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| <p>This page discusses how to use JavaScript to extend Apache Druid.</p> |
| <h2><a class="anchor" aria-hidden="true" id="examples"></a><a href="#examples" 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>Examples</h2> |
| <p>JavaScript can be used to extend Druid in a variety of ways:</p> |
| <ul> |
| <li><a href="../querying/aggregations.html#javascript-aggregator">Aggregators</a></li> |
| <li><a href="../querying/dimensionspecs.html#javascript-extraction-function">Extraction functions</a></li> |
| <li><a href="../querying/filters.html#javascript-filter">Filters</a></li> |
| <li><a href="../querying/post-aggregations.html#javascript-post-aggregator">Post-aggregators</a></li> |
| <li><a href="../ingestion/data-formats.html#javascript-parsespec">Input parsers</a></li> |
| <li><a href="../design/router.html#javascript">Router strategy</a></li> |
| <li><a href="../configuration/index.html#javascript-worker-select-strategy">Worker select strategy</a></li> |
| </ul> |
| <p>JavaScript can be injected dynamically at runtime, making it convenient to rapidly prototype new functionality |
| without needing to write and deploy Druid extensions.</p> |
| <p>Druid uses the Mozilla Rhino engine at optimization level 9 to compile and execute JavaScript.</p> |
| <h2><a class="anchor" aria-hidden="true" id="security"></a><a href="#security" 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>Security</h2> |
| <p>Druid does not execute JavaScript functions in a sandbox, so they have full access to the machine. So JavaScript |
| functions allow users to execute arbitrary code inside druid process. So, by default, JavaScript is disabled. |
| However, on dev/staging environments or secured production environments you can enable those by setting |
| the <a href="../configuration/index.html#javascript">configuration property</a> |
| <code>druid.javascript.enabled = true</code>.</p> |
| <h2><a class="anchor" aria-hidden="true" id="global-variables"></a><a href="#global-variables" 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>Global variables</h2> |
| <p>Avoid using global variables. Druid may share the global scope between multiple threads, which can lead to |
| unpredictable results if global variables are used.</p> |
| <h2><a class="anchor" aria-hidden="true" id="performance"></a><a href="#performance" 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>Performance</h2> |
| <p>Simple JavaScript functions typically have a slight performance penalty to native speed. More complex JavaScript |
| functions can have steeper performance penalties. Druid compiles JavaScript functions once on each data process per query.</p> |
| <p>You may need to pay special attention to garbage collection when making heavy use of JavaScript functions, especially |
| garbage collection of the compiled classes themselves. Be sure to use a garbage collector configuration that supports |
| timely collection of unused classes (this is generally easier on JDK8 with the Metaspace than it is on JDK7).</p> |
| <h2><a class="anchor" aria-hidden="true" id="javascript-vs-native-extensions"></a><a href="#javascript-vs-native-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>JavaScript vs. Native Extensions</h2> |
| <p>Generally we recommend using JavaScript when security is not an issue, and when speed of development is more important |
| than performance or memory use. If security is an issue, or if performance and memory use are of the utmost importance, |
| we recommend developing a native Druid extension.</p> |
| <p>In addition, native Druid extensions are more flexible than JavaScript functions. There are some kinds of extensions |
| (like sketches) that must be written as native Druid extensions due to their need for custom data formats.</p> |
| </span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/latest/development/modules.html"><span class="arrow-prev">← </span><span>Creating extensions</span></a><a class="docs-next button" href="/docs/latest/development/build.html"><span>Build from source</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#examples">Examples</a></li><li><a href="#security">Security</a></li><li><a href="#global-variables">Global variables</a></li><li><a href="#performance">Performance</a></li><li><a href="#javascript-vs-native-extensions">JavaScript vs. Native Extensions</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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