While counting commutative 311 reason codes, engineers want fewer bytes crossing the network during shuffle. Which optional MapReduce idea helps?
Select an answer to reveal the explanation.
Short Explanation
A combiner is like totaling each clerk's sticky notes at their own desk before the courier run. Local pre-sums cut how much crosses the network when the math is commutative. It is optional polish, not a new storage system.
Full Explanation
A combiner is an optional map-side optimization that applies a reduce-like function locally to intermediate outputs. For commutative and associative aggregations such as counts, that shrinks shuffle volume. Combiners do not replace HDFS replication policy, cluster topology, or NameNode design; they only reduce bytes moved when semantics allow.