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<p>Druid uses a module system that allows for the addition of extensions at runtime.</p>
<h2><a class="anchor" aria-hidden="true" id="writing-your-own-extensions"></a><a href="#writing-your-own-extensions" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Writing your own extensions</h2>
<p>Druid's extensions leverage Guice in order to add things at runtime. Basically, Guice is a framework for Dependency Injection, but we use it to hold the expected object graph of the Druid process. Extensions can make any changes they want/need to the object graph via adding Guice bindings. While the extensions actually give you the capability to change almost anything however you want, in general, we expect people to want to extend one of the things listed below. This means that we honor our <a href="/docs/latest/development/versioning.html">versioning strategy</a> for changes that affect the interfaces called out on this page, but other interfaces are deemed &quot;internal&quot; and can be changed in an incompatible manner even between patch releases.</p>
<ol>
<li>Add a new deep storage implementation by extending the <code>org.apache.druid.segment.loading.DataSegment*</code> and
<code>org.apache.druid.tasklogs.TaskLog*</code> classes.</li>
<li>Add a new Firehose by extending <code>org.apache.druid.data.input.FirehoseFactory</code>.</li>
<li>Add a new input parser by extending <code>org.apache.druid.data.input.impl.InputRowParser</code>.</li>
<li>Add a new string-based input format by extending <code>org.apache.druid.data.input.impl.ParseSpec</code>.</li>
<li>Add Aggregators by extending <code>org.apache.druid.query.aggregation.AggregatorFactory</code>, <code>org.apache.druid.query.aggregation.Aggregator</code>,
and <code>org.apache.druid.query.aggregation.BufferAggregator</code>.</li>
<li>Add PostAggregators by extending <code>org.apache.druid.query.aggregation.PostAggregator</code>.</li>
<li>Add ExtractionFns by extending <code>org.apache.druid.query.extraction.ExtractionFn</code>.</li>
<li>Add Complex metrics by extending <code>org.apache.druid.segment.serde.ComplexMetricSerde</code>.</li>
<li>Add new Query types by extending <code>org.apache.druid.query.QueryRunnerFactory</code>, <code>org.apache.druid.query.QueryToolChest</code>, and
<code>org.apache.druid.query.Query</code>.</li>
<li>Add new Jersey resources by calling <code>Jerseys.addResource(binder, clazz)</code>.</li>
<li>Add new Jetty filters by extending <code>org.apache.druid.server.initialization.jetty.ServletFilterHolder</code>.</li>
<li>Add new secret providers by extending <code>org.apache.druid.metadata.PasswordProvider</code>.</li>
<li>Bundle your extension with all the other Druid extensions</li>
</ol>
<p>Extensions are added to the system via an implementation of <code>org.apache.druid.initialization.DruidModule</code>.</p>
<h3><a class="anchor" aria-hidden="true" id="creating-a-druid-module"></a><a href="#creating-a-druid-module" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Creating a Druid Module</h3>
<p>The DruidModule class is has two methods</p>
<ol>
<li>A <code>configure(Binder)</code> method</li>
<li>A <code>getJacksonModules()</code> method</li>
</ol>
<p>The <code>configure(Binder)</code> method is the same method that a normal Guice module would have.</p>
<p>The <code>getJacksonModules()</code> method provides a list of Jackson modules that are used to help initialize the Jackson ObjectMapper instances used by Druid. This is how you add extensions that are instantiated via Jackson (like AggregatorFactory and Firehose objects) to Druid.</p>
<h3><a class="anchor" aria-hidden="true" id="registering-your-druid-module"></a><a href="#registering-your-druid-module" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Registering your Druid Module</h3>
<p>Once you have your DruidModule created, you will need to package an extra file in the <code>META-INF/services</code> directory of your jar. This is easiest to accomplish with a maven project by creating files in the <code>src/main/resources</code> directory. There are examples of this in the Druid code under the <code>cassandra-storage</code>, <code>hdfs-storage</code> and <code>s3-extensions</code> modules, for examples.</p>
<p>The file that should exist in your jar is</p>
<p><code>META-INF/services/org.apache.druid.initialization.DruidModule</code></p>
<p>It should be a text file with a new-line delimited list of package-qualified classes that implement DruidModule like</p>
