn't able to fix this. When using -Xloggc it heavily writes new
log entries and is frequently running "Garbage Collection (High Usage)".
The only way to fix this was to increase -Xmx to 243g.
It is surely an unusual use case (large amount of read-only heap and
only a tiny free space), but requiring now nearly 10GB more RAM seems
More information about the zgc-dev