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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 breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Migration guides</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>Migration guides</h1></header><p>In general, when we introduce new features and behaviors into Apache Druid, we make every effort to avoid breaking existing features when introducing new behaviors. However, sometimes there are either bugs or performance limitations with the old behaviors that are not possible to fix in a backward-compatible way. In these cases, we must introduce breaking changes for the future maintainability of Druid. </p><p>The guides in this section outline breaking changes introduced in Druid 25.0.0 and later. Each guide provides instructions to migrate to new features.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="migrate-from-multi-value-dimensions-to-arrays">Migrate from multi-value dimensions to arrays<a href="#migrate-from-multi-value-dimensions-to-arrays" class="hash-link" aria-label="Direct link to Migrate from multi-value dimensions to arrays" title="Direct link to Migrate from multi-value dimensions to arrays"></a></h2><p>Druid now supports SQL-compliant array types. Whenever possible, you should use the array type over multi-value dimensions. See <a href="/docs/latest/release-info/migr-mvd-array">Migration guide: MVDs to arrays</a>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="migrate-to-front-coded-dictionary-encoding">Migrate to front-coded dictionary encoding<a href="#migrate-to-front-coded-dictionary-encoding" class="hash-link" aria-label="Direct link to Migrate to front-coded dictionary encoding" title="Direct link to Migrate to front-coded dictionary encoding"></a></h2><p>Druid encodes string columns into dictionaries for better compression. Front-coded dictionary encoding reduces storage and improves performance by optimizing for strings that share similar beginning substrings. See <a href="/docs/latest/release-info/migr-front-coded-dict">Migration guide: front-coded dictionaries</a> for more information.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="migrate-from-maxsubqueryrows-to-maxsubquerybytes">Migrate from <code>maxSubqueryRows</code> to <code>maxSubqueryBytes</code><a href="#migrate-from-maxsubqueryrows-to-maxsubquerybytes" class="hash-link" aria-label="Direct link to migrate-from-maxsubqueryrows-to-maxsubquerybytes" title="Direct link to migrate-from-maxsubqueryrows-to-maxsubquerybytes"></a></h2><p>Druid allows you to set a byte-based limit on subquery size to prevent Brokers from running out of memory when handling large subqueries. The byte-based subquery limit overrides Druid's row-based subquery limit. We recommend that you move towards using byte-based limits starting in Druid 30.0.0. See <a href="/docs/latest/release-info/migr-subquery-limit">Migration guide: subquery limit</a> for more information.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="migrate-to-sql-compliant-null-handling-mode">Migrate to SQL compliant null handling mode<a href="#migrate-to-sql-compliant-null-handling-mode" class="hash-link" aria-label="Direct link to Migrate to SQL compliant null handling mode" title="Direct link to Migrate to SQL compliant null handling mode"></a></h2><p>By default, the Druid <a href="/docs/latest/querying/sql-data-types#null-values">null handling</a> mode is now compliant with ANSI SQL. |
| This guide provides strategies for Druid operators and users who rely on the legacy Druid null handling behavior in their applications to transition to ANSI SQL compliant mode. See <a href="/docs/latest/release-info/migr-ansi-sql-null">Migration guide: SQL compliant mode</a> for more information.</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/latest/release-info/upgrade-notes"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Upgrade notes</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/latest/release-info/migr-mvd-array"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">MVDs to arrays</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="#migrate-from-multi-value-dimensions-to-arrays" class="table-of-contents__link toc-highlight">Migrate from multi-value dimensions to arrays</a></li><li><a href="#migrate-to-front-coded-dictionary-encoding" class="table-of-contents__link toc-highlight">Migrate to front-coded dictionary encoding</a></li><li><a href="#migrate-from-maxsubqueryrows-to-maxsubquerybytes" class="table-of-contents__link toc-highlight">Migrate from <code>maxSubqueryRows</code> to <code>maxSubqueryBytes</code></a></li><li><a href="#migrate-to-sql-compliant-null-handling-mode" class="table-of-contents__link toc-highlight">Migrate to SQL compliant null handling mode</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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