<pre><code class="hljs">org<span class="hljs-selector-class">.apache</span><span class="hljs-selector-class">.druid</span><span class="hljs-selector-class">.storage</span><span class="hljs-selector-class">.cassandra</span><span class="hljs-selector-class">.CassandraDruidModule</span>
</code></pre>
<p>If your jar has this file, then when it is added to the classpath or as an extension, Druid will notice the file and will instantiate instances of the Module. Your Module should have a default constructor, but if you need access to runtime configuration properties, it can have a method with @Inject on it to get a Properties object injected into it from Guice.</p>
<h3><a class="anchor" aria-hidden="true" id="adding-a-new-deep-storage-implementation"></a><a href="#adding-a-new-deep-storage-implementation" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding a new deep storage implementation</h3>
<p>Check the <code>azure-storage</code>, <code>google-storage</code>, <code>cassandra-storage</code>, <code>hdfs-storage</code> and <code>s3-extensions</code> modules for examples of how to do this.</p>
<p>The basic idea behind the extension is that you need to add bindings for your DataSegmentPusher and DataSegmentPuller objects. The way to add them is something like (taken from HdfsStorageDruidModule)</p>
<pre><code class="hljs css language-java">Binders.dataSegmentPullerBinder(binder)
.addBinding(<span class="hljs-string">"hdfs"</span>)
.to(HdfsDataSegmentPuller.class).in(LazySingleton.class);
Binders.dataSegmentPusherBinder(binder)
.addBinding(<span class="hljs-string">"hdfs"</span>)
.to(HdfsDataSegmentPusher.class).in(LazySingleton.class);
</code></pre>
<p><code>Binders.dataSegment*Binder()</code> is a call provided by the druid-core jar which sets up a Guice multibind &quot;MapBinder&quot;. If that doesn't make sense, don't worry about it, just think of it as a magical incantation.</p>
<p><code>addBinding(&quot;hdfs&quot;)</code> for the Puller binder creates a new handler for loadSpec objects of type &quot;hdfs&quot;. For the Pusher binder it creates a new type value that you can specify for the <code>druid.storage.type</code> parameter.</p>
<p><code>to(...).in(...);</code> is normal Guice stuff.</p>
<p>In addition to DataSegmentPusher and DataSegmentPuller, you can also bind:</p>
<ul>
<li>DataSegmentKiller: Removes segments, used as part of the Kill Task to delete unused segments, i.e. perform garbage collection of segments that are either superseded by newer versions or that have been dropped from the cluster.</li>
<li>DataSegmentMover: Allow migrating segments from one place to another, currently this is only used as part of the MoveTask to move unused segments to a different S3 bucket or prefix, typically to reduce storage costs of unused data (e.g. move to glacier or cheaper storage)</li>
<li>DataSegmentArchiver: Just a wrapper around Mover, but comes with a pre-configured target bucket/path, so it doesn't have to be specified at runtime as part of the ArchiveTask.</li>
</ul>
<h3><a class="anchor" aria-hidden="true" id="validating-your-deep-storage-implementation"></a><a href="#validating-your-deep-storage-implementation" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Validating your deep storage implementation</h3>
<p><strong>WARNING!</strong> This is not a formal procedure, but a collection of hints to validate if your new deep storage implementation is able do push, pull and kill segments.</p>
<p>It's recommended to use batch ingestion tasks to validate your implementation.
The segment will be automatically rolled up to Historical note after ~20 seconds.
In this way, you can validate both push (at realtime process) and pull (at Historical process) segments.</p>
<ul>
<li>DataSegmentPusher</li>
</ul>
<p>Wherever your data storage (cloud storage service, distributed file system, etc.) is, you should be able to see one new file: <code>index.zip</code> (<code>partitionNum_index.zip</code> for HDFS data storage) after your ingestion task ends.</p>
<ul>
<li>DataSegmentPuller</li>
</ul>
<p>After ~20 secs your ingestion task ends, you should be able to see your Historical process trying to load the new segment.</p>
<p>The following example was retrieved from a Historical process configured to use Azure for deep storage:</p>
<pre><code class="hljs">2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:42:33,450 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.server.coordination.ZkCoordinator - New request[LOAD: dde_2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00
.000Z_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z] with zNode[/druid/dev/loadQueue/192.168.33.104:8081/dde_2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.000Z_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.
484Z].
