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26 lines
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<title>49. Sampling</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="multi_spring-cloud.html" title="Spring Cloud"><link rel="up" href="multi__spring_cloud_sleuth.html" title="Part VII. Spring Cloud Sleuth"><link rel="prev" href="multi__features_2.html" title="48. Features"><link rel="next" href="multi__instrumentation.html" title="50. Instrumentation"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">49. Sampling</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__features_2.html">Prev</a> </td><th width="60%" align="center">Part VII. Spring Cloud Sleuth</th><td width="20%" align="right"> <a accesskey="n" href="multi__instrumentation.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_sampling" href="#_sampling"></a>49. Sampling</h2></div></div></div><p>In distributed tracing the data volumes can be very high so sampling
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can be important (you usually don’t need to export all spans to get a
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good picture of what is happening). Spring Cloud Sleuth has a
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<code class="literal">Sampler</code> strategy that you can implement to take control of the
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sampling algorithm. Samplers do not stop span (correlation) ids from
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being generated, but they do prevent the tags and events being
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attached and exported. By default you get a strategy that continues to
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trace if a span is already active, but new ones are always marked as
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non-exportable. If all your apps run with this sampler you will see
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traces in logs, but not in any remote store. For testing the default
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is often enough, and it probably is all you need if you are only using
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the logs (e.g. with an ELK aggregator). If you are exporting span data
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to Zipkin or Spring Cloud Stream, there is also an <code class="literal">AlwaysSampler</code>
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that exports everything and a <code class="literal">PercentageBasedSampler</code> that samples a
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fixed fraction of spans.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>the <code class="literal">PercentageBasedSampler</code> is the default if you are using
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<code class="literal">spring-cloud-sleuth-zipkin</code> or <code class="literal">spring-cloud-sleuth-stream</code>. You can
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configure the exports using <code class="literal">spring.sleuth.sampler.percentage</code>. The passed
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value needs to be a double from <code class="literal">0.0</code> to <code class="literal">1.0</code> so it’s not a percentage.
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For backwards compatibility reasons we’re not changing the property name.</p></td></tr></table></div><p>A sampler can be installed just by creating a bean definition, e.g:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Bean</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Sampler defaultSampler() {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> AlwaysSampler();
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}</pre><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left">Tip</th></tr><tr><td align="left" valign="top"><p>You can set the HTTP header <code class="literal">X-B3-Flags</code> to <code class="literal">1</code> or when doing messaging you can
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set <code class="literal">spanFlags</code> header to <code class="literal">1</code>. Then the current span will be forced to be exportable
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regardless of the sampling decision.</p></td></tr></table></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__features_2.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="multi__spring_cloud_sleuth.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="multi__instrumentation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">48. Features </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud.html">Home</a></td><td width="40%" align="right" valign="top"> 50. Instrumentation</td></tr></table></div></body></html> |