// @flow
// Copyright (c) 2016 Uber Technologies, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under the License
// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
// or implied. See the License for the specific language governing permissions and limitations under
// the License.
import * as constants from '../constants.js';
import ProbabilisticSampler from './probabilistic_sampler.js';
import RateLimitingSampler from './ratelimiting_sampler.js';
// GuaranteedThroughputProbabilisticSampler is a sampler that leverages both probabilisticSampler and
// rateLimitingSampler. The rateLimitingSampler is used as a guaranteed lower bound sampler such that
// every operation is sampled at least once in a time interval defined by the lowerBound. ie a lowerBound
// of 1.0 / (60 * 10) will sample an operation at least once every 10 minutes.
//
// The probabilisticSampler is given higher priority when tags are emitted, ie. if IsSampled() for both
// samplers return true, the tags for probabilisticSampler will be used.
export default class GuaranteedThroughputSampler {
_probabilisticSampler: ProbabilisticSampler;
_lowerBoundSampler: RateLimitingSampler;
_tagsPlaceholder: any;
constructor(lowerBound: number, samplingRate: number) {
this._probabilisticSampler = new ProbabilisticSampler(samplingRate);
this._lowerBoundSampler = new RateLimitingSampler(lowerBound);
// we never let the lowerBoundSampler return its real tags, so avoid allocations
// by reusing the same placeholder object
this._tagsPlaceholder = {};
}
name(): string {
return 'GuaranteedThroughputSampler';
}
toString(): string {
return `${this.name()}(samplingRate=${this._probabilisticSampler.samplingRate}, lowerBound=${
this._lowerBoundSampler.maxTracesPerSecond
})`;
}
isSampled(operation: string, tags: any): boolean {
if (this._probabilisticSampler.isSampled(operation, tags)) {
// make rate limiting sampler update its budget
this._lowerBoundSampler.isSampled(operation, this._tagsPlaceholder);
return true;
}
let decision = this._lowerBoundSampler.isSampled(operation, this._tagsPlaceholder);
if (decision) {
tags[constants.SAMPLER_TYPE_TAG_KEY] = constants.SAMPLER_TYPE_LOWER_BOUND;
tags[constants.SAMPLER_PARAM_TAG_KEY] = this._probabilisticSampler.samplingRate;
}
return decision;
}
equal(other: Sampler): boolean {
if (!(other instanceof GuaranteedThroughputSampler)) {
return false;
}
return (
this._probabilisticSampler.equal(other._probabilisticSampler) &&
this._lowerBoundSampler.equal(other._lowerBoundSampler)
);
}
close(callback: ?Function): void {
// neither probabilistic nor rate limiting samplers allocate resources,
// so their close methods are effectively no-op. We do not need to
// pass the callback to them (if we did we'd need to wrap it).
this._probabilisticSampler.close(() => {});
this._lowerBoundSampler.close(() => {});
if (callback) {
callback();
}
}
update(lowerBound: number, samplingRate: number): boolean {
let updated = false;
if (this._probabilisticSampler.samplingRate != samplingRate) {
this._probabilisticSampler = new ProbabilisticSampler(samplingRate);
updated = true;
}
if (this._lowerBoundSampler.maxTracesPerSecond != lowerBound) {
updated = this._lowerBoundSampler.update(lowerBound);
}
return updated;
}
}
|