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:42:33,451 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.server.coordination.ZkCoordinator - Loading segment dde_2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.0
00Z_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:42:33,463 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.guice.JsonConfigurator - Loaded class[class org.apache.druid.storage.azure.AzureAccountConfig] from props[drui
d.azure.] as [org.apache.druid.storage.azure.AzureAccountConfig@759c9ad9]
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:49:08,275 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.utils.CompressionUtils - Unzipping file[/opt/druid/tmp/compressionUtilZipCache1263964429587449785.z
ip] to [/opt/druid/zk_druid/dde/2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.000Z/2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z/0]
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:49:08,276 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.storage.azure.AzureDataSegmentPuller - Loaded 1196 bytes from [dde/2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>
T00:00:00.000Z/2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z/0/index.zip] to [/opt/druid/zk_druid/dde/2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.000Z/2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z/0]
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:49:08,277 WARN [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.segment.loading.SegmentLoaderLocalCacheManager - Segment [dde_2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.000Z_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z] is different than expected size. Expected [0] found [1196]
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:49:08,282 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.server.coordination.BatchDataSegmentAnnouncer - Announcing segment[dde_2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.000Z_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z] at path[/druid/dev/segments/192.168.33.104:8081/192.168.33.104:8081_historical__default_tier_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:49:08.282Z_7bb87230ebf940188511dd4a53ffd7351]
2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:49:08,292 INFO [ZkCoordinator<span class="hljs-string">-0</span>] org.apache.druid.server.coordination.ZkCoordinator - Completed request [LOAD: dde_2015<span class="hljs-string">-01</span><span class="hljs-string">-02</span>T00:00:00.000Z_2015<span class="hljs-string">-01</span><span class="hljs-string">-03</span>T00:00:00.000Z_2015<span class="hljs-string">-04</span><span class="hljs-string">-14</span>T02:41:09.484Z]
</code></pre>
<ul>
<li>DataSegmentKiller</li>
</ul>
<p>The easiest way of testing the segment killing is marking a segment as not used and then starting a killing task through the old Coordinator console.</p>
<p>To mark a segment as not used, you need to connect to your metadata storage and update the <code>used</code> column to <code>false</code> on the segment table rows.</p>
<p>To start a segment killing task, you need to access the old Coordinator console <code>http://&lt;COODRINATOR_IP&gt;:&lt;COORDINATOR_PORT/old-console/kill.html</code> then select the appropriate datasource and then input a time range (e.g. <code>2000/3000</code>).</p>
<p>After the killing task ends, <code>index.zip</code> (<code>partitionNum_index.zip</code> for HDFS data storage) file should be deleted from the data storage.</p>
<h3><a class="anchor" aria-hidden="true" id="adding-a-new-firehose"></a><a href="#adding-a-new-firehose" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding a new Firehose</h3>
<p>There is an example of this in the <code>s3-extensions</code> module with the StaticS3FirehoseFactory.</p>
<p>Adding a Firehose is done almost entirely through the Jackson Modules instead of Guice. Specifically, note the implementation</p>
<pre><code class="hljs css language-java"><span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> List&lt;? extends Module&gt; getJacksonModules()
{
<span class="hljs-keyword">return</span> ImmutableList.of(
<span class="hljs-keyword">new</span> SimpleModule().registerSubtypes(<span class="hljs-keyword">new</span> NamedType(StaticS3FirehoseFactory.class, <span class="hljs-string">"static-s3"</span>))
);
}
</code></pre>
<p>This is registering the FirehoseFactory with Jackson's polymorphic serialization/deserialization layer. More concretely, having this will mean that if you specify a <code>&quot;firehose&quot;: { &quot;type&quot;: &quot;static-s3&quot;, ... }</code> in your realtime config, then the system will load this FirehoseFactory for your firehose.</p>
<p>Note that inside of Druid, we have made the @JacksonInject annotation for Jackson deserialized objects actually use the base Guice injector to resolve the object to be injected. So, if your FirehoseFactory needs access to some object, you can add a @JacksonInject annotation on a setter and it will get set on instantiation.</p>
<h3><a class="anchor" aria-hidden="true" id="adding-aggregators"></a><a href="#adding-aggregators" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding Aggregators</h3>
<p>Adding AggregatorFactory objects is very similar to Firehose objects. They operate purely through Jackson and thus should just be additions to the Jackson modules returned by your DruidModule.</p>
<h3><a class="anchor" aria-hidden="true" id="adding-complex-metrics"></a><a href="#adding-complex-metrics" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding Complex Metrics</h3>
