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aria-label="Configuration-Parameters"><!---->Configuration-Parameters<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Monitor and Alert</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Administration Management</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Maintenance Tools</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Collaboration of Edge and Cloud</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Ecosystem Integration</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Cluster</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">FAQ</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">Reference</span><span class="arrow end"></span></button><!----></section></li></ul><!--[--><!----><!--]--></aside><!--[--><main class="page" id="main-content"><!--[--><!----><nav class="breadcrumb disable"></nav><div class="page-title"><h1><!---->Instructions</h1><div class="page-info"><!----><!----><!----><!----><span class="page-reading-time-info" aria-label="Reading Time"><svg 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177.093z"></path></svg><span>About 2 min</span><meta property="timeRequired" content="PT2M"></span><!----><!----></div><hr></div><div class="toc-place-holder"><aside id="toc"><!--[--><!----><!--]--><div class="toc-header">On This Page<button class="print-button" title="Print"><svg xmlns="http://www.w3.org/2000/svg" class="icon print-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="print icon"><path d="M819.2 364.8h-44.8V128c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v236.8h-44.8C145.067 364.8 96 413.867 96 473.6v192c0 59.733 49.067 108.8 108.8 108.8h44.8V896c0 17.067 14.933 32 32 32h460.8c17.067 0 32-14.933 32-32V774.4h44.8c59.733 0 108.8-49.067 108.8-108.8v-192c0-59.733-49.067-108.8-108.8-108.8zM313.6 160h396.8v204.8H313.6V160zm396.8 704H313.6V620.8h396.8V864zM864 665.6c0 25.6-19.2 44.8-44.8 44.8h-44.8V588.8c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v121.6h-44.8c-25.6 0-44.8-19.2-44.8-44.8v-192c0-25.6 19.2-44.8 44.8-44.8h614.4c25.6 0 44.8 19.2 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| --><h1 id="instructions" tabindex="-1"><a class="header-anchor" href="#instructions" aria-hidden="true">#</a> Instructions</h1><p>The trigger provides a mechanism for listening to changes in time series data. With user-defined logic, tasks such as alerting and data forwarding can be conducted.</p><p>The trigger is implemented based on the reflection mechanism. Users can monitor data changes by implementing the Java interfaces. IoTDB allows users to dynamically register and drop triggers without restarting the server.</p><p>The document will help you learn to define and manage triggers.</p><h2 id="pattern-for-listening" tabindex="-1"><a class="header-anchor" href="#pattern-for-listening" aria-hidden="true">#</a> Pattern for listening</h2><p>A single trigger can be used to listen for data changes in a time series that match a specific pattern. For example, a trigger can listen for the data changes of time series <code>root.sg.a</code>, or time series that match the pattern <code>root.sg.*</code>. When you register a trigger, you can specify the path pattern that the trigger listens on through an SQL statement.</p><h2 id="trigger-type" tabindex="-1"><a class="header-anchor" href="#trigger-type" aria-hidden="true">#</a> Trigger Type</h2><p>There are currently two types of triggers, and you can specify the type through an SQL statement when registering a trigger:</p><ul><li>Stateful triggers: The execution logic of this type of trigger may depend on data from multiple insertion statement . The framework will aggregate the data written by different nodes into the same trigger instance for calculation to retain context information. This type of trigger is usually used for sampling or statistical data aggregation for a period of time. information. Only one node in the cluster holds an instance of a stateful trigger.</li><li>Stateless triggers: The execution logic of the trigger is only related to the current input data. The framework does not need to aggregate the data of different nodes into the same trigger instance. This type of trigger is usually used for calculation of single row data and abnormal detection. Each node in the cluster holds an instance of a stateless trigger.</li></ul><h2 id="trigger-event" tabindex="-1"><a class="header-anchor" href="#trigger-event" aria-hidden="true">#</a> Trigger Event</h2><p>There are currently two trigger events for the trigger, and other trigger events will be expanded in the future. When you register a trigger, you can specify the trigger event through an SQL statement:</p><ul><li>BEFORE INSERT: Fires before the data is persisted. <strong>Please note that currently the trigger does not support data cleaning and will not change the data to be persisted itself.</strong></li><li>AFTER INSERT: Fires after the data is persisted.</li></ul></div><!----><footer class="page-meta"><div class="meta-item edit-link"><a href="https://github.com/apache/iotdb/edit/rel/1.2/docs/UserGuide/Trigger/Instructions.md" rel="noopener noreferrer" target="_blank" aria-label="Found Error? 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