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class="search-icon" tabindex="0"></span><input type="search" id="search_input_react" placeholder="Loading..." aria-label="Search" class="navbar__search-input search-bar" disabled=""></div></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div id="__docusaurus_skipToContent_fallback" class="main-wrapper mainWrapper_z2l0 docsWrapper_BCFX"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_sjWU" type="button"></button><div class="docPage__5DB"><main class="docMainContainer_gTbr docMainContainerEnhanced_Uz_u"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><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>Cached Lookup Module</h1></header><h2 class="anchor anchorWithStickyNavbar_LWe7" id="description">Description<a href="#description" class="hash-link" aria-label="Direct link to Description" title="Direct link to Description"></a></h2><p>This Apache Druid module provides a per-lookup caching mechanism for JDBC data sources.
 The main goal of this cache is to speed up the access to a high latency lookup sources and to provide a caching isolation for every lookup source.
 Thus user can define various caching strategies or and implementation per lookup, even if the source is the same.
 This module can be used side to side with other lookup module like the global cached lookup module.</p><p>To use this Apache Druid extension, <a href="/docs/28.0.0/configuration/extensions#loading-extensions">include</a> <code>druid-lookups-cached-single</code> in the extensions load list.</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> If using JDBC, you will need to add your database&#x27;s client JAR files to the extension&#x27;s directory.
 For Postgres, the connector JAR is already included.
 See the MySQL extension documentation for instructions to obtain <a href="/docs/28.0.0/development/extensions-core/mysql#installing-the-mysql-connector-library">MySQL</a> or <a href="/docs/28.0.0/development/extensions-core/mysql#alternative-installing-the-mariadb-connector-library">MariaDB</a> connector libraries.
 Copy or symlink the downloaded file to <code>extensions/druid-lookups-cached-single</code> under the distribution root directory.</p></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="architecture">Architecture<a href="#architecture" class="hash-link" aria-label="Direct link to Architecture" title="Direct link to Architecture"></a></h2><p>Generally speaking this module can be divided into two main component, namely, the data fetcher layer and caching layer.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="data-fetcher-layer">Data Fetcher layer<a href="#data-fetcher-layer" class="hash-link" aria-label="Direct link to Data Fetcher layer" title="Direct link to Data Fetcher layer"></a></h3><p>First part is the data fetcher layer API <code>DataFetcher</code>, that exposes a set of fetch methods to fetch data from the actual Lookup dimension source.
 For instance <code>JdbcDataFetcher</code> provides an implementation of <code>DataFetcher</code> that can be used to fetch key/value from a RDBMS via JDBC driver.
 If you need new type of data fetcher, all you need to do, is to implement the interface <code>DataFetcher</code> and load it via another druid module.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="caching-layer">Caching layer<a href="#caching-layer" class="hash-link" aria-label="Direct link to Caching layer" title="Direct link to Caching layer"></a></h3><p>This extension comes with two different caching strategies. First strategy is a poll based and the second is a load based.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="poll-lookup-cache">Poll lookup cache<a href="#poll-lookup-cache" class="hash-link" aria-label="Direct link to Poll lookup cache" title="Direct link to Poll lookup cache"></a></h4><p>The poll strategy cache strategy will fetch and swap all the pair of key/values periodically from the lookup source.
 Hence, user should make sure that the cache can fit all the data.
 The current implementation provides 2 type of poll cache, the first is on-heap (uses immutable map), while the second uses MapDB based off-heap map.
 User can also implement a different lookup polling cache by implementing <code>PollingCacheFactory</code> and <code>PollingCache</code> interfaces.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="loading-lookup">Loading lookup<a href="#loading-lookup" class="hash-link" aria-label="Direct link to Loading lookup" title="Direct link to Loading lookup"></a></h4><p>Loading cache strategy will load the key/value pair upon request on the key it self, the general algorithm is load key if absent.
 Once the key/value  pair is loaded eviction will occur according to the cache eviction policy.
 This module comes with two loading lookup implementation, the first is on-heap backed by a Guava cache implementation, the second is MapDB off-heap implementation.
 Both implementations offer various eviction strategies.
