org.apache.htrace

Interface Sampler<T>

All Known Implementing Classes:

AlwaysSampler, CountSampler, NeverSampler, ProbabilitySampler, TrueIfTracingSampler

public interface Sampler<T>

Extremely simple callback to determine the frequency that an action should be performed.

'T' is the object type you require to create a more advanced sampling function. For example if there is some RPC information in a 'Call' object, you might implement Sampler. Then when the RPC is received you can call one of the Trace.java functions that takes the extra 'info' parameter, which will be passed into the next function you implemented.

For the example above, the next(T info) function may look like this

 public boolean next(T info) {
   if (info == null) {
     return false;
   } else if (info.getName().equals("get")) {
     return Math.random() > 0.5;
   } else if (info.getName().equals("put")) {
     return Math.random() > 0.25;
   } else {
     return false;
   }
 }
 
 

This would trace 50% of all gets, 75% of all puts and would not trace any other requests.

Field Summary

Fields

Modifier and Type	Field and Description
static Sampler<?>	ALWAYS
static Sampler<?>	NEVER

Method Summary

Methods

Modifier and Type	Method and Description
boolean	next(T info)

Field Detail

ALWAYS

static final Sampler<?> ALWAYS

NEVER

static final Sampler<?> NEVER

Method Detail

next

boolean next(T info)