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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9637) Add public user documentation for TTL feature
Date Sun, 29 Jul 2018 23:15:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16561294#comment-16561294

ASF GitHub Bot commented on FLINK-9637:

eliaslevy commented on a change in pull request #6379: [FLINK-9637] Add public user documentation
for state TTL feature
URL: https://github.com/apache/flink/pull/6379#discussion_r205990823

 File path: docs/dev/stream/state/state.md
 @@ -266,6 +266,92 @@ a `ValueState`. Once the count reaches 2 it will emit the average and
clear the
 we start over from `0`. Note that this would keep a different state value for each different
 key if we had tuples with different values in the first field.
+### State time-to-live (TTL)
+A time-to-live (TTL) can be assigned to the keyed state value. 
+In this case it will expire after the configured TTL
+and its stored value will be cleaned up based on the best effort.
+Depending on configuration, the expired state can become unavailable for read access
+even if it is not cleaned up yet. In this case it behaves as if it does not exist any more.
+The collection types of state support TTL on entry level: 
+separate list elements and map entries expire independently. 
+The behaviour of state with TTL firstly should be configured by building `StateTtlConfiguration`:
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+StateTtlConfiguration ttlConfig = StateTtlConfiguration
+    .newBuilder(Time.seconds(1))
+    .setTtlUpdateType(StateTtlConfiguration.TtlUpdateType.OnCreateAndWrite)
+    .setStateVisibility(StateTtlConfiguration.TtlStateVisibility.NeverReturnExpired)
+    .build();
+{% endhighlight %}
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+val ttlConfig = StateTtlConfiguration
+    .newBuilder(Time.seconds(1))
+    .setTtlUpdateType(StateTtlConfiguration.TtlUpdateType.OnCreateAndWrite)
+    .setStateVisibility(StateTtlConfiguration.TtlStateVisibility.NeverReturnExpired)
+    .build()
+{% endhighlight %}
+It has several options to consider. 
+The first parameter of `newBuilder` method is mandatory, it is a value of time-to-live itself.
+The update type configures when the time-to-live of state value is prolonged (default `OnCreateAndWrite`):
+ - `StateTtlConfiguration.TtlUpdateType.OnCreateAndWrite` - only on creation and write access,
+ - `StateTtlConfiguration.TtlUpdateType.OnReadAndWrite` - also on read access.
+The state visibility configures whether the expired value is returned on read access 
+if it is not cleaned up yet (default `NeverReturnExpired`):
+ - `StateTtlConfiguration.TtlStateVisibility.NeverReturnExpired` - expired value is never
+ - `StateTtlConfiguration.TtlStateVisibility.ReturnExpiredIfNotCleanedUp` - returned if still
+The TTL can be enabled in descriptor for any type of state:
 Review comment:
   TTL functionality can be enabled in the descriptor of any type of state:

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> Add public user documentation for TTL feature
> ---------------------------------------------
>                 Key: FLINK-9637
>                 URL: https://issues.apache.org/jira/browse/FLINK-9637
>             Project: Flink
>          Issue Type: Sub-task
>          Components: State Backends, Checkpointing
>    Affects Versions: 1.6.0
>            Reporter: Andrey Zagrebin
>            Assignee: Andrey Zagrebin
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.6.0

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