BoundarySampler (Brave 5.17.0 API)

java.lang.Object
- brave.sampler.Sampler
- - brave.sampler.BoundarySampler

```
public final class BoundarySampler
extends Sampler
```
This sampler is appropriate for high-traffic instrumentation (ex edge web servers that each receive >100K requests) who provision random trace ids, and make the sampling decision only once. It defends against nodes in the cluster selecting exactly the same ids.
Implementation

This uses modulo 10000 arithmetic, which allows a minimum probability of 0.01%. Trace id collision was noticed in practice in the Twitter front-end cluster. A random salt is here to defend against nodes in the same cluster sampling exactly the same subset of trace ids. The goal was full 64-bit coverage of trace IDs on multi-host deployments.
Based on https://github.com/twitter/finagle/blob/b6b1d0414fa24ed0c8bb5112985a4e9c9bcd3c9e/finagle-zipkin-core/src/main/scala/com/twitter/finagle/zipkin/core/Sampler.scala#L68

Field Summary
- Fields inherited from class brave.sampler.Sampler
  ALWAYS_SAMPLE, NEVER_SAMPLE

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`static Sampler`	`create(float probability)`
`boolean`	`isSampled(long traceId)`	Returns true when `abs(traceId) <= boundary`
`String`	`toString()`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Method Detail
  - create
```
public static Sampler create(float probability)
```
    Parameters:
    
    probability - 0 means never sample, 1 means always sample. Otherwise minimum probability is 0.0001, or 0.01% of traces
  - isSampled
```
public boolean isSampled(long traceId)
```
    Returns true when abs(traceId) <= boundary
    
    Specified by:
    
    isSampled in class Sampler
    
    Parameters:
    
    traceId - The trace ID to be decided on, can be ignored
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object