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<p>Apache Druid relies on an external dependency for metadata storage.
Druid uses the metadata store to house various metadata about the system, but not to store the actual data.
The metadata store retains all metadata essential for a Druid cluster to work.</p>
<p>The metadata store includes the following:</p>
<ul>
<li>Segments records</li>
<li>Rule records</li>
<li>Configuration records</li>
<li>Task-related tables</li>
<li>Audit records</li>
</ul>
<p>Derby is the default metadata store for Druid, however, it is not suitable for production.
<a href="/docs/latest/development/extensions-core/mysql.html">MySQL</a> and <a href="/docs/latest/development/extensions-core/postgresql.html">PostgreSQL</a> are more production suitable metadata stores.
See <a href="/docs/latest/configuration/index.html#metadata-storage">Metadata storage configuration</a> for the default configuration settings.</p>
<blockquote>
<p>We also recommend you set up a high availability environment because there is no way to restore lost metadata.</p>
</blockquote>
<h2><a class="anchor" aria-hidden="true" id="available-metadata-stores"></a><a href="#available-metadata-stores" 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>Available metadata stores</h2>
<p>Druid supports Derby, MySQL, and PostgreSQL for storing metadata.</p>
<h3><a class="anchor" aria-hidden="true" id="derby"></a><a href="#derby" 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>Derby</h3>
<blockquote>
<p>For production clusters, consider using MySQL or PostgreSQL instead of Derby.</p>
</blockquote>
<p>Configure metadata storage with Derby by setting the following properties in your Druid configuration.</p>
<pre><code class="hljs css language-properties"><span class="hljs-meta">druid.metadata.storage.type</span>=<span class="hljs-string">derby</span>
<span class="hljs-meta">druid.metadata.storage.connector.connectURI</span>=<span class="hljs-string">jdbc:derby://localhost:1527//opt/var/druid_state/derby;create=true</span>
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="mysql"></a><a href="#mysql" 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>MySQL</h3>
<p>See <a href="/docs/latest/development/extensions-core/mysql.html">mysql-metadata-storage extension documentation</a>.</p>
<h3><a class="anchor" aria-hidden="true" id="postgresql"></a><a href="#postgresql" 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>PostgreSQL</h3>
<p>See <a href="/docs/latest/development/extensions-core/postgresql.html">postgresql-metadata-storage</a>.</p>
<h2><a class="anchor" aria-hidden="true" id="adding-custom-dbcp-properties"></a><a href="#adding-custom-dbcp-properties" 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 custom DBCP properties</h2>
<p>You can add custom properties to customize the database connection pool (DBCP) for connecting to the metadata store.
Define these properties with a <code>druid.metadata.storage.connector.dbcp.</code> prefix.
For example:</p>
<pre><code class="hljs css language-properties"><span class="hljs-meta">druid.metadata.storage.connector.dbcp.maxConnLifetimeMillis</span>=<span class="hljs-string">1200000</span>
<span class="hljs-meta">druid.metadata.storage.connector.dbcp.defaultQueryTimeout</span>=<span class="hljs-string">30000</span>
</code></pre>
<p>Certain properties cannot be set through <code>druid.metadata.storage.connector.dbcp.</code> and must be set with the prefix <code>druid.metadata.storage.connector.</code>:</p>
<ul>
<li><code>username</code></li>
<li><code>password</code></li>
<li><code>connectURI</code></li>
<li><code>validationQuery</code></li>
<li><code>testOnBorrow</code></li>
</ul>
<p>See <a href="https://commons.apache.org/proper/commons-dbcp/configuration">BasicDataSource Configuration</a> for a full list of configurable properties.</p>
<h2><a class="anchor" aria-hidden="true" id="metadata-storage-tables"></a><a href="#metadata-storage-tables" 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>Metadata storage tables</h2>
<p>This section describes the various tables in metadata storage.</p>
<h3><a class="anchor" aria-hidden="true" id="segments-table"></a><a href="#segments-table" 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>Segments table</h3>
<p>This is dictated by the <code>druid.metadata.storage.tables.segments</code> property.</p>
<p>This table stores metadata about the segments that should be available in the system. (This set of segments is called
&quot;used segments&quot; elsewhere in the documentation and throughout the project.) The table is polled by the
<a href="/docs/latest/design/coordinator.html">Coordinator</a> to determine the set of segments that should be available for querying in the
system. The table has two main functional columns, the other columns are for indexing purposes.</p>
<p>Value 1 in the <code>used</code> column means that the segment should be &quot;used&quot; by the cluster (i.e., it should be loaded and
available for requests). Value 0 means that the segment should not be loaded into the cluster. We do this as a means of
unloading segments from the cluster without actually removing their metadata (which allows for simpler rolling back if
that is ever an issue).</p>
<p>The <code>payload</code> column stores a JSON blob that has all of the metadata for the segment.
Some of the data in the <code>payload</code> column intentionally duplicates data from other columns in the segments table.
