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Your build hit the 4G memory limit

Your build contains a message that says:

Warning: The build VMs have a memory limit of 4G. Your build hit this limit on one or more containers, and your build results are likely invalid.

The reason for this is your builds run in a VM with 4GB of available RAM. If you go over that limit, Linux kills a process, somewhat arbitrarily.

Hitting the RAM limit typically indicates a bug, such as a process not freeing resources.


Builds which run out of memory in this way result in a file being generated called memory-usage.txt, which you will find in the artifacts tab on the build page. This contains information that should help you debug your build.

If memory-usage.txt does not include enough information, you can SSH into your build. Use the SSH button to ssh into a running build and run top.

Hit Shift + M to sort by memory usage and watch what process is using the most memory while your tests run.

The number to pay attention to is the RES (short for resident) column. This tracks the actual RAM used by a process. Note that the 4GB limit applies to the sum of all processes running in your container, not just a single process.

One thing to keep in mind is that the %MEM you see in top is the percentage of the entire machine, not just the container that your builds are running in. The Out-Of-Memory killer typically runs when a process uses up 2-3% of total memory.

Setting memory limits for the JVM

JVM is known to pre-allocate significant amounts of memory in large chunks, which sometimes can result in the OOM errors.

If that is the case for you, you can limit the JVM’s usage of memory by declaring the limits in the JAVA_OPTS environment variable, like this:

    JAVA_OPTS: "-Xms512m -Xmx1024m"

Note that you might want to use different numbers depending on the other processes running during your build. Check the contents of your memory-usage.txt for the memory usage of the rest of the processes and adjust the parameters accordingly.

Out of memory errors in Android builds

Gradle does not respect the JAVA_OPTS variable, so for Android builds you should limit the JVM’s heap by adding the GRADLE_OPTS variable with the following contents to your circle.yml file:

    GRADLE_OPTS: '-Dorg.gradle.jvmargs="-Xmx2048m -XX:+HeapDumpOnOutOfMemoryError"'

Out of memory errors in OCaml/Reason builds

The main tool for configuring space use in OCaml is the space overhead parameter (OCAMLRUNPARAM’s o)

Add export OCAMLRUNPARAM="o=20" before running your program to limit your memory use.

Unlike Java, you don’t specify a maximum heap size but instead a relative overhead: o=80 (the default) means that the heap is allowed to grow to the amount of live data in your program + 80%.

If your tests actually need more than 4GB of RAM, please migrate your project to CircleCI 2.0, see Migration for instructions.