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class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Release info</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><a class="breadcrumbs__link" itemprop="item" href="/docs/32.0.0/release-info/migration-guide"><span itemprop="name">Migration guides</span></a><meta itemprop="position" content="2"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Subquery limit</span><meta itemprop="position" content="3"></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>Migration guide: Subquery limit</h1></header><p>Druid now allows you to set a byte-based limit on subquery size, to prevent brokers from running out of memory when handling large subqueries. |
| Druid uses subqueries as joins as well as in common table expressions, such as WITH.</p><p>The byte-based subquery limit overrides Druid's row-based subquery limit.</p><div class="theme-admonition theme-admonition-info alert alert--info admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 14 16"><path fill-rule="evenodd" d="M7 2.3c3.14 0 5.7 2.56 5.7 5.7s-2.56 5.7-5.7 5.7A5.71 5.71 0 0 1 1.3 8c0-3.14 2.56-5.7 5.7-5.7zM7 1C3.14 1 0 4.14 0 8s3.14 7 7 7 7-3.14 7-7-3.14-7-7-7zm1 3H6v5h2V4zm0 6H6v2h2v-2z"></path></svg></span>info</div><div class="admonitionContent_S0QG"><p>We recommend that you move towards using byte-based limits starting in Druid 30.0.</p></div></div><p>For queries that generate a large number of rows (5 million or more), we recommend that you don't use <code>maxSubqueryBytes</code> from the outset. |
| You can increase <code>maxSubqueryRows</code> and then configure the byte-based limit if you find that Druid needs it to process the query.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="row-based-subquery-limit">Row-based subquery limit<a href="#row-based-subquery-limit" class="hash-link" aria-label="Direct link to Row-based subquery limit" title="Direct link to Row-based subquery limit"></a></h2><p>Druid uses the <code>maxSubqueryRows</code> property to limit the number of rows Druid returns in a subquery. |
| Because this is a row-based limit, it doesn't restrict the overall size of the returned data.</p><p>The <code>maxSubqueryRows</code> property is set to 100,000 by default.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="enable-a-byte-based-subquery-limit">Enable a byte-based subquery limit<a href="#enable-a-byte-based-subquery-limit" class="hash-link" aria-label="Direct link to Enable a byte-based subquery limit" title="Direct link to Enable a byte-based subquery limit"></a></h2><p>Set the optional property <code>maxSubqueryBytes</code> to set a maximum number of returned bytes. |
| This property takes precedence over <code>maxSubqueryRows</code>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="usage-considerations">Usage considerations<a href="#usage-considerations" class="hash-link" aria-label="Direct link to Usage considerations" title="Direct link to Usage considerations"></a></h2><p>You can set both <code>maxSubqueryRows</code> and <code>maxSubqueryBytes</code> at cluster level and override them in individual queries. |
| See <a href="/docs/32.0.0/configuration#overriding-default-query-context-values">Overriding default query context values</a> for more information.</p><p>Make sure you enable the Broker monitor <code>SubqueryCountStatsMonitor</code> so that Druid emits metrics for subquery statistics. |
| To do this, add <code>org.apache.druid.server.metrics.SubqueryCountStatsMonitor</code> to the <code>druid.monitoring.monitors</code> property in your Broker's <code>runtime.properties</code> configuration file. |
| See <a href="/docs/32.0.0/configuration/#metrics-monitors">Metrics monitors</a> for more information.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="learn-more">Learn more<a href="#learn-more" class="hash-link" aria-label="Direct link to Learn more" title="Direct link to Learn more"></a></h2><p>See the following topics for more information:</p><ul><li><a href="/docs/32.0.0/querying/query-context">Query context</a> for information on setting query context parameters.</li><li><a href="/docs/32.0.0/configuration#guardrails-for-materialization-of-subqueries">Broker configuration reference</a> for more information on <code>maxSubqueryRows</code> and <code>maxSubqueryBytes</code>.</li></ul></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/32.0.0/release-info/migr-front-coded-dict"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Front-coded dictionaries</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/32.0.0/release-info/migr-ansi-sql-null"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">SQL compliant mode</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="#row-based-subquery-limit" class="table-of-contents__link toc-highlight">Row-based subquery limit</a></li><li><a href="#enable-a-byte-based-subquery-limit" class="table-of-contents__link toc-highlight">Enable a byte-based subquery limit</a></li><li><a href="#usage-considerations" class="table-of-contents__link toc-highlight">Usage considerations</a></li><li><a href="#learn-more" class="table-of-contents__link toc-highlight">Learn more</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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