<section>
 <h1 class="contains-headerlink leafygreen-ui-41fr9s" weight="medium">
  cursor.tailable()
  <a class="headerlink leafygreen-ui-1kepx47" href="#cursor.tailable--" title="Permalink to this heading">
   <svg aria-label="Link Icon" class="leafygreen-ui-a30zj9" fill="none" height="12" role="img" viewbox="0 0 16 16" width="12" xmlns="http://www.w3.org/2000/svg">
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    </path>
    <path d="M9.961 6.047c.12.12.228.248.327.38l-1.45 1.445a1.553 1.553 0 0 0-2.496-.423l-2.885 2.87a1.57 1.57 0 0 0-.01 2.213 1.553 1.553 0 0 0 2.203.01l.379-.377a.995.995 0 0 1 1.411.006 1.005 1.005 0 0 1-.006 1.418l-.38.377a3.542 3.542 0 0 1-5.024-.023 3.58 3.58 0 0 1 .022-5.047l2.884-2.871a3.542 3.542 0 0 1 5.025.022Z" fill="currentColor">
    </path>
   </svg>
   <div class="css-1btu0w3 evvkmar0" id="cursor.tailable--">
   </div>
  </a>
 </h1>
 <div class="leafygreen-ui-a5yxub">
  <p class="css-1cmx2d4 ef7gu8j0">
   On this page
  </p>
  <ul class="css-1qb0mst ef7gu8j1">
   <li class="leafygreen-ui-1e7a0ei">
    <a class="lg-ui-0001 leafygreen-ui-e98ikf" href="#definition" target="_self">
     <span>
      Definition
     </span>
    </a>
   </li>
   <li class="leafygreen-ui-1jqtqlb">
    <a class="lg-ui-0001 leafygreen-ui-cpmeq5" href="#behavior" target="_self">
     <span>
      Behavior
     </span>
    </a>
   </li>
  </ul>
 </div>
 <section>
  <h2 class="contains-headerlink leafygreen-ui-19f71ei" weight="medium">
   Definition
   <a class="headerlink leafygreen-ui-1kepx47" href="#definition" title="Permalink to this heading">
    <svg aria-label="Link Icon" class="leafygreen-ui-a30zj9" fill="none" height="12" role="img" viewbox="0 0 16 16" width="12" xmlns="http://www.w3.org/2000/svg">
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     </path>
     <path d="M9.961 6.047c.12.12.228.248.327.38l-1.45 1.445a1.553 1.553 0 0 0-2.496-.423l-2.885 2.87a1.57 1.57 0 0 0-.01 2.213 1.553 1.553 0 0 0 2.203.01l.379-.377a.995.995 0 0 1 1.411.006 1.005 1.005 0 0 1-.006 1.418l-.38.377a3.542 3.542 0 0 1-5.024-.023 3.58 3.58 0 0 1 .022-5.047l2.884-2.871a3.542 3.542 0 0 1 5.025.022Z" fill="currentColor">
     </path>
    </svg>
    <div class="css-1btu0w3 evvkmar0" id="definition">
    </div>
   </a>
  </h2>
  <dl class="method">
   <dt>
    <code class="leafygreen-ui-1l06pbn">
     cursor.tailable()
    </code>
    <a class="headerlink leafygreen-ui-1kepx47" href="#mongodb-method-cursor.tailable" title="Permalink to this definition">
     <svg aria-label="Link Icon" class="leafygreen-ui-a30zj9" fill="none" height="12" role="img" viewbox="0 0 16 16" width="12" xmlns="http://www.w3.org/2000/svg">
      <path d="M6.039 9.953a3.596 3.596 0 0 1-.327-.38l1.45-1.445a1.553 1.553 0 0 0 2.496.423l2.885-2.87a1.57 1.57 0 0 0 .01-2.213 1.553 1.553 0 0 0-2.203-.01l-.379.377A.995.995 0 0 1 8.56 3.83a1.005 1.005 0 0 1 .006-1.418l.38-.377a3.542 3.542 0 0 1 5.024.023 3.58 3.58 0 0 1-.022 5.047l-2.884 2.871a3.542 3.542 0 0 1-5.025-.022Z" fill="currentColor">
      </path>
      <path d="M9.961 6.047c.12.12.228.248.327.38l-1.45 1.445a1.553 1.553 0 0 0-2.496-.423l-2.885 2.87a1.57 1.57 0 0 0-.01 2.213 1.553 1.553 0 0 0 2.203.01l.379-.377a.995.995 0 0 1 1.411.006 1.005 1.005 0 0 1-.006 1.418l-.38.377a3.542 3.542 0 0 1-5.024-.023 3.58 3.58 0 0 1 .022-5.047l2.884-2.871a3.542 3.542 0 0 1 5.025.022Z" fill="currentColor">
      </path>
     </svg>
     <div class="css-1btu0w3 evvkmar0" id="mongodb-method-cursor.tailable">
     </div>
    </a>
   </dt>
   <dd>
    <div class="leafygreen-ui-85da11" role="note">
     <h2 class="leafygreen-ui-1ac4g5h">
      Important
     </h2>
     <h3 class="leafygreen-ui-144d5kf">
