Thank you, Wolfgang. The cause of the problem was that the amount of Java Heap Memory dedicated for a MR container was too low, though there was enough phisycal memory on each node. After some tuning, I found out that the ratio of memory of data (unzipped) to index to available JVM memory for a reducer task is about 2:1. So if you have a larger file to index in single reducer you likely get OutOfMemeryError.   Thanks for the help.  ... View more