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| <h1>Detecting Slow Consumers</h1> |
| <div id="toc" class="toc2"> |
| <div id="toctitle"><a href="index.html">User Manual for 2.33.0</a></div> |
| <ul class="sectlevel1"> |
| <li><a href="#required-configuration">1. Required Configuration</a></li> |
| <li><a href="#example">2. Example</a></li> |
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| <div id="preamble"> |
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| <p>In this section we will discuss how Apache ActiveMQ Artemis can be configured to deal with slow consumers. |
| A slow consumer with a server-side queue (e.g. JMS topic subscriber) can pose a significant problem for broker performance. |
| If messages build up in the consumer’s server-side queue then memory will begin filling up and the broker may enter paging mode which would impact performance negatively. |
| However, criteria can be set so that consumers which don’t acknowledge messages quickly enough can potentially be disconnected from the broker, which in the case of a non-durable JMS subscriber, would allow the broker to remove the subscription and all of its messages freeing up valuable server resources.</p> |
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| <div class="sect1"> |
| <h2 id="required-configuration"><a class="anchor" href="#required-configuration"></a><a class="link" href="#required-configuration">1. Required Configuration</a></h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>By default the server will not detect slow consumers. |
| If slow consumer detection is desired then see <a href="address-model.html#address-model">address model chapter</a> for more details on the required address settings.</p> |
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| <div class="paragraph"> |
| <p>The calculation to determine whether or not a consumer is slow only inspects the number of messages a particular consumer has <em>acknowledged</em>. |
| It doesn’t take into account whether or not flow control has been enabled on the consumer, whether or not the consumer is streaming a large message, etc. |
| Keep this in mind when configuring slow consumer detection.</p> |
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| <div class="paragraph"> |
| <p>Please note that slow consumer checks are performed using the scheduled thread pool and that each queue on the broker with slow consumer detection enabled will cause a new entry in the internal <code>java.util.concurrent.ScheduledThreadPoolExecutor</code> instance. |
| If there are a high number of queues and the <code>slow-consumer-check-period</code> is relatively low then there may be delays in executing some of the checks. |
| However, this will not impact the accuracy of the calculations used by the detection algorithm. |
| See <a href="thread-pooling.html#thread-management">thread pooling</a> for more details about this pool.</p> |
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| <h2 id="example"><a class="anchor" href="#example"></a><a class="link" href="#example">2. Example</a></h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>See the <a href="examples.html#slow-consumer">slow consumer example</a> which shows how to detect a slow consumer with Apache ActiveMQ Artemis.</p> |
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