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Java Memory Configuration of Promregator

Using your own Memory Configuration

When using the jar file in your own Java Virtual machine (e.g. you are starting Promregator by typing jar -jar promregator.jar [...] your own), or if you are creating your own Docker image, you need to define your own memory configuration.

Currently, there is no sufficient experience with the memory consumption of Promregator. However, as Promregator in essence is quite stateless, only the amount of memory is required to allow handling the number of concurrent requests.

As soon as more experience is available, this documentation will be adjusted.

In the pre-delivered Docker Image

The image provided by Promregator has a fixed memory configuration. As of writing it is configured using the following (memory configuration) parameters:

-XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -Xss600k -XX:ReservedCodeCacheSize=256m -XX:MaxMetaspaceSize=300m

In a nutshell this means:

  • Each thread may allocate a stack having up to 600 kilobytes
  • Metaspace (non-Heap) is limited to 300 megabytes at maximum (but may grow dynamically).
  • There are 256 megabytes (within metaspace) reserved for Code Caching.
  • The rest of the memory, which is granted via the cgroup (e.g. the memory which you grant to the container), is used for the heap.

These are standard values which should permit Promregator to run in most of the usual environments properly.

Given this memory configuration, a maximal memory allocation for the Docker container of 700 megabytes shall be enough for Promregator to run properly. With issue #66 we have seen that granting only 512 megabytes to the container is not enough to permit Promregator run properly.

If you want influence the memory configuration directly, you are able to define your own set of memory configuration parameters by providing an own configuration in the environment variable JAVA_MEM_OPTS. Assuming that you wanted to set the maximal heap memory size to 400 megabytes (while leaving all other configuration parameters unchanged), you would have to start the Docker container like this:

$ docker run -d -m 800m --env JAVA_MEM_OPTS="-Xmx400m -Xms300m -Xss600k -XX:ReservedCodeCacheSize=256m -XX:MaxMetaspaceSize=300m" promregator/promregator:0.x.y [...]

Note that all other parameters still need to be provided, as setting JAVA_MEM_OPTS externally disables any kind of defaulting.

Monitoring Memory Consumption of Promregator

Having attached Prometheus to Promregator, you are also able to monitor the memory consumption of Promregator. For instance, the following metrics might be of interest for you:

  • promregator_jvm_memory_bytes_used{area="heap"} provides the amount of memory allocated for the heap
  • promregator_jvm_memory_bytes_used{area="non-heap"} provides the amount of memory allocated for the non-heap part (i.e. Metaspace)

Note that Java is running a garbage collector; thus, old and unused objects may still be reported (for example) to consume memory on the heap, because they have not been cleaned up, yet. If you want to see when garbage collection has taken place, please refer to promregator_jvm_gc_collection_seconds_count. You may also gain further insight on the different memory areas subject to garbage collecting by looking at promregator_jvm_memory_pool_bytes_used.