Long time back, I built an extension, by which you can take the openrefine mappings, and run on a hadoop cluster. The idea is you would run all transformations on a small dataset on your local machine. Once you are satisfied with the mappings, you would deploy the same on hadoop cluster. I have tested this on large datasets, and it works. Let me know how I can help. You can check my github: https://github.com/rmalla1/OpenRefine-HD