 Same for Loading cache, developer can implement a new type of loading cache by implementing <code>LookupLoadingCache</code> interface.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="configuration-and-operation">Configuration and Operation:<a href="#configuration-and-operation" class="hash-link" aria-label="Direct link to Configuration and Operation:" title="Direct link to Configuration and Operation:"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="polling-lookup">Polling Lookup<a href="#polling-lookup" class="hash-link" aria-label="Direct link to Polling Lookup" title="Direct link to Polling Lookup"></a></h3><p><strong>Note that the current implementation of <code>offHeapPolling</code> and <code>onHeapPolling</code> will create two caches one to lookup value based on key and the other to reverse lookup the key from value</strong></p><table><thead><tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr></thead><tbody><tr><td>dataFetcher</td><td>JSON object</td><td>Specifies the lookup data fetcher type for fetching data</td><td>yes</td><td>null</td></tr><tr><td>cacheFactory</td><td>JSON Object</td><td>Cache factory implementation</td><td>no</td><td>onHeapPolling</td></tr><tr><td>pollPeriod</td><td>Period</td><td>polling period</td><td>no</td><td>null (poll once)</td></tr></tbody></table><h5 class="anchor anchorWithStickyNavbar_LWe7" id="example-of-polling-on-heap-lookup">Example of Polling On-heap Lookup<a href="#example-of-polling-on-heap-lookup" class="hash-link" aria-label="Direct link to Example of Polling On-heap Lookup" title="Direct link to Example of Polling On-heap Lookup"></a></h5><p>This example demonstrates a polling cache that will update its on-heap cache every 10 minutes</p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">    </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;pollingLookup&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;pollPeriod&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;PT10M&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;dataFetcher&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"> </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbcDataFetcher&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;connectorConfig&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbc://mysql://localhost:3306/my_data_base&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;table&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;lookup_table_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;keyColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;key_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;valueColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;value_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;cacheFactory&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;onHeapPolling&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain" style="display:inline-block"></span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h5 class="anchor anchorWithStickyNavbar_LWe7" id="example-polling-off-heap-lookup">Example Polling Off-heap Lookup<a href="#example-polling-off-heap-lookup" class="hash-link" aria-label="Direct link to Example Polling Off-heap Lookup" title="Direct link to Example Polling Off-heap Lookup"></a></h5><p>This example demonstrates an off-heap lookup that will be cached once and never swapped <code>(pollPeriod == null)</code></p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">    </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;pollingLookup&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;dataFetcher&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"> </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbcDataFetcher&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;connectorConfig&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbc://mysql://localhost:3306/my_data_base&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;table&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;lookup_table_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;keyColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;key_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;valueColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;value_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;cacheFactory&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;offHeapPolling&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain" style="display:inline-block"></span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="loading-lookup-1">Loading lookup<a href="#loading-lookup-1" class="hash-link" aria-label="Direct link to Loading lookup" title="Direct link to Loading lookup"></a></h3><table><thead><tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr></thead><tbody><tr><td>dataFetcher</td><td>JSON object</td><td>Specifies the lookup data fetcher type  to use in order to fetch data</td><td>yes</td><td>null</td></tr><tr><td>loadingCacheSpec</td><td>JSON Object</td><td>Lookup cache spec implementation</td><td>yes</td><td>null</td></tr><tr><td>reverseLoadingCacheSpec</td><td>JSON Object</td><td>Reverse lookup cache  implementation</td><td>yes</td><td>null</td></tr></tbody></table><h5 class="anchor anchorWithStickyNavbar_LWe7" id="example-loading-on-heap-guava">Example Loading On-heap Guava<a href="#example-loading-on-heap-guava" class="hash-link" aria-label="Direct link to Example Loading On-heap Guava" title="Direct link to Example Loading On-heap Guava"></a></h5><p>Guava cache configuration spec.</p><table><thead><tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr></thead><tbody><tr><td>concurrencyLevel</td><td>int</td><td>Allowed concurrency among update operations</td><td>no</td><td>4</td></tr><tr><td>initialCapacity</td><td>int</td><td>Initial capacity size</td><td>no</td><td>null</td></tr><tr><td>maximumSize</td><td>long</td><td>Specifies the maximum number of entries the cache may contain.</td><td>no</td><td>null (infinite capacity)</td></tr><tr><td>expireAfterAccess</td><td>long</td><td>Specifies the eviction time after last read in milliseconds.</td><td>no</td><td>null (No read-time-based eviction when set to null)</td></tr><tr><td>expireAfterWrite</td><td>long</td><td>Specifies the eviction time after last write in milliseconds.