Build failing due to OOM but works fine locally with same constraints.

I have been running a maven build locally using the guide provided here. The build works perfectly in a local environment but fails (mostly) on bitbucket due to OOM. I see following error in the logs:

#!bash

[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.6.0:exec (mvn-package-for-python-test) on project demo-python: Command execution failed. Process exited with an error: 137 (Exit value: 137) -> [Help 1]

With error code 137 showing that the process was killed forcefully. Is there any other resource constraint that the provided guide is missing or the 4G memory support isn't really 4G?