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https://issues.apache.org/jira/browse/FLINK-4062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15357243#comment-15357243
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ASF GitHub Bot commented on FLINK-4062:
---------------------------------------
Github user uce commented on a diff in the pull request:
https://github.com/apache/flink/pull/2154#discussion_r69151712
--- Diff: docs/apis/streaming/windows.md ---
@@ -24,1023 +24,608 @@ specific language governing permissions and
limitations
under the License.
-->
+Flink uses a concept called *windows* to divide a (potentially) infinite
`DataStream` into finite
+slices based on the timestamps of elements or other criteria. This
division is required when working
+with infinite streams of data and performing transformations that
aggregate elements.
+
+<span class="label label-info">Info</span> We will mostly talk about
*keyed windowing* here, i.e.
+windows that are applied on a `KeyedStream`. Keyed windows have the
advantage that elements are
+subdivided based on both window and key before being given to
+a user function. The work can thus be distributed across the cluster
+because the elements for different keys can be processed independently. If
you absolutely have to,
+you can check out [non-keyed windowing](#non-keyed-windowing) where we
describe how non-keyed
+windows work.
+
* This will be replaced by the TOC
{:toc}
-## Windows on Keyed Data Streams
-
-Flink offers a variety of methods for defining windows on a `KeyedStream`.
All of these group elements *per key*,
-i.e., each window will contain elements with the same key value.
+## Basics
-### Basic Window Constructs
+For a windowed transformations you must at least specify a *key*
+(see [specifying keys](apis/common/index.html#specifying-keys))
--- End diff --
link is broken
> Update Windowing Documentation
> ------------------------------
>
> Key: FLINK-4062
> URL: https://issues.apache.org/jira/browse/FLINK-4062
> Project: Flink
> Issue Type: Sub-task
> Components: Documentation
> Affects Versions: 1.1.0
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
>
> The window documentation could be a bit more principled and also needs
> updating with the new allowed lateness setting.
> There is also essentially no documentation about how to write a custom
> trigger.
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