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https://issues.apache.org/jira/browse/KAFKA-2856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15032294#comment-15032294
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ASF GitHub Bot commented on KAFKA-2856:
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Github user ymatsuda closed the pull request at:
https://github.com/apache/kafka/pull/604
> add KTable
> ----------
>
> Key: KAFKA-2856
> URL: https://issues.apache.org/jira/browse/KAFKA-2856
> Project: Kafka
> Issue Type: Sub-task
> Components: kafka streams
> Reporter: Yasuhiro Matsuda
>
> KTable is a special type of the stream that represents a changelog of a
> database table (or a key-value store).
> A changelog has to meet the following requirements.
> * Key-value mapping is surjective in the database table (the key must be the
> primary key).
> * All insert/update/delete events are delivered in order for the same key
> * An update event has the whole data (not just delta).
> * A delete event is represented by the null value.
> KTable does not necessarily materialized as a local store. It may be
> materialized when necessary. (see below)
> KTable supports look-up by key. KTable is materialized implicitly when
> look-up is necessary.
> * KTable may be created from a topic. (Base KTable)
> * KTable may be created from another KTable by filter(), filterOut(),
> mapValues(). (Derived KTable)
> * A call to the user supplied function is skipped when the value is null
> since such an event represents a deletion.
> * Instead of dropping, events filtered out by filter() or filterOut() are
> converted to delete events. (Can we avoid this?)
> * map(), flatMap() and flatMapValues() are not supported since they may
> violate the changelog requirements
> A derived KTable may be persisted to a topic by to() or through(). through()
> creates another base KTable.
> KTable can be converted to KStream by the toStream() method.
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