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https://issues.apache.org/jira/browse/FLINK-2398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14658782#comment-14658782
]
ASF GitHub Bot commented on FLINK-2398:
---------------------------------------
Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/988#discussion_r36347244
--- Diff:
flink-staging/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/transformations/CoFeedbackTransformation.java
---
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.flink.streaming.api.transformations;
+
+import com.google.common.collect.Lists;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.streaming.api.operators.StreamOperator;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * This represents a feedback point in a topology. The type of the
feedback elements must not match
+ * the type of the upstream {@code StreamTransformation} because the only
allowed operations
+ * after a {@code CoFeedbackTransformation} are
+ * {@link
org.apache.flink.streaming.api.transformations.TwoInputTransformation
TwoInputTransformations}.
--- End diff --
what's the issue? :smile:
> Decouple StreamGraph Building from the API
> ------------------------------------------
>
> Key: FLINK-2398
> URL: https://issues.apache.org/jira/browse/FLINK-2398
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
>
> Currently, the building of the StreamGraph is very intertwined with the API
> methods. DataStream knows about the StreamGraph and keeps track of splitting,
> selected names, unions and so on. This leads to the problem that is is very
> hard to understand how the StreamGraph is built because the code that does it
> is all over the place. This also makes it hard to extend/change parts of the
> Streaming system.
> I propose to introduce "Transformations". A transformation hold information
> about one operation: The input streams, types, names, operator and so on. An
> API method creates a transformation instead of fiddling with the StreamGraph
> directly. A new component, the StreamGraphGenerator creates a StreamGraph
> from the tree of transformations that result from program specification using
> the API methods. This would relieve DataStream from knowing about the
> StreamGraph and makes unions, splitting, selection visible transformations
> instead of being scattered across the different API classes as fields.
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