com.netflix.hystrix.util
Class HystrixRollingPercentile

java.lang.Object
  com.netflix.hystrix.util.HystrixRollingPercentile

public class HystrixRollingPercentile
extends java.lang.Object

Add values to a rolling window and retrieve percentile calculations such as median, 90th, 99th, etc.

The underlying data structure contains a circular array of buckets that "roll" over time.

For example, if the time window is configured to 60 seconds with 12 buckets of 5 seconds each, values will be captured in each 5 second bucket and rotate each 5 seconds.

This means that percentile calculations are for the "rolling window" of 55-60 seconds up to 5 seconds ago.

Each bucket will contain a circular array of long values and if more than the configured amount (1000 values for example) it will wrap around and overwrite values until time passes and a new bucket is allocated. This sampling approach for high volume metrics is done to conserve memory and reduce sorting time when calculating percentiles.

Constructor Summary

HystrixRollingPercentile(HystrixProperty<java.lang.Integer> timeInMilliseconds, HystrixProperty<java.lang.Integer> numberOfBuckets, HystrixProperty<java.lang.Integer> bucketDataLength)

Method Summary

void	addValue(int... value) Add value (or values) to current bucket.
int	getMean() This returns the mean (average) of all values in the current snapshot.
int	getPercentile(double percentile) Compute a percentile from the underlying rolling buckets of values.
void	reset() Force a reset so that percentiles start being gathered from scratch.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HystrixRollingPercentile

public HystrixRollingPercentile(HystrixProperty<java.lang.Integer> timeInMilliseconds,
                                HystrixProperty<java.lang.Integer> numberOfBuckets,
                                HystrixProperty<java.lang.Integer> bucketDataLength)

Parameters:

timeInMilliseconds - HystrixProperty<Integer> for nummber of milliseconds of data that should be tracked

Example: 60000 for 1 minute

numberOfBuckets - HystrixProperty<Integer> for number of buckets that the time window should be divided into

Example: 12 for 5 second buckets in a 1 minute window

bucketDataLength - HystrixProperty<Integer> for number of values stored in each bucket

Example: 1000 to store a max of 1000 values in each 5 second bucket

Method Detail

addValue

public void addValue(int... value)

Add value (or values) to current bucket.

Parameters:

value - Value to be stored in current bucket such as execution latency in milliseconds

getPercentile

public int getPercentile(double percentile)

Compute a percentile from the underlying rolling buckets of values.

For performance reasons it maintains a single snapshot of the sorted values from all buckets that is re-generated each time the bucket rotates.

This means that if a bucket is 5000ms, then this method will re-compute a percentile at most once every 5000ms.

Parameters:

percentile - value such as 99 (99th percentile), 99.5 (99.5th percentile), 50 (median, 50th percentile) to compute and retrieve percentile from rolling buckets.

Returns:

int percentile value

getMean

public int getMean()

This returns the mean (average) of all values in the current snapshot. This is not a percentile but often desired so captured and exposed here.

Returns:

mean of all values

reset

public void reset()

Force a reset so that percentiles start being gathered from scratch.