</td><td>no</td><td>null (No write-time-based eviction when set to null)</td></tr></tbody></table><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;loadingLookup&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;dataFetcher&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"> </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbcDataFetcher&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;connectorConfig&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbc://mysql://localhost:3306/my_data_base&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;table&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;lookup_table_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;keyColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;key_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;valueColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;value_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;loadingCacheSpec&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;guava&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;reverseLoadingCacheSpec&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;guava&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;maximumSize&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">500000</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;expireAfterAccess&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">100000</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;expireAfterWrite&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">10000</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h5 class="anchor anchorWithStickyNavbar_LWe7" id="example-loading-off-heap-mapdb">Example Loading Off-heap MapDB<a href="#example-loading-off-heap-mapdb" class="hash-link" aria-label="Direct link to Example Loading Off-heap MapDB" title="Direct link to Example Loading Off-heap MapDB"></a></h5><p>Off heap cache is backed by <a href="http://www.mapdb.org/" target="_blank" rel="noopener noreferrer">MapDB</a> implementation. MapDB is using direct memory as memory pool, please take that into account when limiting the JVM direct memory setup.</p><table><thead><tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr></thead><tbody><tr><td>maxStoreSize</td><td>double</td><td>maximal size of store in GiB, if store is larger entries will start expiring</td><td>no</td><td>0</td></tr><tr><td>maxEntriesSize</td><td>long</td><td>Specifies the maximum number of entries the cache may contain.</td><td>no</td><td>0 (infinite capacity)</td></tr><tr><td>expireAfterAccess</td><td>long</td><td>Specifies the eviction time after last read in milliseconds.</td><td>no</td><td>0 (No read-time-based eviction when set to null)</td></tr><tr><td>expireAfterWrite</td><td>long</td><td>Specifies the eviction time after last write in milliseconds.</td><td>no</td><td>0 (No write-time-based eviction when set to null)</td></tr></tbody></table><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;loadingLookup&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;dataFetcher&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"> </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbcDataFetcher&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;connectorConfig&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;jdbc://mysql://localhost:3306/my_data_base&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;table&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;lookup_table_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;keyColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;key_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;valueColumn&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;value_column_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;loadingCacheSpec&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;mapDb&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;maxEntriesSize&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">100000</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">   </span><span class="token property">&quot;reverseLoadingCacheSpec&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token string" style="color:rgb(195, 232, 141)">&quot;mapDb&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;maxStoreSize&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">5</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;expireAfterAccess&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">100000</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;expireAfterWrite&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token number" style="color:rgb(247, 140, 108)">10000</span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="jdbc-data-fetcher">JDBC Data Fetcher<a href="#jdbc-data-fetcher" class="hash-link" aria-label="Direct link to JDBC Data Fetcher" title="Direct link to JDBC Data Fetcher"></a></h3><table><thead><tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr></thead><tbody><tr><td><code>connectorConfig</code></td><td>JSON object</td><td>Specifies the database connection details. You can set <code>connectURI</code>, <code>user</code> and <code>password</code>. You can selectively allow JDBC properties in <code>connectURI</code>. See <a href="/docs/28.0.0/configuration/#jdbc-connections-to-external-databases">JDBC connections security config</a> for more details.</td><td>yes</td><td></td></tr><tr><td><code>table</code></td><td>string</td><td>The table name to read from.</td><td>yes</td><td></td></tr><tr><td><code>keyColumn</code></td><td>string</td><td>The column name that contains the lookup key.</td><td>yes</td><td></td></tr><tr><td><code>valueColumn</code></td><td>string</td><td>The column name that contains the lookup value.</td><td>yes</td><td></td></tr><tr><td><code>streamingFetchSize</code></td><td>int</td><td>Fetch size used in JDBC connections.</td><td>no</td><td>1000</td></tr></tbody></table></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"></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="#description" class="table-of-contents__link toc-highlight">Description</a></li><li><a href="#architecture" class="table-of-contents__link toc-highlight">Architecture</a><ul><li><a href="#data-fetcher-layer" class="table-of-contents__link toc-highlight">Data Fetcher layer</a></li><li><a href="#caching-layer" class="table-of-contents__link toc-highlight">Caching layer</a></li></ul></li><li><a href="#configuration-and-operation" class="table-of-contents__link toc-highlight">Configuration and Operation:</a><ul><li><a href="#polling-lookup" class="table-of-contents__link toc-highlight">Polling Lookup</a></li><li><a href="#loading-lookup-1" class="table-of-contents__link toc-highlight">Loading lookup</a></li><li><a href="#jdbc-data-fetcher" class="table-of-contents__link toc-highlight">JDBC Data Fetcher</a></li></ul></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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