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<h1 id="kafka-lookups">Kafka Lookups</h1>
<div class="note caution">
Lookups are an <a href="../experimental.html">experimental</a> feature.
</div>
<p>To use this Apache Druid (incubating) extension, make sure to <a href="../../operations/including-extensions.html">include</a> <code>druid-lookups-cached-global</code> and <code>druid-kafka-extraction-namespace</code> as an extension.</p>
<p>If you need updates to populate as promptly as possible, it is possible to plug into a kafka topic whose key is the old value and message is the desired new value (both in UTF-8) as a LookupExtractorFactory.</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;kafka&quot;</span><span class="p">,</span>
<span class="nt">&quot;kafkaTopic&quot;</span><span class="p">:</span><span class="s2">&quot;testTopic&quot;</span><span class="p">,</span>
<span class="nt">&quot;kafkaProperties&quot;</span><span class="p">:{</span><span class="nt">&quot;zookeeper.connect&quot;</span><span class="p">:</span><span class="s2">&quot;somehost:2181/kafka&quot;</span><span class="p">}</span>
<span class="p">}</span>
</code></pre></div>
<table><thead>
<tr>
<th>Parameter</th>
<th>Description</th>
<th>Required</th>
<th>Default</th>
</tr>
</thead><tbody>
<tr>
<td><code>kafkaTopic</code></td>
<td>The kafka topic to read the data from</td>
<td>Yes</td>
<td></td>
</tr>
<tr>
<td><code>kafkaProperties</code></td>
<td>Kafka consumer properties. At least&quot;zookeeper.connect&quot; must be specified. Only the zookeeper connector is supported</td>
<td>Yes</td>
<td></td>
</tr>
<tr>
<td><code>connectTimeout</code></td>
<td>How long to wait for an initial connection</td>
<td>No</td>
<td><code>0</code> (do not wait)</td>
</tr>
<tr>
<td><code>isOneToOne</code></td>
<td>The map is a one-to-one (see <a href="../../querying/dimensionspecs.html">Lookup DimensionSpecs</a>)</td>
<td>No</td>
<td><code>false</code></td>
</tr>
</tbody></table>
<p>The extension <code>kafka-extraction-namespace</code> enables reading from a kafka feed which has name/key pairs to allow renaming of dimension values. An example use case would be to rename an ID to a human readable format.</p>
<p>The consumer properties <code>group.id</code> and <code>auto.offset.reset</code> CANNOT be set in <code>kafkaProperties</code> as they are set by the extension as <code>UUID.randomUUID().toString()</code> and <code>smallest</code> respectively.</p>
<p>See <a href="../../querying/lookups.html">lookups</a> for how to configure and use lookups.</p>
<h1 id="limitations">Limitations</h1>
<p>Currently the Kafka lookup extractor feeds the entire kafka stream into a local cache. If you are using OnHeap caching, this can easily clobber your java heap if the kafka stream spews a lot of unique keys.
OffHeap caching should alleviate these concerns, but there is still a limit to the quantity of data that can be stored.
There is currently no eviction policy.</p>
<h2 id="testing-the-kafka-rename-functionality">Testing the Kafka rename functionality</h2>
<p>To test this setup, you can send key/value pairs to a kafka stream via the following producer console:</p>
<div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>./bin/kafka-console-producer.sh --property parse.key=true --property key.separator=&quot;-&gt;&quot; --broker-list localhost:9092 --topic testTopic
</code></pre></div>
<p>Renames can then be published as <code>OLD_VAL-&gt;NEW_VAL</code> followed by newline (enter or return)</p>
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