36 lines
7.7 KiB
HTML
36 lines
7.7 KiB
HTML
<html><head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
|
<title>4. 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-sleuth.html" title="Spring Cloud Sleuth"><link rel="up" href="multi_spring-cloud-sleuth.html" title="Spring Cloud Sleuth"><link rel="prev" href="multi__features.html" title="3. Features"><link rel="next" href="multi__propagation.html" title="5. Propagation"></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">4. Sampling</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__features.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="multi__propagation.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_sampling" href="#_sampling"></a>4. Sampling</h1></div></div></div><p>Sampling may be employed to reduce the data collected and reported out of process.
|
|
When a span is not sampled, it adds no overhead (a noop).</p><p>Sampling is an up-front decision, meaning that the decision to report data is made at the first operation in a trace and that decision is propagated downstream.</p><p>By default, a global sampler applies a single rate to all traced operations.
|
|
<code class="literal">Tracer.Builder.sampler</code> controls this setting, and it defaults to tracing every request.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_declarative_sampling" href="#_declarative_sampling"></a>4.1 Declarative sampling</h2></div></div></div><p>Some applications need to sample based on the type or annotations of a java method.</p><p>Most users use a framework interceptor to automate this sort of policy.
|
|
The following example shows how that might work internally:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// derives a sample rate from an annotation on a java method</span>
|
|
DeclarativeSampler<Traced> sampler = DeclarativeSampler.create(Traced::sampleRate);
|
|
|
|
<em><span class="hl-annotation" style="color: gray">@Around("@annotation(traced)")</span></em>
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Object traceThing(ProceedingJoinPoint pjp, Traced traced) <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">throws</span> Throwable {
|
|
Span span = tracing.tracer().newTrace(sampler.sample(traced))...
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">try</span> {
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> pjp.proceed();
|
|
} <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">finally</span> {
|
|
span.finish();
|
|
}
|
|
}</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_custom_sampling" href="#_custom_sampling"></a>4.2 Custom sampling</h2></div></div></div><p>Depending on what the operation is, you may want to apply different policies.
|
|
For example, you might not want to trace requests to static resources such as images, or you might want to trace all requests to a new api.</p><p>Most users use a framework interceptor to automate this sort of policy.
|
|
The following example shows how that might work internally:</p><pre class="programlisting">Span newTrace(Request input) {
|
|
SamplingFlags flags = SamplingFlags.NONE;
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (input.url().startsWith(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"/experimental"</span>)) {
|
|
flags = SamplingFlags.SAMPLED;
|
|
} <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">else</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (input.url().startsWith(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"/static"</span>)) {
|
|
flags = SamplingFlags.NOT_SAMPLED;
|
|
}
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> tracer.newTrace(flags);
|
|
}</pre><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 preceding example forms the basis for the built-in <a class="link" href="https://github.com/openzipkin/sleuth/tree/master/instrumentation/http" target="_top">http sampler</a>.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_sampling_in_spring_cloud_sleuth" href="#_sampling_in_spring_cloud_sleuth"></a>4.3 Sampling in Spring Cloud Sleuth</h2></div></div></div><p>By default Spring Cloud Sleuth sets all spans to non-exportable.
|
|
That means that traces appear in logs but not in any remote store.
|
|
For testing the default is often enough, and it probably is all you need if you use only the logs (for example, with an ELK aggregator).
|
|
If you export span data to Zipkin, there is also an <code class="literal">Sampler.ALWAYS_SAMPLE</code> setting that exports everything and a <code class="literal">ProbabilityBasedSampler</code> setting that samples a 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">ProbabilityBasedSampler</code> is the default if you use <code class="literal">spring-cloud-sleuth-zipkin</code>.
|
|
You can configure the exports by setting <code class="literal">spring.sleuth.sampler.probability</code>.
|
|
The passed value needs to be a double from <code class="literal">0.0</code> to <code class="literal">1.0</code>.</p></td></tr></table></div><p>A sampler can be installed by creating a bean definition, as shown in the following example:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Bean</span></em>
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Sampler defaultSampler() {
|
|
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> Sampler.ALWAYS_SAMPLE;
|
|
}</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 set the <code class="literal">spanFlags</code> header to <code class="literal">1</code>.
|
|
Doing so forces the current span to be exportable regardless of the sampling decision.</p></td></tr></table></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__features.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="multi__propagation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">3. Features </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-sleuth.html">Home</a></td><td width="40%" align="right" valign="top"> 5. Propagation</td></tr></table></div></body></html> |