MINOR: update Kafka Streams docs with 3.3 KIP information (#16316)

Reviewers: Lucas Brutschy <lbrutschy@confluent.io>, Jim Galasyn <jim.galasyn@confluent.io>

docs/ops.html

@@ -2863,10 +2863,11 @@ active-process-ratio metrics which have a recording level of <code>info</code>:
 
  <h5 class="anchor-heading"><a id="kafka_streams_node_monitoring" class="anchor-link"></a><a href="#kafka_streams_node_monitoring">Processor Node Metrics</a></h5>
  The following metrics are only available on certain types of nodes, i.e., the process-* metrics are only available for
- source processor nodes, the suppression-emit-* metrics are only available for suppression operation nodes, and the
- record-e2e-latency-* metrics are only available for source processor nodes and terminal nodes (nodes without successor
+ source processor nodes, the <code>suppression-emit-*</code> metrics are only available for suppression operation nodes,
+ <code>emit-final-*</code> metrics are only available for windowed aggregations nodes, and the
+ <code>record-e2e-latency-*</code> metrics are only available for source processor nodes and terminal nodes (nodes without successor
  nodes).
- All of the metrics have a recording level of <code>debug</code>, except for the record-e2e-latency-* metrics which have
+ All of the metrics have a recording level of <code>debug</code>, except for the <code>record-e2e-latency-*</code> metrics which have
  a recording level of <code>info</code>:
  <table class="data-table">
       <tbody>
@@ -2905,6 +2906,26 @@ active-process-ratio metrics which have a recording level of <code>info</code>:
         <td>The total number of records that have been emitted downstream from suppression operation nodes.</td>
         <td>kafka.streams:type=stream-processor-node-metrics,thread-id=([-.\w]+),task-id=([-.\w]+),processor-node-id=([-.\w]+)</td>
       </tr>
+      <tr>
+        <td>emit-final-latency-max</td>
+        <td>The max latency to emit final records when a record could be emitted.</td>
+        <td>kafka.streams:type=stream-processor-node-metrics,thread-id=([-.\w]+),task-id=([-.\w]+),processor-node-id=([-.\w]+)</td>
+      </tr>
+      <tr>
+        <td>emit-final-latency-avg</td>
+        <td>The avg latency to emit final records when a record could be emitted.</td>
+        <td>kafka.streams:type=stream-processor-node-metrics,thread-id=([-.\w]+),task-id=([-.\w]+),processor-node-id=([-.\w]+)</td>
+      </tr>
+      <tr>
+        <td>emit-final-records-rate</td>
+        <td>The rate of records emitted when records could be emitted.</td>
+        <td>kafka.streams:type=stream-processor-node-metrics,thread-id=([-.\w]+),task-id=([-.\w]+),processor-node-id=([-.\w]+)</td>
+      </tr>
+      <tr>
+        <td>emit-final-records-total</td>
+        <td>The total number of records emitted.</td>
+        <td>kafka.streams:type=stream-processor-node-metrics,thread-id=([-.\w]+),task-id=([-.\w]+),processor-node-id=([-.\w]+)</td>
+      </tr>
       <tr>
         <td>record-e2e-latency-avg</td>
         <td>The average end-to-end latency of a record, measured by comparing the record timestamp with the system time when it has been fully processed by the node.</td>

docs/streams/upgrade-guide.html

@@ -105,6 +105,62 @@
         More details about the new config <code>StreamsConfig#TOPOLOGY_OPTIMIZATION</code> can be found in <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-295%3A+Add+Streams+Configuration+Allowing+for+Optional+Topology+Optimization">KIP-295</a>.
     </p>
 
