KAFKA-8942: Document RocksDB metrics

Author: Bruno Cadonna <bruno@confluent.io>

Reviewers: Guozhang Wang <wangguoz@gmail.com>

Closes #7490 from cadonna/AK8942-docs-rocksdb_metrics

Minor comments

docs/ops.html

@@ -1979,6 +1979,108 @@ All the following metrics have a recording level of <code>debug</code>:
     </tbody>
  </table>
 
+  <h5><a id="kafka_streams_rocksdb_monitoring" href="#kafka_streams_rocksdb_monitoring">RocksDB Metrics</a></h5>
+  All the following metrics have a recording level of <code>debug</code>.
+  The metrics are collected every minute from the RocksDB state stores.
+  If a state store consists of multiple RocksDB instances as it is the case for aggregations over time and session windows,
+  each metric reports an aggregation over the RocksDB instances of the state store.
+  Note that the <code>store-scope</code> for built-in RocksDB state stores are currently the following:
+  <ul>
+    <li><code>rocksdb-state</code> (for RocksDB backed key-value store)</li>
+    <li><code>rocksdb-window-state</code> (for RocksDB backed window store)</li>
+    <li><code>rocksdb-session-state</code> (for RocksDB backed session store)</li>
+  </ul>
+
+  <table class="data-table">
+    <tbody>
+    <tr>
+      <th>Metric/Attribute name</th>
+      <th>Description</th>
+      <th>Mbean name</th>
+    </tr>
+    <tr>
+      <td>bytes-written-rate</td>
+      <td>The average number of bytes written per second to the RocksDB state store.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>bytes-written-total</td>
+      <td>The total number of bytes written to the RocksDB state store.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>bytes-read-rate</td>
+      <td>The average number of bytes read per second from the RocksDB state store.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>bytes-read-total</td>
+      <td>The total number of bytes read from the RocksDB state store.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>memtable-bytes-flushed-rate</td>
+      <td>The average number of bytes flushed per second from the memtable to disk.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>memtable-bytes-flushed-total</td>
+      <td>The total number of bytes flushed from the memtable to disk.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>memtable-hit-ratio</td>
+      <td>The ratio of memtable hits relative to all lookups to the memtable.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>block-cache-data-hit-ratio</td>
+      <td>The ratio of block cache hits for data blocks relative to all lookups for data blocks to the block cache.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>block-cache-index-hit-ratio</td>
+      <td>The ratio of block cache hits for index blocks relative to all lookups for index blocks to the block cache.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>block-cache-filter-hit-ratio</td>
+      <td>The ratio of block cache hits for filter blocks relative to all lookups for filter blocks to the block cache.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>write-stall-duration-avg</td>
+      <td>The average duration of write stalls in ms.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>write-stall-duration-total</td>
+      <td>The total duration of write stalls in ms.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>bytes-read-compaction-rate</td>
+      <td>The average number of bytes read per second during compaction.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>bytes-written-compaction-rate</td>
+      <td>The average number of bytes written per second during compaction.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>number-open-files</td>
+      <td>The number of current open files.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    <tr>
+      <td>number-file-errors-total</td>
+      <td>The total number of file errors occurred.</td>
+      <td>kafka.streams:type=stream-state-metrics,client-id=([-.\w]+),task-id=([-.\w]+),[store-scope]-id=([-.\w]+)</td>
+    </tr>
+    </tbody>
+  </table>
+
   <h5><a id="kafka_streams_cache_monitoring" href="#kafka_streams_cache_monitoring">Record Cache Metrics</a></h5>
   All the following metrics have a recording level of <code>debug</code>: