com.github.rollingmetrics.counter

Class SmoothlyDecayingRollingCounter

java.lang.Object

com.github.rollingmetrics.counter.SmoothlyDecayingRollingCounter

All Implemented Interfaces:

WindowCounter

public class SmoothlyDecayingRollingCounter
extends Object
implements WindowCounter

The rolling time window counter implementation which resets its state by chunks. The unique properties which makes this counter probably the best "rolling time window" implementation are following:

• Sufficient performance about tens of millions concurrent writes and reads per second.
• Predictable and low memory consumption, the memory which consumed by counter does not depend from amount and frequency of writes.
• Perfectly user experience, the continuous observation does not see the sudden changes of sum. This property achieved by smoothly decaying of oldest chunk of counter.

Concurrency properties:

• Writing is lock-free.
• Sum reading is lock-free.

Usage recommendations:

• Only when you need in "rolling time window" semantic.

Performance considerations:

• You can consider writing speed as a constant. The write latency does not depend from count of chunk or frequency of chunk rotation.
• The writing depends only from level of contention between writers(internally counter implemented across AtomicLong).
• The huge count of chunk leads to the slower calculation of their sum. So precision of sum conflicts with latency of sum. You need to choose meaningful values. For example 10 chunks will guarantee at least 90% accuracy and ten million reads per second.

Example of usage:

         // constructs the counter which divided by 10 chunks with 60 seconds time window.
         // one chunk will be reset to zero after each 6 second,
         WindowCounter counter = new SmoothlyDecayingRollingCounter(Duration.ofSeconds(60), 10);
         counter.add(42);
     
 

Constructor Summary

Constructors

Constructor and Description
SmoothlyDecayingRollingCounter(Duration rollingWindow, int numberChunks) Constructs the chunked counter divided by numberChunks.
SmoothlyDecayingRollingCounter(Duration rollingWindow, int numberChunks, Ticker ticker)

Method Summary

Modifier and Type	Method and Description
void	add(long delta) Increment the counter by delta.
int	getChunkCount()
Duration	getRollingWindow()
long	getSum() Returns the counter's current value.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

SmoothlyDecayingRollingCounter

public SmoothlyDecayingRollingCounter(Duration rollingWindow,
                                      int numberChunks)

Constructs the chunked counter divided by numberChunks. The counter will invalidate one chunk each time when rollingWindow/numberChunks millis has elapsed, except oldest chunk which invalidated continuously. The memory consumed by counter and latency of sum calculation depend directly from numberChunks

Example of usage:

         // constructs the counter which divided by 10 chunks with 60 seconds time window.
         // one chunk will be reset to zero after each 6 second,
         WindowCounter counter = new SmoothlyDecayingRollingCounter(Duration.ofSeconds(60), 10);
         counter.add(42);
     
 

Parameters:

rollingWindow - the rolling time window duration

numberChunks - The count of chunk to split counter

SmoothlyDecayingRollingCounter

public SmoothlyDecayingRollingCounter(Duration rollingWindow,
                                      int numberChunks,
                                      Ticker ticker)

Method Detail

getRollingWindow

public Duration getRollingWindow()

Returns:

the rolling window duration for this counter

getChunkCount

public int getChunkCount()

Returns:

the number of chunks

add

public void add(long delta)

Description copied from interface: WindowCounter

Increment the counter by delta. If You want to decrement instead of increment then use negative delta.

Specified by:

add in interface WindowCounter

Parameters:

delta - the amount by which the counter will be increased

getSum

public long getSum()

Description copied from interface: WindowCounter

Returns the counter's current value.

Specified by:

getSum in interface WindowCounter

Returns:

the counter's current value

toString

public String toString()

Overrides:

toString in class Object