LatencyTracker (apache-nutch 1.22 API)

java.lang.Object
- org.apache.nutch.metrics.LatencyTracker

```
public class LatencyTracker
extends Object
```
A utility class for tracking latency metrics using TDigest for percentile calculation.
This class wraps a TDigest data structure to collect latency samples and emit Hadoop counters with count, sum, and percentile values (p50, p95, p99).
Usage:
```
 // In mapper/reducer setup
 latencyTracker = new LatencyTracker(NutchMetrics.GROUP_FETCHER, NutchMetrics.FETCHER_LATENCY);
 
 // During processing
 long start = System.currentTimeMillis();
 // ... operation ...
 latencyTracker.record(System.currentTimeMillis() - start);
 
 // In cleanup
 latencyTracker.emitCounters(context);
 
```
Emits the following counters:
- {prefix}_count_total - total number of samples
- {prefix}_sum_ms - sum of all latencies in milliseconds
- {prefix}_p50_ms - 50th percentile (median) latency
- {prefix}_p95_ms - 95th percentile latency
- {prefix}_p99_ms - 99th percentile latency
Since:

1.22

Constructor Summary

Constructors
Constructor Description

LatencyTracker(String group, String prefix)
Creates a new LatencyTracker.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`emitCounters(TaskInputOutputContext<?,?,?,?> context)`	Emits all latency counters to the Hadoop context.
`long`	`getCount()`	Returns the number of recorded samples.
`long`	`getPercentile(double quantile)`	Returns the percentile value for the given quantile.
`long`	`getSum()`	Returns the sum of all recorded latencies.
`void`	`record(long latencyMs)`	Records a latency sample.

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

- Constructor Detail
  - LatencyTracker
```
public LatencyTracker(String group,
                      String prefix)
```
    Creates a new LatencyTracker.
    
    Parameters:
    
    group - the Hadoop counter group name
    
    prefix - the prefix for counter names (e.g., "fetch_latency")
- Method Detail
  - record
```
public void record(long latencyMs)
```
    Records a latency sample.
    
    Parameters:
    
    latencyMs - the latency in milliseconds
  - getCount
```
public long getCount()
```
    Returns the number of recorded samples.
    
    Returns:
    
    the count of recorded latency samples
  - getSum
```
public long getSum()
```
    Returns the sum of all recorded latencies.
    
    Returns:
    
    the sum of latencies in milliseconds
  - getPercentile
```
public long getPercentile(double quantile)
```
    Returns the percentile value for the given quantile.
    
    Parameters:
    
    quantile - the quantile (0.0 to 1.0)
    
    Returns:
    
    the percentile value in milliseconds
  - emitCounters
```
public void emitCounters(TaskInputOutputContext<?,?,?,?> context)
```
    Emits all latency counters to the Hadoop context.
    Should be called once during cleanup to emit aggregated metrics.
    
    Parameters:
    
    context - the Hadoop task context