<p>Adding ComplexMetrics is a little ugly in the current version. The method of getting at complex metrics is through registration with the <code>ComplexMetrics.registerSerde()</code> method. There is no special Guice stuff to get this working, just in your <code>configure(Binder)</code> method register the serialization/deserialization.</p>
<h3><a class="anchor" aria-hidden="true" id="adding-new-query-types"></a><a href="#adding-new-query-types" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding new Query types</h3>
<p>Adding a new Query type requires the implementation of three interfaces.</p>
<ol>
<li><code>org.apache.druid.query.Query</code></li>
<li><code>org.apache.druid.query.QueryToolChest</code></li>
<li><code>org.apache.druid.query.QueryRunnerFactory</code></li>
</ol>
<p>Registering these uses the same general strategy as a deep storage mechanism does. You do something like</p>
<pre><code class="hljs css language-java">DruidBinders.queryToolChestBinder(binder)
.addBinding(SegmentMetadataQuery.class)
.to(SegmentMetadataQueryQueryToolChest.class);
DruidBinders.queryRunnerFactoryBinder(binder)
.addBinding(SegmentMetadataQuery.class)
.to(SegmentMetadataQueryRunnerFactory.class);
</code></pre>
<p>The first one binds the SegmentMetadataQueryQueryToolChest for usage when a SegmentMetadataQuery is used. The second one does the same thing but for the QueryRunnerFactory instead.</p>
<h3><a class="anchor" aria-hidden="true" id="adding-new-jersey-resources"></a><a href="#adding-new-jersey-resources" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding new Jersey resources</h3>
<p>Adding new Jersey resources to a module requires calling the following code to bind the resource in the module:</p>
<pre><code class="hljs css language-java">Jerseys.addResource(binder, NewResource.class);
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="adding-a-new-password-provider-implementation"></a><a href="#adding-a-new-password-provider-implementation" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Adding a new Password Provider implementation</h3>
<p>You will need to implement <code>org.apache.druid.metadata.PasswordProvider</code> interface. For every place where Druid uses PasswordProvider, a new instance of the implementation will be created,
thus make sure all the necessary information required for fetching each password is supplied during object instantiation.
In your implementation of <code>org.apache.druid.initialization.DruidModule</code>, <code>getJacksonModules</code> should look something like this -</p>
<pre><code class="hljs css language-java"> <span class="hljs-keyword">return</span> ImmutableList.of(
<span class="hljs-keyword">new</span> SimpleModule(<span class="hljs-string">"SomePasswordProviderModule"</span>)
.registerSubtypes(
<span class="hljs-keyword">new</span> NamedType(SomePasswordProvider.class, <span class="hljs-string">"some"</span>)
)
);
</code></pre>
<p>where <code>SomePasswordProvider</code> is the implementation of <code>PasswordProvider</code> interface, you can have a look at <code>org.apache.druid.metadata.EnvironmentVariablePasswordProvider</code> for example.</p>
<h3><a class="anchor" aria-hidden="true" id="bundle-your-extension-with-all-the-other-druid-extensions"></a><a href="#bundle-your-extension-with-all-the-other-druid-extensions" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Bundle your extension with all the other Druid extensions</h3>
<p>When you do <code>mvn install</code>, Druid extensions will be packaged within the Druid tarball and <code>extensions</code> directory, which are both underneath <code>distribution/target/</code>.</p>
<p>If you want your extension to be included, you can add your extension's maven coordinate as an argument at
<a href="https://github.com/apache/incubator-druid/blob/master/distribution/pom.xml#L95">distribution/pom.xml</a></p>
<p>During <code>mvn install</code>, maven will install your extension to the local maven repository, and then call <a href="/docs/latest/operations/pull-deps.html">pull-deps</a> to pull your extension from
there. In the end, you should see your extension underneath <code>distribution/target/extensions</code> and within Druid tarball.</p>
<h3><a class="anchor" aria-hidden="true" id="managing-dependencies"></a><a href="#managing-dependencies" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Managing dependencies</h3>
<p>Managing library collisions can be daunting for extensions which draw in commonly used libraries. Here is a list of group IDs for libraries that are suggested to be specified with a <code>provided</code> scope to prevent collision with versions used in druid:</p>
<pre><code class="hljs">"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.apache</span><span class="hljs-selector-class">.druid</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.metamx</span><span class="hljs-selector-class">.druid</span>",
"<span class="hljs-selector-tag">asm</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.ow2</span><span class="hljs-selector-class">.asm</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.jboss</span><span class="hljs-selector-class">.netty</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.google</span><span class="hljs-selector-class">.guava</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.google</span><span class="hljs-selector-class">.code</span><span class="hljs-selector-class">.findbugs</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.google</span><span class="hljs-selector-class">.protobuf</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.esotericsoftware</span><span class="hljs-selector-class">.minlog</span>",
