# [−][src]Crate exponential_decay_histogram

A histogram which exponentially weights in favor of recent values.

Histograms compute statistics about the distribution of values in a data set. This histogram exponentially favors recent values over older ones, making it suitable for use cases such as monitoring the state of long running processes.

The histogram does not store all values simultaneously, but rather a randomized subset. This allows us to put bounds on overall memory use regardless of the rate of events.

This implementation is based on the `ExponentiallyDecayingReservoir` class in the Java Metrics library, which is itself based on the forward decay model described in Cormode et al. 2009.

# Examples

```use exponential_decay_histogram::ExponentialDecayHistogram;

let mut histogram = ExponentialDecayHistogram::new();

// Do some work for a while and fill the histogram with some information.
// Even though we're putting 10000 values into the histogram, it will only
// retain a subset of them.
for _ in 0..10000 {
let size = do_work();
histogram.update(size);
}

// Take a snapshot to inspect the current state of the histogram.
let snapshot = histogram.snapshot();
println!("count: {}", snapshot.count());
println!("min: {}", snapshot.min());
println!("max: {}", snapshot.max());
println!("mean: {}", snapshot.mean());
println!("standard deviation: {}", snapshot.stddev());
println!("median: {}", snapshot.value(0.5));
println!("99th percentile: {}", snapshot.value(0.99));```

## Structs

 ExponentialDecayHistogram A histogram which exponentially weights in favor of recent values. Snapshot A snapshot of the state of an `ExponentialDecayHistogram` at some point in time. Values An iterator over the distinct values in a snapshot along with their weights.