How to set heap size for sbt?

You need SBT_OPTS, here’s what I use in my .bash_profile:

export SBT_OPTS="-Xmx1536M -XX:+UseConcMarkSweepGC -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=2G -Xss2M  -Duser.timezone=GMT"

UPDATE:
To get your 2G heap space you can use this:

export SBT_OPTS="-Xmx2G -XX:+UseConcMarkSweepGC -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=2G -Xss2M  -Duser.timezone=GMT"

NOTE: SBT MUST BE LATEST VERSION

Older versions of sbt contain bugs that override these settings, use brew upgrade sbt for latest sbt for Mac (assuming brew install) (IDK for Linux). https://github.com/sbt/sbt/issues/2945#issuecomment-277490848