Package io.github.resilience4j.core.metrics

Class SlidingTimeWindowMetrics

java.lang.Object
io.github.resilience4j.core.metrics.SlidingTimeWindowMetrics
All Implemented Interfaces:
Metrics
public class SlidingTimeWindowMetrics extends Object implements Metrics
A Metrics implementation is backed by a sliding time window that aggregates only the calls made in the last N seconds.

The sliding time window is implemented with a circular array of N partial aggregations (buckets). If the time window size is 10 seconds, the circular array has always 10 partial aggregations (buckets). Every bucket aggregates the outcome of all calls which happen in a certain epoch second. (Partial aggregation) The head bucket of the circular array stores the call outcomes of the current epoch second. The other partial aggregations store the call outcomes of the previous N-1 epoch seconds.

The sliding window does not store call outcomes (tuples) individually, but incrementally updates partial aggregations (bucket) and a total aggregation. The total aggregation is updated incrementally when a new call outcome is recorded. When the oldest bucket is evicted, the partial total aggregation of that bucket is subtracted from the total aggregation. (Subtract-on-Evict)

The time to retrieve a Snapshot is constant 0(1), since the Snapshot is pre-aggregated and is independent of the time window size. The space requirement (memory consumption) of this implementation should be nearly constant O(n), since the call outcomes (tuples) are not stored individually. Only N partial aggregations and 1 total aggregation are created.

  • Field Details

    • partialAggregations

      final PartialAggregation[] partialAggregations

    • timeWindowSizeInSeconds

      private final int timeWindowSizeInSeconds

    • totalAggregation

      private final TotalAggregation totalAggregation

    • clock

      private final Clock clock

    • headIndex

      int headIndex

  • Constructor Details

    • SlidingTimeWindowMetrics

      public SlidingTimeWindowMetrics(int timeWindowSizeInSeconds, Clock clock)
      Creates a new SlidingTimeWindowMetrics with the given clock and window of time.
      Parameters:
      timeWindowSizeInSeconds - the window time size in seconds
      clock - the Clock to use

  • Method Details

    • record

      public Snapshot record(long duration, TimeUnit durationUnit, Metrics.Outcome outcome)
      Description copied from interface: Metrics
      Records a call.
      Specified by:
      record in interface Metrics
      Parameters:
      duration - the duration of the call
      durationUnit - the time unit of the duration
      outcome - the outcome of the call

    • getSnapshot

      public Snapshot getSnapshot()
      Description copied from interface: Metrics
      Returns a snapshot.
      Specified by:
      getSnapshot in interface Metrics
      Returns:
      a snapshot

    • moveWindowToCurrentEpochSecond

      private PartialAggregation moveWindowToCurrentEpochSecond(PartialAggregation latestPartialAggregation)
      Moves the end of the time window to the current epoch second. The latest bucket of the circular array is used to calculate how many seconds the window must be moved. The difference is calculated by subtracting the epoch second from the latest bucket from the current epoch second. If the difference is greater than the time window size, the time window size is used.
      Parameters:
      latestPartialAggregation - the latest partial aggregation of the circular array

    • getLatestPartialAggregation

      private PartialAggregation getLatestPartialAggregation()
      Returns the head partial aggregation of the circular array.
      Returns:
      the head partial aggregation of the circular array

    • moveHeadIndexByOne

      void moveHeadIndexByOne()
      Moves the headIndex to the next bucket.