A Combiner runs after the Mapper and before the Reducer, it will receive as input all data emitted by the Mapper instances on a given node. It then emits output to the Reducers. So the records of the combiner input should less than the maps ouputs.
12/08/29 13:38:49 INFO mapred.JobClient: Map-Reduce Framework
12/08/29 13:38:49 INFO mapred.JobClient: Reduce input groups=8649
12/08/29 13:38:49 INFO mapred.JobClient: Map output materialized bytes=306210
12/08/29 13:38:49 INFO mapred.JobClient: Combine output records=859412
12/08/29 13:38:49 INFO mapred.JobClient: Map input records=457272
12/08/29 13:38:49 INFO mapred.JobClient: Reduce shuffle bytes=0
12/08/29 13:38:49 INFO mapred.JobClient: Reduce output records=8649
12/08/29 13:38:49 INFO mapred.JobClient: Spilled Records=1632334
12/08/29 13:38:49 INFO mapred.JobClient: Map output bytes=331837344
12/08/29 13:38:49 INFO mapred.JobClient: **Combine input records=26154506**
12/08/29 13:38:49 INFO mapred.JobClient: **Map output records=25312392**
12/08/29 13:38:49 INFO mapred.JobClient: SPLIT_RAW_BYTES=218
12/08/29 13:38:49 INFO mapred.JobClient: Reduce input records=17298