| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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. |
| */ |
| package org.apache.beam.sdk.io.gcp.datastore; |
| |
| import java.util.Random; |
| import org.apache.beam.sdk.transforms.Sum; |
| import org.apache.beam.sdk.util.MovingFunction; |
| import org.apache.beam.vendor.guava.v20_0.com.google.common.annotations.VisibleForTesting; |
| |
| /** |
| * An implementation of client-side adaptive throttling. See |
| * https://landing.google.com/sre/book/chapters/handling-overload.html#client-side-throttling-a7sYUg |
| * for a full discussion of the use case and algorithm applied. |
| */ |
| class AdaptiveThrottler { |
| private final MovingFunction successfulRequests; |
| private final MovingFunction allRequests; |
| |
| /** |
| * The target ratio between requests sent and successful requests. This is "K" in the formula in |
| * https://landing.google.com/sre/book/chapters/handling-overload.html |
| */ |
| private final double overloadRatio; |
| |
| /** |
| * The target minimum number of requests per samplePeriodMs, even if no requests succeed. Must be |
| * greater than 0, else we could throttle to zero. Because every decision is probabilistic, there |
| * is no guarantee that the request rate in any given interval will not be zero. (This is the +1 |
| * from the formula in https://landing.google.com/sre/book/chapters/handling-overload.html |
| */ |
| private static final double MIN_REQUESTS = 1; |
| |
| private final Random random; |
| |
| /** |
| * @param samplePeriodMs the time window to keep of request history to inform throttling |
| * decisions. |
| * @param sampleUpdateMs the length of buckets within this time window. |
| * @param overloadRatio the target ratio between requests sent and successful requests. You should |
| * always set this to more than 1, otherwise the client would never try to send more requests |
| * than succeeded in the past - so it could never recover from temporary setbacks. |
| */ |
| public AdaptiveThrottler(long samplePeriodMs, long sampleUpdateMs, double overloadRatio) { |
| this(samplePeriodMs, sampleUpdateMs, overloadRatio, new Random()); |
| } |
| |
| @VisibleForTesting |
| AdaptiveThrottler(long samplePeriodMs, long sampleUpdateMs, double overloadRatio, Random random) { |
| allRequests = |
| new MovingFunction( |
| samplePeriodMs, |
| sampleUpdateMs, |
| 1 /* numSignificantBuckets */, |
| 1 /* numSignificantSamples */, |
| Sum.ofLongs()); |
| successfulRequests = |
| new MovingFunction( |
| samplePeriodMs, |
| sampleUpdateMs, |
| 1 /* numSignificantBuckets */, |
| 1 /* numSignificantSamples */, |
| Sum.ofLongs()); |
| this.overloadRatio = overloadRatio; |
| this.random = random; |
| } |
| |
| @VisibleForTesting |
| double throttlingProbability(long nowMsSinceEpoch) { |
| if (!allRequests.isSignificant()) { |
| return 0; |
| } |
| long allRequestsNow = allRequests.get(nowMsSinceEpoch); |
| long successfulRequestsNow = successfulRequests.get(nowMsSinceEpoch); |
| return Math.max( |
| 0, |
| (allRequestsNow - overloadRatio * successfulRequestsNow) / (allRequestsNow + MIN_REQUESTS)); |
| } |
| |
| /** |
| * Call this before sending a request to the remote service; if this returns true, drop the |
| * request (treating it as a failure or trying it again at a later time). |
| */ |
| public boolean throttleRequest(long nowMsSinceEpoch) { |
| double delayProbability = throttlingProbability(nowMsSinceEpoch); |
| // Note that we increment the count of all requests here, even if we return true - so even if we |
| // tell the client not to send a request at all, it still counts as a failed request. |
| allRequests.add(nowMsSinceEpoch, 1); |
| |
| return (random.nextDouble() < delayProbability); |
| } |
| |
| /** Call this after {@link throttleRequest} if your request was successful. */ |
| public void successfulRequest(long nowMsSinceEpoch) { |
| successfulRequests.add(nowMsSinceEpoch, 1); |
| } |
| } |