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https://issues.apache.org/jira/browse/BEAM-8045?focusedWorklogId=315791&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-315791
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ASF GitHub Bot logged work on BEAM-8045:
----------------------------------------
Author: ASF GitHub Bot
Created on: 20/Sep/19 16:55
Start Date: 20/Sep/19 16:55
Worklog Time Spent: 10m
Work Description: aaltay commented on pull request #9406: [BEAM-8045]
Custom windows patterns
URL: https://github.com/apache/beam/pull/9406#discussion_r326717581
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File path: website/src/documentation/patterns/custom-windows.md
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@@ -0,0 +1,112 @@
+---
+layout: section
+title: "Custom window patterns"
+section_menu: section-menu/documentation.html
+permalink: /documentation/patterns/custom-windows/
+---
+<!--
+Licensed 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.
+-->
+
+# Custom window patterns
+The samples on this page demonstrate common custom window patterns. You can
create custom windows with [`WindowFn` functions]({{ site.baseurl
}}/documentation/programming-guide/#provided-windowing-functions). For more
information, see the [programming guide section on windowing]({{ site.baseurl
}}/documentation/programming-guide/#windowing).
+
+**Note**: Custom merging windows isn't supported in Python.
+
+## Using data to dynamically set session window gaps
+
+You can modify the
[`assignWindows`](https://beam.apache.org/releases/javadoc/current/index.html?org/apache/beam/sdk/transforms/windowing/SlidingWindows.html)
function to use data-driven gaps instead of fixed windows.
+
+Access the `assignWindows` function through
`WindowFn.AssignContext.element()`. The original, fixed-duration
`assignWindows` function is:
+
+```java
+{% github_sample
/apache/beam/blob/master/examples/java/src/main/java/org/apache/beam/examples/snippets/Snippets.java
tag:CustomSessionWindow1
+%}
+```
+
+### Creating data-driven gaps
+To use data-driven gaps, add the following snippets to the `assignWindows`
function:
+- A default value for when the custom gap is not present in the data
+- A way to set the attribute from the main pipeline as a method of the custom
windows
+
+For example, the following function assigns each element to a window between
the timestamp and `gapDuration`:
+
+```java
+{% github_sample
/apache/beam/blob/master/examples/java/src/main/java/org/apache/beam/examples/snippets/Snippets.java
tag:CustomSessionWindow3
+%}
+```
+
+In this function, the `withDefaultGapDuration` and `withGapAttribute` methods
are:
+
+```java
+{% github_sample
/apache/beam/blob/master/examples/java/src/main/java/org/apache/beam/examples/snippets/Snippets.java
tag:CustomSessionWindow4
+%}
+```
+
+Then, the new `gapAttribute` field and constructor dynamically create session
windows with the calculated gap duration:
+
+```java
+{% github_sample
/apache/beam/blob/master/examples/java/src/main/java/org/apache/beam/examples/snippets/Snippets.java
tag:CustomSessionWindow2
+%}
+```
+
+### Windowing messages into sessions
+After creating data-driven gaps, you can window Pub/Sub messages into the new,
custom sessions:
Review comment:
How do we convert from pub/sub to tablerows? Should we mention that a
conversion needs to happen. Or maybe not mention pubsub at all.
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Issue Time Tracking
-------------------
Worklog Id: (was: 315791)
Time Spent: 1.5h (was: 1h 20m)
> Publish custom windows pattern
> ------------------------------
>
> Key: BEAM-8045
> URL: https://issues.apache.org/jira/browse/BEAM-8045
> Project: Beam
> Issue Type: Improvement
> Components: website
> Reporter: Cyrus Maden
> Assignee: Cyrus Maden
> Priority: Minor
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
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