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From g...@apache.org
Subject [1/2] flink git commit: [FLINK-2883] [docs] Add documentation to forbid key-modifying ReduceFunction
Date Mon, 06 Feb 2017 19:40:04 GMT
Repository: flink
Updated Branches:
  refs/heads/release-1.2 50a0eae91 -> 37d6f8196


[FLINK-2883] [docs] Add documentation to forbid key-modifying ReduceFunction

This closes #3256


Project: http://git-wip-us.apache.org/repos/asf/flink/repo
Commit: http://git-wip-us.apache.org/repos/asf/flink/commit/37d6f819
Tree: http://git-wip-us.apache.org/repos/asf/flink/tree/37d6f819
Diff: http://git-wip-us.apache.org/repos/asf/flink/diff/37d6f819

Branch: refs/heads/release-1.2
Commit: 37d6f8196f12714491c95adb73319bb36e7a0d34
Parents: 57cd071
Author: Greg Hogan <code@greghogan.com>
Authored: Thu Feb 2 16:15:52 2017 -0500
Committer: Greg Hogan <code@greghogan.com>
Committed: Mon Feb 6 13:21:51 2017 -0500

----------------------------------------------------------------------
 docs/dev/batch/dataset_transformations.md | 4 ++++
 1 file changed, 4 insertions(+)
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http://git-wip-us.apache.org/repos/asf/flink/blob/37d6f819/docs/dev/batch/dataset_transformations.md
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diff --git a/docs/dev/batch/dataset_transformations.md b/docs/dev/batch/dataset_transformations.md
index 1bfb87c..1f942d4 100644
--- a/docs/dev/batch/dataset_transformations.md
+++ b/docs/dev/batch/dataset_transformations.md
@@ -279,6 +279,10 @@ element using a user-defined reduce function.
 For each group of input elements, a reduce function successively combines pairs of elements
into one
 element until only a single element for each group remains.
 
+Note that for a `ReduceFunction` the keyed fields of the returned object should match the
input
+values. This is because reduce is implicitly combinable and objects emitted from the combine
+operator are again grouped by key when passed to the reduce operator.
+
 #### Reduce on DataSet Grouped by Key Expression
 
 Key expressions specify one or more fields of each element of a DataSet. Each key expression
is


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