The execution speed difference for an MR job with and without a combiner class is huge. The Security log analytics without a combiner class did not complete in 1.5 days. With the addition of a Combiner class, the code finished in 15-20 minutes! Now, the reasons for this performance enhancement are obvious.
- <K, V> are in memory and network latency and traffic to reducers is decreased.
- Disk operations are minimal at the reducers as a result of combine operations.