      <strong>
       mongosh Method
      </strong>
     </h3>
     <div class="leafygreen-ui-9mycqc">
      <p class="leafygreen-ui-1kp3ins">
       This page documents a
       <a class="lg-ui-0001 leafygreen-ui-fgcsv5" href="https://www.mongodb.com/docs/mongodb-shell/#mongodb-binary-bin.mongosh" target="_self">
        <span>
         <code class="leafygreen-ui-1l06pbn">
          mongosh
         </code>
        </span>
       </a>
       method. This is
       <em>
        not
       </em>
       the documentation for a language-specific driver, such as Node.js.
      </p>
      <p class="leafygreen-ui-1kp3ins">
       For MongoDB API drivers, refer to the language-specific
       <a class="lg-ui-0001 leafygreen-ui-fgcsv5" href="https://www.mongodb.com/docs/drivers/" target="_self">
        <span>
         MongoDB driver documentation
         <!-- -->
         .
        </span>
       </a>
      </p>
     </div>
    </div>
    <p class="leafygreen-ui-1kp3ins">
     Marks the cursor as
     <a class="leafygreen-ui-tqgtui" href="/docs/manual/core/tailable-cursors/#std-label-tailable-cursors-landing-page">
      tailable
     </a>
     keeping it open even when the client exhausts all results.
    </p>
    <p class="leafygreen-ui-1kp3ins">
     For use against a
     <a class="leafygreen-ui-tqgtui" href="/docs/manual/core/capped-collections/#std-label-manual-capped-collection">
      capped collection
     </a>
     only. Using
     <code class="leafygreen-ui-1l06pbn">
      ~cursor.tailable()
     </code>
     against a non-capped collection returns
an error.
    </p>
    <p class="leafygreen-ui-1kp3ins">
     <a class="lg-ui-0001 leafygreen-ui-fgcsv5" href="#mongodb-method-cursor.tailable" target="_self">
      <span>
       <code class="leafygreen-ui-1l06pbn">
        cursor.tailable()
       </code>
      </span>
     </a>
     uses the following syntax:
    </p>
    <script class="structured_data" type="application/ld+json">
     {"@context":"https://schema.org","@type":"SoftwareSourceCode","codeSampleType":"code snippet","text":"cursor.tailable( { awaitData : &lt;boolean&gt; } )","programmingLanguage":"JavaScript"}
    </script>
    <div class="css-16lmvu9">
     <div class="leafygreen-ui-196mwvg">
      <div class="leafygreen-ui-yzcs8i">
       <pre class="leafygreen-ui-1q4bxgx" tabindex="-1"><code class="lg-highlight-hljs-light javascript leafygreen-ui-9ybzas"><table class="leafygreen-ui-1tr4g10"><tbody><tr class=""><td class="leafygreen-ui-7razhx">cursor.<span class="lg-highlight-title lg-highlight-function">tailable</span>( <!-- -->{ <!-- -->awaitData <!-- -->: &lt;<!-- -->boolean<!-- -->&gt; <!-- -->} )</td></tr></tbody></table></code></pre>
       <div class="leafygreen-ui-1bqcprk" data-testid="leafygreen-code-panel">
        <button aria-disabled="false" aria-label="Copy" class="leafygreen-ui-1c6zwke" data-testid="code_copy-button" tabindex="0">
         <div class="leafygreen-ui-xhlipt">
          <svg aria-label="Copy Icon" class="leafygreen-ui-1st74h4" height="16" role="img" viewbox="0 0 16 16" width="16">
           <path clip-rule="evenodd" d="M1 5.71428V10.2857C1 11.2325 1.76751 12 2.71429 12H5.75V7.10957C5.75 6.54414 5.97724 6.00244 6.38065 5.60623L8.67403 3.35381C8.77447 3.25516 8.88376 3.16757 9 3.09182V2.71429C9 1.76751 8.23249 1 7.28571 1H5.8V4.42857C5.8 5.13865 5.22437 5.71428 4.51429 5.71428H1ZM9 4.78571L7.25654 6.49804C7.24689 6.50752 7.23749 6.5172 7.22834 6.52708C7.22208 6.53383 7.21594 6.54068 7.20991 6.54762C7.07504 6.70295 7 6.90234 7 7.10957V7.79762H9H10.0095C10.4829 7.79762 10.8667 7.41386 10.8667 6.94047V4H10.1505C9.92587 4 9.7102 4.0882 9.54992 4.24562L9 4.78571ZM4.86667 1H4.15053C3.92587 1 3.7102 1.0882 3.54992 1.24562L1.25654 3.49804C1.09244 3.65921 1 3.87957 1 4.10957V4.79762H4.00952C4.48291 4.79762 4.86667 4.41386 4.86667 3.94047V1ZM7 12V8.71428H9H10.5143C11.2244 8.71428 11.8 8.13865 11.8 7.42857V4H13.2857C14.2325 4 15 4.76751 15 5.71429V13.2857C15 14.2325 14.2325 15 13.2857 15H8.71429C7.76751 15 7 14.2325 7 13.2857V12Z" fill="currentColor" fill-rule="evenodd">
