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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9877) Add separate docs page for different join types in DataStream API
Date Tue, 31 Jul 2018 10:28:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16563440#comment-16563440
] 

ASF GitHub Bot commented on FLINK-9877:
---------------------------------------

florianschmidt1994 commented on a change in pull request #6407: [FLINK-9877][docs] Add documentation
page for different datastream joins
URL: https://github.com/apache/flink/pull/6407#discussion_r206474587
 
 

 ##########
 File path: docs/dev/stream/operators/joining.md
 ##########
 @@ -0,0 +1,284 @@
+---
+title: "Joining"
+nav-id: streaming_joins
+nav-show_overview: true
+nav-parent_id: streaming_operators
+nav-pos: 11
+---
+<!--
+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.
+-->
+
+* toc
+{:toc}
+
+# Window Join
+A window join joins the elements of two streams that share a common key and lie in the same
window. These windows can be defined by using a [window assigner]({{ site.baseurl}}/dev/stream/operators/windows.html#window-assigners)
and are evaluated on elements from both of the streams.
+
+The elements from both sides are then passed to a user-defined `JoinFunction` or `FlatJoinFunction`
where the user can emit results that meet the join criteria.
+
+The general usage can be summarized as follows:
+
+{% highlight java %}
+stream.join(otherStream)
+    .where(<KeySelector>)
+    .equalTo(<KeySelector>)
+    .window(<WindowAssigner>)
+    .apply(<JoinFunction>)
+{% endhighlight %}
+
+Some notes on semantics:
+- The creation of pairwise combinations of elements of the two streams behaves like an inner-join,
meaning elements from one stream will not be emitted if they don't have a corresponding element
from the other stream to be joined with.
+- Those elements that do get joined will have as their timestamp the largest timestamp that
still lies in the respective window. For example a window with `[5, 10)` as its boundaries
would result in the joined elements having 9 as their timestamp.
+
+In the following section we are going to give an overview over how different kinds of window
joins behave using some exemplary scenarios.
+
+## Tumbling Window Join
+When performing a tumbling window join, all elements with a common key and a common tumbling
window are joined as pairwise combinations and passed on to a `JoinFunction` or `FlatJoinFunction`.
Because this behaves like an inner join, elements of one stream that do not have elements
from another stream in their tumbling window are not emitted!
+
+<img src="{{ site.baseurl }}/fig/tumbling-window-join.svg" class="center" style="width:
80%;" />
+
+As illustrated in the figure, we define a tumbling window with the size of 2 milliseconds,
which results in windows of the form `[0,1], [2,3], ...`. The image shows the pairwise combinations
of all elements in each window which will be passed on to the `JoinFunction`. Note that in
the tumbling window `[6,7]` nothing is emitted because no elements exist in the green stream
to be joined with the orange elements ⑥ and ⑦.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+import org.apache.flink.api.java.functions.KeySelector;
+import org.apache.flink.streaming.api.windowing.assigners.TumblingEventTimeWindows;
+import org.apache.flink.streaming.api.windowing.time.Time;
+ 
+...
+
+DataStream<Integer> orangeStream = ...
+DataStream<Integer> greenStream = ...
+
+orangeStream.join(greenStream)
+    .where(<KeySelector>)
+    .equalTo(<KeySelector>)
+    .window(TumblingEventTimeWindows.of(Time.seconds(2)))
+    .apply (new JoinFunction<Integer, Integer, String> (){
+        @Override
+        public String join(Integer first, Integer second) {
+            return first + "," + second;
+        }
+    });
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+
+{% highlight scala %}
+import org.apache.flink.streaming.api.windowing.assigners.SlidingEventTimeWindows;
+import org.apache.flink.streaming.api.windowing.time.Time;
+
+...
+
+val orangeStream: DataStream[Integer] = ...
+val greenStream: DataStream[Integer] = ...
+
+orangeStream.join(greenStream)
+    .where(elem => /* select key */)
+    .equalTo(elem => /* select key */)
+    .window(TumblingEventTimeWindows.of(Time.milliseconds(2)))
+    .apply { (e1, e2) => e1 + "," + e2 }
+{% endhighlight %}
+
+</div>
+</div>
+
+## Sliding Window Join
+When performing a sliding window join, all elements with a common key and common sliding
window are joined are pairwise combinations and passed on to the `JoinFunction` or `FlatJoinFunction`.
Elements of one stream that do not have elements from the other stream in the current sliding
window are not emitted! Note that some elements might be joined in one sliding window but
not in another!
+
+<img src="{{ site.baseurl }}/fig/sliding-window-join.svg" class="center" style="width:
