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I faced an interesting problem trying to analyze a memory consumption in my Java application running on docker container vs host machine.
On the host I'm using Yourkit tool to analyze a memory consumption.
For docker container docker stats <docker id/name>
What I'm getting is that on MAC yourkit shows me 50M Non-heap size + ~40M heap size, in total ~100M
Whereas, when I deploy and run the same war on a container, the stats shows me 200M
CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
879fb113ca8d jetty-app 0.19% 214.6MiB / 1.952GiB 10.74% 1.49MB / 88.9kB 31.7MB / 6.42MB 29
Can anyone shed some light on this phenomenon?
Assuming that stats provides wrong results, I tried to limit the memory on a container using --memory flag doesn't help much, I'm getting OOM.
Thanks in advance
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Java Virtual Machine optimizes the code during runtime. Again, to know which parts to optimize it needs to keep track of the execution of certain code parts. So again, you are going to lose memory.
Docker Container Memory Limits - Set global memory limit By default, the container can swap the same amount of assigned memory, which means that the overall hard limit would be around 256m when you set --memory 128m . I quickly create a diagram to explain how both values relate to each other.
Docker can enforce hard memory limits, which allow the container to use no more than a given amount of user or system memory, or soft limits, which allow the container to use as much memory as it needs unless certain conditions are met, such as when the kernel detects low memory or contention on the host machine.
You might want to try and measure again, with an openJDK 8u212 or more (April, 16th 2019). (no Oracle JDK, since their license has changed)
See "Docker support in Java 8 — finally!" from Grzegorz Kocur.
Now:
There is no need to use any hacky workarounds in a docker entrypoint, nor setting Xmx as fixed value anymore.
Docker support was also backported to Java 8.
Let’s check the newest openjdk image tagged as 8u212. We’ll limit the memory to 1G and use 1 CPU:docker run -ti --cpus 1 -m 1G openjdk:8u212-jdk
You can fine-tune the heap-size with new flags (already present in Java 10+, but now back ported to Java 8), and explained here.
-XX:InitialRAMPercentage
-XX:MaxRAMPercentage
-XX:MinRAMPercentage
If for some reason the new JVM behaviour is not desired it can be switched off using -
XX:-UseContainerSupport.
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