SBT out of memory with subprojects

Question

We're using SBT 0.13 and a Java 8 JVM on CircleCI to build a Play application with several subprojects. We were occasionally getting out of memory issues on CircleCI, where it aborted our build because it exceeded 4 GB of memory usage.

Yesterday, I added a new subproject to our build, and almost all builds fail now on the out of memory issue. It looks like adding subprojects also adds to the amount of memory used for our build.

I've tried several things to reduce our memory load:

• Add _JAVA_OPTIONS: "-Xms512m -Xmx2048" to circle.yml as described on CircleCI's documentation pages. (I noticed from the log that the JVM does pick up on this setting.)
• Add a -mem parameter to the SBT call.
• Add concurrentRestrictions in Global += Tags.limit(Tags.Test, 1) to the top of the SBT file, to make sure that at least the memory isn't used all at once.

All of these measures seemed to have helped, but I haven't found the definitive solution to this problem yet.

What else can I do to keep SBT's memory usage under control?

EDIT: Our project has 5 subprojects, with about 14000 lines of Scala code (and also, 21000 lines of Java code that we 'inherited'). The out-of-memory usually (but not always) occurs while executing static analysis using FindBugs: we use that in conjunction with the FindSecurityBugs plugin to find security issues.

Answer 1

There two concerns here that are getting mixed:

1. Circle CI not picking up values for memory limits

2. SBT using an excessive amount of memory

The first issue has to be addressed looking at CircleCI documentation / examples. To investigate why you use so much memory, you can run your sbt locally with memory limits lower than the 4g (i.e. 2g). You will find yourself in one of these two cases:

1. Your tests are really using too much memory, maybe because of memory leaks. Your JVM exits because of an java.lang.OutOfMemoryError: GC overhead limit exceeded. You should run the build locally with a profiler and see what's causing you problem (database connections not closed?)

2. Your tests are using too much memory due to SBT ability to re-load classes dynamically: in SBT is it possible to re-load class completely inside the same JVM (i.e. for example you can launch console, load the class, edit the file, recompile and relaunch console and re-load the class). As described in the Oracle documentation here, there is no limit for the Maximum MetaSpace in Java 8 and you should set one so that your heap + metaspace < 4gb. See https://blogs.oracle.com/poonam/entry/about_g1_garbage_collector_permanent