"<span class="hljs-selector-tag">log4j</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.slf4j</span>",
"<span class="hljs-selector-tag">commons-logging</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.eclipse</span><span class="hljs-selector-class">.jetty</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.mortbay</span><span class="hljs-selector-class">.jetty</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.sun</span><span class="hljs-selector-class">.jersey</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.sun</span><span class="hljs-selector-class">.jersey</span><span class="hljs-selector-class">.contribs</span>",
"<span class="hljs-selector-tag">common-beanutils</span>",
"<span class="hljs-selector-tag">commons-codec</span>",
"<span class="hljs-selector-tag">commons-lang</span>",
"<span class="hljs-selector-tag">commons-cli</span>",
"<span class="hljs-selector-tag">commons-io</span>",
"<span class="hljs-selector-tag">javax</span><span class="hljs-selector-class">.activation</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.apache</span><span class="hljs-selector-class">.httpcomponents</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.apache</span><span class="hljs-selector-class">.zookeeper</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.codehaus</span><span class="hljs-selector-class">.jackson</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.fasterxml</span><span class="hljs-selector-class">.jackson</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.fasterxml</span><span class="hljs-selector-class">.jackson</span><span class="hljs-selector-class">.core</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.fasterxml</span><span class="hljs-selector-class">.jackson</span><span class="hljs-selector-class">.dataformat</span>",
"<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.fasterxml</span><span class="hljs-selector-class">.jackson</span><span class="hljs-selector-class">.datatype</span>",
"<span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.roaringbitmap</span>",
"<span class="hljs-selector-tag">net</span><span class="hljs-selector-class">.java</span><span class="hljs-selector-class">.dev</span><span class="hljs-selector-class">.jets3t</span>"
</code></pre>
<p>See the documentation in <code>org.apache.druid.cli.PullDependencies</code> for more information.</p>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/latest/development/overview.html"><span class="arrow-prev">← </span><span>Developing on Druid</span></a><a class="docs-next button" href="/docs/latest/development/javascript.html"><span class="function-name-prevnext">JavaScript functionality</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#writing-your-own-extensions">Writing your own extensions</a><ul class="toc-headings"><li><a href="#creating-a-druid-module">Creating a Druid Module</a></li><li><a href="#registering-your-druid-module">Registering your Druid Module</a></li><li><a href="#adding-a-new-deep-storage-implementation">Adding a new deep storage implementation</a></li><li><a href="#validating-your-deep-storage-implementation">Validating your deep storage implementation</a></li><li><a href="#adding-a-new-firehose">Adding a new Firehose</a></li><li><a href="#adding-aggregators">Adding Aggregators</a></li><li><a href="#adding-complex-metrics">Adding Complex Metrics</a></li><li><a href="#adding-new-query-types">Adding new Query types</a></li><li><a href="#adding-new-jersey-resources">Adding new Jersey resources</a></li><li><a href="#adding-a-new-password-provider-implementation">Adding a new Password Provider implementation</a></li><li><a href="#bundle-your-extension-with-all-the-other-druid-extensions">Bundle your extension with all the other Druid extensions</a></li><li><a href="#managing-dependencies">Managing dependencies</a></li></ul></li></ul></nav></div><footer class="nav-footer druid-footer" id="footer"><div class="container"><div class="text-center"><p><a href="/technology">Technology</a> · <a href="/use-cases">Use Cases</a> · <a href="/druid-powered">Powered by Druid</a> · <a href="/docs/latest/latest">Docs</a> · <a href="/community/">Community</a> · <a href="/downloads.html">Download</a> · <a href="/faq">FAQ</a></p></div><div class="text-center"><a title="Join the user group" href="https://groups.google.com/forum/#!forum/druid-user" target="_blank"><span class="fa fa-comments"></span></a> · <a title="Follow Druid" href="https://twitter.com/druidio" target="_blank"><span class="fab fa-twitter"></span></a> · <a title="Download via Apache" href="https://www.apache.org/dyn/closer.cgi?path=/incubator/druid/{{ site.druid_versions[0].versions[0].version }}/apache-druid-{{ site.druid_versions[0].versions[0].version }}-bin.tar.gz" target="_blank"><span class="fas fa-feather"></span></a> · <a title="GitHub" href="https://github.com/apache/incubator-druid" target="_blank"><span class="fab fa-github"></span></a></div><div class="text-center license">Copyright © 2019 <a href="https://www.apache.org/" target="_blank">Apache Software Foundation</a>.<br/>Except where otherwise noted, licensed under <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a>.<br/>Apache Druid, Druid, and the Druid logo are either registered trademarks or trademarks of The Apache Software Foundation in the United States and other countries.</div></div></footer></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>
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