+    <h3><a id="streams_api_changes_330" href="#streams_api_changes_330">Streams API changes in 3.3.0</a></h3>
+    <p>
+      Kafka Streams does not send a "leave group" request when an instance is closed. This behavior implies
+      that a rebalance is delayed until <code>max.poll.interval.ms</code> passed.
+      <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-812%3A+Introduce+another+form+of+the+%60KafkaStreams.close%28%29%60+API+that+forces+the+member+to+leave+the+consumer+group">KIP-812</a>
+      introduces <code>KafkaStreams.close(CloseOptions)</code> overload, which allows forcing an instance to leave the
+      group immediately.
+
+      Note: Due to internal limitations, <code>CloseOptions</code> only works for static consumer groups at this point
+      (cf. <a href="https://issues.apache.org/jira/browse/KAFKA-16514">KAFKA-16514</a> for more details and a fix in
+      some future release).
+    </p>
+
+    <p>
+      <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-820%3A+Extend+KStream+process+with+new+Processor+API">KIP-820</a>
+      adapts the PAPI type-safety improvement of KIP-478 into the DSL. The existing methods <code>KStream.transform</code>,
+      <code>KStream.flatTransform</code>, <code>KStream.transformValues</code>, and <code>KStream.flatTransformValues</code>
+      as well as all overloads of <code>void KStream.process</code> are deprecated in favor of the newly added methods
+      <ul>
+        <li><code>KStream&lt;KOut,VOut&gt; KStream.process(ProcessorSupplier, ...)</code></li>
+        <li><code>KStream&lt;K,VOut&gt; KStream.processValues(FixedKeyProcessorSupplier, ...)</code></li>
+      </ul>
+      Both new methods have multiple overloads and return a <code>KStream</code> instead of <code>void</code> as the
+      deprecated <code>process()</code> methods did. In addition, <code>FixedKeyProcessor</code>, <code>FixedKeyRecord</code>,
+      <code>FixedKeyProcessorContext</code>, and <code>ContextualFixedKeyProcessor</code> are introduced to guard against
+      disallowed key modification inside <code>processValues()</code>. Furthermore, <code>ProcessingContext</code> is
+      added for a better interface hierarchy.
+    </p>
+
+    <p>
+      Emitting a windowed aggregation result only after a window is closed is currently supported via the
+      <code>suppress()</code> operator. However, <code>suppress()</code> uses an in-memory implementation and does not
+      support RocksDB. To close this gap,
+      <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-825%3A+introduce+a+new+API+to+control+when+aggregated+results+are+produced">KIP-825</a>
+      introduces "emit strategies", which are built into the aggregation operator directly to use the already existing
+      RocksDB store. <code>TimeWindowedKStream.emitStrategy(EmitStrategy)</code> and
+      <code>SessionWindowedKStream.emitStrategy(EmitStrategy)</code> allow picking between "emit on window update" (default)
+      and "emit on window close" strategies. Additionally, a few new emit metrics are added, as well as a necessary
+      new method, <code>SessionStore.findSessions(long, long)</code>.
+    </p>
+
+    <p>
+      <a href="https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=211882832">KIP-834</a> allows pausing
+      and resuming a Kafka Streams instance. Pausing implies that processing input records and executing punctuations will
+      be skipped; Kafka Streams will continue to poll to maintain its group membership and may commit offsets.
+      In addition to the new methods <code>KafkaStreams.pause()</code> and <code>KafkaStreams.resume()</code>, it is also
+      supported to check if an instance is paused via the <code>KafkaStreams.isPaused()</code> method.
+    </p>
+
+    <p>
+      To improve monitoring of Kafka Streams applications, <a href="https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=211886093">KIP-846</a>
+      adds four new metrics <code>bytes-consumed-total</code>, <code>records-consumed-total</code>,
+      <code>bytes-produced-total</code>, and <code>records-produced-total</code> within a new <b>topic level</b> scope.
+      The metrics are collected at INFO level for source and sink nodes, respectively.
+    </p>
+
     <h3><a id="streams_api_changes_320" href="#streams_api_changes_320">Streams API changes in 3.2.0</a></h3>
     <p>
         RocksDB offers many metrics which are critical to monitor and tune its performance. Kafka Streams started to make RocksDB metrics accessible