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[KAFKA-10722] doc: Described the types of the stores used #9607

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mjsax merged 2 commits into from
Dec 1, 2020
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[KAFKA-10722] doc: Described the types of the stores used #9607

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doc: Described the types of the stores used
fml2 Nov 17, 2020
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docs: Improved wording
fml2 Nov 18, 2020
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6 changes: 6 additions & 0 deletions docs/streams/developer-guide/dsl-api.html
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Expand Up @@ -870,6 +870,12 @@ <h4 class="anchor-heading"><a id="streams_concepts_globalktable" class="anchor-l
<p id="streams-developer-guide-dsl-transformations-stateful-overview">Stateful transformations depend on state for processing inputs and producing outputs and require a <a class="reference internal" href="../architecture.html#streams_architecture_state"><span class="std std-ref">state store</span></a> associated with the stream processor. For example, in aggregating operations, a windowing state store is used to collect the latest aggregation results per
window. In join operations, a windowing state store is used to collect all of the records received so far within the
defined window boundary.</p>
<p><b>Note:</b> Following store types are used regardless of the possibly specified type (via the parameter <code class="docutils literal"><span class="pre">materialized</span></code>):
<ul class="simple">
<li>non-windowed aggregations and non-windowed KTables use <a class="reference external" href="/{{version}}/javadoc/org/apache/kafka/streams/state/TimestampedKeyValueStore.html">TimestampedKeyValueStore</a>s</li>
<li>time-windowed aggregations and KStream-KStream joins use <a class="reference external" href="/{{version}}/javadoc/org/apache/kafka/streams/state/TimestampedWindowStore.html">TimestampedWindowStore</a>s</li>
<li>session windowed aggregations use <a class="reference external" href="/{{version}}/javadoc/org/apache/kafka/streams/state/SessionStore.html">SessionStore</a>s (there is no timestamped session store as of now)</li>
</ul>
<p>Note, that state stores are fault-tolerant.
In case of failure, Kafka Streams guarantees to fully restore all state stores prior to resuming the processing.
See <a class="reference internal" href="../architecture.html#streams_architecture_recovery"><span class="std std-ref">Fault Tolerance</span></a> for further information.</p>
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