80%;" />
+
+In this example we are using sliding windows with a size of two milliseconds and slide them
by one millisecond, resulting in the sliding windows `[-1, 0],[0,1],[1,2],[2,3], …`.<!--
TODO: Can -1 actually exist?--> The joined elements below the x-axis are the ones that
are passed to the `JoinFunction` for each sliding window. Here you can also see how for example
the orange ② is joined with the green ③ in the window `[2,3]`, but is not joined with
anything in the window `[1,2]`.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+
+{% highlight java %}
+import org.apache.flink.api.java.functions.KeySelector;
+import org.apache.flink.streaming.api.windowing.assigners.SlidingEventTimeWindows;
+import org.apache.flink.streaming.api.windowing.time.Time;
+
+...
+
+DataStream<Integer> orangeStream = ...
+DataStream<Integer> greenStream = ...
+
+orangeStream.join(greenStream)
+    .where(<KeySelector>)
+    .equalTo(<KeySelector>)
+    .window(SlidingEventTimeWindows.of(Time.milliseconds(2) /* size */, Time.milliseconds(1)
/* slide */))
+    .apply (new JoinFunction<Integer, Integer, String> (){
+        @Override
+        public String join(Integer first, Integer second) {
+            return first + "," + second;
+        }
+    });
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+
+{% highlight scala %}
+import org.apache.flink.streaming.api.windowing.assigners.SlidingEventTimeWindows;
+import org.apache.flink.streaming.api.windowing.time.Time;
+
+...
+
+val orangeStream: DataStream[Integer] = ...
+val greenStream: DataStream[Integer] = ...
+
+orangeStream.join(greenStream)
+    .where(elem => /* select key */)
+    .equalTo(elem => /* select key */)
+    .window(SlidingEventTimeWindows.of(Time.milliseconds(2) /* size */, Time.milliseconds(1)
/* slide */))
+    .apply { (e1, e2) => e1 + "," + e2 }
+{% endhighlight %}
+</div>
+</div>
+
+## Session Window Join
+When performing a session window join, all elements with the same key that when _"combined"_
fulfill the session criteria are joined in pairwise combinations and passed on to the `JoinFunction`
or `FlatJoinFunction`. Again this performs an inner join, so if there is a session window
that only contains elements from one stream, no output will be emitted!
+
+<img src="{{ site.baseurl }}/fig/session-window-join.svg" class="center" style="width:
80%;" />
+
+Here we define a session window join where each session is divided by a gap of at least 1ms.
There are three sessions, and in the first two sessions the joined elements from both streams
are passed to the `JoinFunction`. In the third session there are no elements in the green
stream, so ⑧ and ⑨ are not joined!
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+
+{% highlight java %}
+import org.apache.flink.api.java.functions.KeySelector;
+import org.apache.flink.streaming.api.windowing.assigners.EventTimeSessionWindows;
+import org.apache.flink.streaming.api.windowing.time.Time;
+ 
+...
+
+DataStream<Integer> orangeStream = ...
+DataStream<Integer> greenStream = ...
+
+orangeStream.join(greenStream)
+    .where(<KeySelector>)
+    .equalTo(<KeySelector>)
+    .window(EventTimeSessionWindows.withGap(Time.milliseconds(1)))
+    .apply (new JoinFunction<Integer, Integer, String> (){
+        @Override
+        public String join(Integer first, Integer second) {
+            return first + "," + second;
+        }
+    });
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+
+{% highlight scala %}
+import org.apache.flink.streaming.api.windowing.assigners.EventTimeSessionWindows;
+import org.apache.flink.streaming.api.windowing.time.Time;
+ 
+...
+
+val orangeStream: DataStream[Integer] = ...
+val greenStream: DataStream[Integer] = ...
+
+orangeStream.join(greenStream)
+    .where(elem => /* select key */)
+    .equalTo(elem => /* select key */)
+    .window(EventTimeSessionWindows.withGap(Time.milliseconds(1)))
+    .apply { (e1, e2) => e1 + "," + e2 }
+{% endhighlight %}
+
+</div>
+</div>
+
+# Interval Join
 
 Review comment:
   I'll have to think about a clever way to phrase this, because the lowerBound can be either
positive or negative depending on how you want your interval to look like. The only constraint
is that lowerBound <= upperBound must hold

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> Add separate docs page for different join types in DataStream API
> -----------------------------------------------------------------
>
>                 Key: FLINK-9877
>                 URL: https://issues.apache.org/jira/browse/FLINK-9877
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Documentation
>            Reporter: Florian Schmidt
>            Assignee: Florian Schmidt
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.6.0
>
>
> https://github.com/apache/flink/pull/6407



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