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       </div>
      </div>
     </div>
    </div>
    <p class="leafygreen-ui-1kp3ins">
     <code class="leafygreen-ui-1l06pbn">
      ~cursor.tailable()
     </code>
     has the following parameter:
    </p>
    <div class="leafygreen-ui-skkc39" tabindex="0">
     <table class="leafygreen-ui-hr8lsv">
      <colgroup>
       <col style="width:20%"/>
       <col style="width:20%"/>
       <col style="width:80%"/>
      </colgroup>
      <thead class="leafygreen-ui-a9ho40">
       <tr data-testid="leafygreen-ui-header-row">
        <th class="leafygreen-ui-1trtg6r" role="columnheader" scope="col">
         <div class="leafygreen-ui-ui0te9">
          <div>
           Parameter
          </div>
         </div>
        </th>
        <th class="leafygreen-ui-13uteka" role="columnheader" scope="col">
         <div class="leafygreen-ui-ui0te9">
          <div>
           Type
          </div>
         </div>
        </th>
        <th class="leafygreen-ui-13uteka" role="columnheader" scope="col">
         <div class="leafygreen-ui-ui0te9">
          <div>
           Description
          </div>
         </div>
        </th>
       </tr>
      </thead>
      <tbody>
       <tr class="">
        <td class="leafygreen-ui-1drjk7h">
         <div class="leafygreen-ui-1n4j8xf">
          <div>
           <code class="leafygreen-ui-1l06pbn">
            awaitData
           </code>
          </div>
         </div>
        </td>
        <td class="leafygreen-ui-1drjk7h">
         <div class="leafygreen-ui-1n4j8xf">
          <div>
           boolean
          </div>
         </div>
        </td>
        <td class="leafygreen-ui-1drjk7h">
         <div class="leafygreen-ui-1n4j8xf">
          <div>
           <p class="leafygreen-ui-1kp3ins">
            Optional. For use with
            <a class="leafygreen-ui-tqgtui" href="/docs/manual/reference/method/cursor.addOption/#mongodb-data-DBQuery.Option.tailable">
             <code class="leafygreen-ui-1l06pbn">
              DBQuery.Option.tailable
             </code>
            </a>
            .
Sets the cursor to block the query thread when no data is
available and await data for a set time instead of immediately
returning no data. The cursor returns no data only if the
timeout expires.
           </p>
           <p class="leafygreen-ui-1kp3ins">
            By default, if
            <code class="leafygreen-ui-1l06pbn">
             maxTimeMS
            </code>
            is set on the command that
created the cursor, then the timeout for
            <code class="leafygreen-ui-1l06pbn">
             awaitData
            </code>
            is the
remaining time. Otherwise, the default timeout is 1000
milliseconds.
           </p>
           <p class="leafygreen-ui-1kp3ins">
            You can set a timeout when running
            <a class="leafygreen-ui-tqgtui" href="/docs/manual/reference/command/getMore/#mongodb-dbcommand-dbcmd.getMore">
             <code class="leafygreen-ui-1l06pbn">
              getMore
             </code>
            </a>
            on a
cursor with
            <code class="leafygreen-ui-1l06pbn">
             awaitData
            </code>
            enabled.
