Resource Management

JVM Memory Mgmt.

Excellent Article: JVM Memory Settings in a Container Environment

  • MaxHeapSize = MaxRAM * 1 / MaxRAMFraction which by default is only 25%, which could be too low especially on tiny hardware! Keep in mind that besides heap you also need RAM for each thread, plus constant overhead

  • Java 10 introduces XX:+UseContainerSupport (enabled by default) and XX:MaxRAMPercentage (0..100) which is more transparent than

  • Set mem_limit: 360m in docker-compose.yaml to set the container limits, then play around MaxRAMPercentage to end up with a reasonable heap. Make sure to actually pass -XX:MaxRAMPercentage=xxx in Dockerfile e.g. as follows …​

ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -Djava.security.egd=file:/dev/./urandom -jar app.jar" ]

get Heap Info depending on RAMPercentage
# with 25%
$ docker exec angkor-api  java -XX:+PrintFlagsFinal  -XX:MaxRAMPercentage=25 -version | grep -Ei "maxheapsize|maxram"
   size_t MaxHeapSize                              = 132120576                                 {product} {ergonomic}
 uint64_t MaxRAM                                   = 377487360                              {pd product} {ergonomic}
    uintx MaxRAMFraction                           = 4                                         {product} {default}
   double MaxRAMPercentage                         = 25.000000                                 {product} {command line}

# with 40%
$  docker exec angkor-api  java -XX:+PrintFlagsFinal  -XX:MaxRAMPercentage=40 -version | grep -Ei "maxheapsize|maxram"
   size_t MaxHeapSize                              = 150994944                                 {product} {ergonomic}
 uint64_t MaxRAM                                   = 377487360                              {pd product} {ergonomic}
    uintx MaxRAMFraction                           = 4                                         {product} {default}
   double MaxRAMPercentage                         = 40.000000                                 {product} {command line}

# on the container
$ docker inspect angkor-api|grep Memory
            "Memory": 377487360,

# on the host
$ cat /proc/meminfo |grep Mem
MemTotal:         472172 kB
MemFree:           20372 kB
MemAvailable:     132304 kB

Golang Garbage Collection

Go 1.3 Garbage collector not releasing server memory back to system and force debug.FreeOSMemory()