As an example, the <code>payload</code> column may take the following form:</p>
<pre><code class="hljs css language-json">{
 <span class="hljs-attr">"dataSource"</span>:<span class="hljs-string">"wikipedia"</span>,
 <span class="hljs-attr">"interval"</span>:<span class="hljs-string">"2012-05-23T00:00:00.000Z/2012-05-24T00:00:00.000Z"</span>,
 <span class="hljs-attr">"version"</span>:<span class="hljs-string">"2012-05-24T00:10:00.046Z"</span>,
 <span class="hljs-attr">"loadSpec"</span>:{
    <span class="hljs-attr">"type"</span>:<span class="hljs-string">"s3_zip"</span>,
    <span class="hljs-attr">"bucket"</span>:<span class="hljs-string">"bucket_for_segment"</span>,
    <span class="hljs-attr">"key"</span>:<span class="hljs-string">"path/to/segment/on/s3"</span>
 },
 <span class="hljs-attr">"dimensions"</span>:<span class="hljs-string">"comma-delimited-list-of-dimension-names"</span>,
 <span class="hljs-attr">"metrics"</span>:<span class="hljs-string">"comma-delimited-list-of-metric-names"</span>,
 <span class="hljs-attr">"shardSpec"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"none"</span>},
 <span class="hljs-attr">"binaryVersion"</span>:<span class="hljs-number">9</span>,
 <span class="hljs-attr">"size"</span>:size_of_segment,
 <span class="hljs-attr">"identifier"</span>:<span class="hljs-string">"wikipedia_2012-05-23T00:00:00.000Z_2012-05-24T00:00:00.000Z_2012-05-23T00:10:00.046Z"</span>
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="rule-table"></a><a href="#rule-table" 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>Rule table</h3>
<p>The rule table stores the various rules about where segments should
land. These rules are used by the <a href="/docs/latest/design/coordinator.html">Coordinator</a>
when making segment (re-)allocation decisions about the cluster.</p>
<h3><a class="anchor" aria-hidden="true" id="config-table"></a><a href="#config-table" 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>Config table</h3>
<p>The config table stores runtime configuration objects. We do not have
many of these yet and we are not sure if we will keep this mechanism going
forward, but it is the beginnings of a method of changing some configuration
parameters across the cluster at runtime.</p>
<h3><a class="anchor" aria-hidden="true" id="task-related-tables"></a><a href="#task-related-tables" 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>Task-related tables</h3>
<p>Task-related tables are created and used by the <a href="/docs/latest/design/overlord.html">Overlord</a> and <a href="/docs/latest/design/middlemanager.html">MiddleManager</a> when managing tasks.</p>
<h3><a class="anchor" aria-hidden="true" id="audit-table"></a><a href="#audit-table" 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>Audit table</h3>
<p>The audit table stores the audit history for configuration changes
such as rule changes done by <a href="/docs/latest/design/coordinator.html">Coordinator</a> and other
config changes.</p>
<h2><a class="anchor" aria-hidden="true" id="metadata-storage-access"></a><a href="#metadata-storage-access" 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>Metadata storage access</h2>
<p>Only the following processes access the metadata storage:</p>
<ol>
<li>Indexing service processes (if any)</li>
<li>Realtime processes (if any)</li>
<li>Coordinator processes</li>
</ol>
<p>Thus you need to give permissions (e.g., in AWS security groups) for only these machines to access the metadata storage.</p>
<h2><a class="anchor" aria-hidden="true" id="learn-more"></a><a href="#learn-more" 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>Learn more</h2>
<p>See the following topics for more information:</p>
<ul>
<li><a href="/docs/latest/configuration/index.html#metadata-storage">Metadata storage configuration</a></li>
<li><a href="/docs/latest/operations/clean-metadata-store.html">Automated cleanup for metadata records</a></li>
</ul>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/latest/dependencies/deep-storage.html"><span class="arrow-prev">← </span><span>Deep storage</span></a><a class="docs-next button" href="/docs/latest/dependencies/zookeeper.html"><span class="function-name-prevnext">ZooKeeper</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#available-metadata-stores">Available metadata stores</a><ul class="toc-headings"><li><a href="#derby">Derby</a></li><li><a href="#mysql">MySQL</a></li><li><a href="#postgresql">PostgreSQL</a></li></ul></li><li><a href="#adding-custom-dbcp-properties">Adding custom DBCP properties</a></li><li><a href="#metadata-storage-tables">Metadata storage tables</a><ul class="toc-headings"><li><a href="#segments-table">Segments table</a></li><li><a href="#rule-table">Rule table</a></li><li><a href="#config-table">Config table</a></li><li><a href="#task-related-tables">Task-related tables</a></li><li><a href="#audit-table">Audit table</a></li></ul></li><li><a href="#metadata-storage-access">Metadata storage access</a></li><li><a href="#learn-more">Learn more</a></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/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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