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fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Development</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">JavaScript functionality</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>JavaScript programming guide</h1></header><p>This page discusses how to use JavaScript to extend Apache Druid.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="examples">Examples<a href="#examples" class="hash-link" aria-label="Direct link to Examples" title="Direct link to Examples"></a></h2><p>JavaScript can be used to extend Druid in a variety of ways:</p><ul><li><a href="/docs/29.0.0/querying/aggregations#javascript-aggregator">Aggregators</a></li><li><a href="/docs/29.0.0/querying/dimensionspecs#javascript-extraction-function">Extraction functions</a></li><li><a href="/docs/29.0.0/querying/filters#javascript-filter">Filters</a></li><li><a href="/docs/29.0.0/querying/post-aggregations#javascript-post-aggregator">Post-aggregators</a></li><li><a href="/docs/29.0.0/ingestion/data-formats#javascript-parsespec">Input parsers</a></li><li><a href="/docs/29.0.0/design/router#javascript">Router strategy</a></li><li><a href="/docs/29.0.0/configuration/#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 class="anchor anchorWithStickyNavbar_LWe7" id="security">Security<a href="#security" class="hash-link" aria-label="Direct link to Security" title="Direct link to Security"></a></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="/docs/29.0.0/configuration/#javascript">configuration property</a> |
| <code>druid.javascript.enabled = true</code>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="global-variables">Global variables<a href="#global-variables" class="hash-link" aria-label="Direct link to Global variables" title="Direct link to Global variables"></a></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 class="anchor anchorWithStickyNavbar_LWe7" id="performance">Performance<a href="#performance" class="hash-link" aria-label="Direct link to Performance" title="Direct link to Performance"></a></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 class="anchor anchorWithStickyNavbar_LWe7" id="javascript-vs-native-extensions">JavaScript vs. Native Extensions<a href="#javascript-vs-native-extensions" class="hash-link" aria-label="Direct link to JavaScript vs. Native Extensions" title="Direct link to JavaScript vs. Native Extensions"></a></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></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/29.0.0/development/modules"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Creating extensions</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/29.0.0/development/build"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Build from source</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#examples" class="table-of-contents__link toc-highlight">Examples</a></li><li><a href="#security" class="table-of-contents__link toc-highlight">Security</a></li><li><a href="#global-variables" class="table-of-contents__link toc-highlight">Global variables</a></li><li><a href="#performance" class="table-of-contents__link toc-highlight">Performance</a></li><li><a href="#javascript-vs-native-extensions" class="table-of-contents__link toc-highlight">JavaScript vs. Native Extensions</a></li></ul></div></div></div></div></main></div></div><footer class="footer"><div class="container container-fluid"><div class="footer__bottom text--center"><div class="margin-bottom--sm"><img src="/img/favicon.png" class="themedImage_ToTc themedImage--light_HNdA footer__logo"><img src="/img/favicon.png" class="themedImage_ToTc themedImage--dark_i4oU footer__logo"></div><div class="footer__copyright">Copyright © 2023 Apache Software Foundation. Except where otherwise noted, licensed under CC BY-SA 4.0. 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></div></footer></div> |
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