This is not a bug. Chained combiners are not supported for ReduceFunctions yet. :-( I updated the JIRA accordingly.
2015-06-19 13:04 GMT+02:00 Ufuk Celebi <u...@apache.org>: > Hey all, > > on the current master running the WordCount example with a text file > input/output results and a manual reduce function (instead of the sum(1)) > results in a combiner, which is not chained. > > The corresponding issue is here: > https://issues.apache.org/jira/browse/FLINK-2246 > > Can someone please confirm this? If it is an issue, we should fix it soon. > The serialization overhead is noticeable on larger inputs. > > – Ufuk
