Yasuhiro Matsuda created KAFKA-2856:
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Summary: 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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