databricks has a page that describes the pitfalls: https://databricks.gitbooks.io/databricks-spark-knowledge-base/content/best_practices/prefer_reducebykey_over

databricks has a page that describes the pitfalls: https://databricks.gitbooks.io/databricks-spark-knowledge-base/content/best_practices/prefer_reducebykey_over_groupbykey.html https://databricks.gitbooks.io/databricks-spark-knowledge-ba... I don't know if the OutOfMemory exception can still occur in recent versions of Spark, but the performance impact of groupByKey is very real.