With JVM inlining enabled, profiles of Terasort run show more than 3% time spent in MapTask$MapOutputBuffer.compare( ) method in each of the Map JVMs. In this particular configuration there are 8 Map JVMs. So a big chunk of time is spent in this particular method. With JVM inlining disabled, java.nio.Bits.getIntB( ), java.nio.HeapByteBuffer.get( ) and MapTask$MapOutputBuffer.compare( ) methods become hot spots in that order. Looking at the code for compare( ) method above observations make sense.
I would appreciate if someone could explain what exactly is the role of the compare( ) method. May be there is some config property which would reduce the number of times this method gets called? Thanks for your time. -Shrinivas
