qos::percentile

An alternative traffic shaping option to backpressure. Instead of all dropping events for a given time we drop a statistical subset with an increasing percentage of events dropped the longer we see errors / timeouts.

In general step_up should always be significantly smaller then step_down to ensure we gradually reapproach the ideal state.

This operator preserves event metadata.

Configuration options:

• timeout - Maximum allowed 'write' time in nanoseconds.
• step_down - What additional percentile should be dropped in the case of a timeout (default 5%: 0.05)
• step_up - What percentile should be recovered in case of a good event. (default: 0.1%: 0.001)

Outputs:

• out
• overflow - Events that are not let past due to active backpressure

Example:

use std::time::nanos;

define operator perc from qos::percentile
with
  timeout = nanos::from_millis(100),
  step_down = 0.1 # 10%
end;