           </p>
           <p class="leafygreen-ui-1kp3ins">
            Defaults to
            <code class="leafygreen-ui-1l06pbn">
             false
            </code>
            .
           </p>
          </div>
         </div>
        </td>
       </tr>
      </tbody>
     </table>
    </div>
    <table class="css-11h39yh e1nex8bq0">
     <colgroup>
      <col class="field-name"/>
      <col class="field-body"/>
     </colgroup>
     <tbody>
      <tr class="css-x8snli">
       <th>
        Returns
        <!-- -->
        :
       </th>
       <td>
        The
        <a class="leafygreen-ui-tqgtui" href="/docs/manual/reference/glossary/#std-term-cursor">
         cursor
        </a>
        that
        <code class="leafygreen-ui-1l06pbn">
         ~cursor.tailable()
        </code>
        is attached to.
       </td>
      </tr>
     </tbody>
    </table>
   </dd>
  </dl>
 </section>
 <section>
  <h2 class="contains-headerlink leafygreen-ui-19f71ei" weight="medium">
   Behavior
   <a class="headerlink leafygreen-ui-1kepx47" href="#behavior" title="Permalink to this heading">
    <svg aria-label="Link Icon" class="leafygreen-ui-a30zj9" fill="none" height="12" role="img" viewbox="0 0 16 16" width="12" xmlns="http://www.w3.org/2000/svg">
     <path d="M6.039 9.953a3.596 3.596 0 0 1-.327-.38l1.45-1.445a1.553 1.553 0 0 0 2.496.423l2.885-2.87a1.57 1.57 0 0 0 .01-2.213 1.553 1.553 0 0 0-2.203-.01l-.379.377A.995.995 0 0 1 8.56 3.83a1.005 1.005 0 0 1 .006-1.418l.38-.377a3.542 3.542 0 0 1 5.024.023 3.58 3.58 0 0 1-.022 5.047l-2.884 2.871a3.542 3.542 0 0 1-5.025-.022Z" fill="currentColor">
     </path>
     <path d="M9.961 6.047c.12.12.228.248.327.38l-1.45 1.445a1.553 1.553 0 0 0-2.496-.423l-2.885 2.87a1.57 1.57 0 0 0-.01 2.213 1.553 1.553 0 0 0 2.203.01l.379-.377a.995.995 0 0 1 1.411.006 1.005 1.005 0 0 1-.006 1.418l-.38.377a3.542 3.542 0 0 1-5.024-.023 3.58 3.58 0 0 1 .022-5.047l2.884-2.871a3.542 3.542 0 0 1 5.025.022Z" fill="currentColor">
     </path>
    </svg>
    <div class="css-1btu0w3 evvkmar0" id="behavior">
    </div>
   </a>
  </h2>
  <p class="leafygreen-ui-1kp3ins">
   A tailable cursor performs a collection scan over a
   <a class="leafygreen-ui-tqgtui" href="/docs/manual/core/capped-collections/#std-label-manual-capped-collection">
    capped collection
   </a>
   .
It remains open even after reaching the end of the collection.
Applications can continue to iterate the tailable cursor as
new data is inserted into the collection.
  </p>
  <p class="leafygreen-ui-1kp3ins">
   If
   <code class="leafygreen-ui-1l06pbn">
    awaitData
   </code>
   is
   <code class="leafygreen-ui-1l06pbn">
    true
   </code>
   , when the cursor reaches the end of
the capped collection,
   <a class="leafygreen-ui-tqgtui" href="/docs/manual/reference/program/mongod/#std-program-mongod">
    <code class="leafygreen-ui-1l06pbn">
     mongod
    </code>
   </a>
   blocks the query thread
for the timeout interval and waits for new data to arrive. When new
data is inserted into the capped collection,
   <code class="leafygreen-ui-1l06pbn">
    mongod
   </code>
   signals the
blocked thread to wake and return the next batch to the client.
  </p>
  <p class="leafygreen-ui-1kp3ins">
   See
   <a class="leafygreen-ui-tqgtui" href="/docs/manual/core/tailable-cursors/#std-label-tailable-cursors-landing-page">
    Tailable Cursors
    <!-- -->
    .
   </a>
  </p>
 </section>
</section>
