capistrant commented on code in PR #18136: URL: https://github.com/apache/druid/pull/18136#discussion_r2178186767
########## server/src/main/java/org/apache/druid/client/selector/PreferredTierSelectorStrategy.java: ########## @@ -0,0 +1,110 @@ +/* + * 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.druid.client.selector; + + +import com.fasterxml.jackson.annotation.JacksonInject; +import it.unimi.dsi.fastutil.ints.Int2ObjectRBTreeMap; +import org.apache.druid.client.QueryableDruidServer; +import org.apache.druid.java.util.common.IAE; +import org.apache.druid.java.util.common.logger.Logger; +import org.apache.druid.query.Query; +import org.apache.druid.timeline.DataSegment; + +import java.util.ArrayList; +import java.util.Comparator; +import java.util.List; +import java.util.Set; + +public class PreferredTierSelectorStrategy extends AbstractTierSelectorStrategy +{ + private static final Logger log = new Logger(PreferredTierSelectorStrategy.class); + + private final String preferredTier; + private final TierSelectorStrategy priorityStrategy; + + public PreferredTierSelectorStrategy( + @JacksonInject ServerSelectorStrategy serverSelectorStrategy, + @JacksonInject PreferredTierSelectorStrategyConfig config + ) + { + super(serverSelectorStrategy); + this.preferredTier = config.getTier(); + + if (config.getPriority() == null) { + this.priorityStrategy = new HighestPriorityTierSelectorStrategy(serverSelectorStrategy); + } else { + if ("highest".equalsIgnoreCase(config.getPriority())) { + this.priorityStrategy = new HighestPriorityTierSelectorStrategy(serverSelectorStrategy); + } else if ("lowest".equalsIgnoreCase(config.getPriority())) { + this.priorityStrategy = new LowestPriorityTierSelectorStrategy(serverSelectorStrategy); + } else { + throw new IAE("druid.broker.select.tier.preferred.priority must be either 'highest' or 'lowest'"); + } + } + } + + @Override + public Comparator<Integer> getComparator() + { + return priorityStrategy.getComparator(); + } + + @Override + public <T> List<QueryableDruidServer> pick( + Query<T> query, + Int2ObjectRBTreeMap<Set<QueryableDruidServer>> prioritizedServers, + DataSegment segment, + int numServersToPick + ) + { + if (log.isDebugEnabled()) { + log.debug( + "Picking [%d] servers from preferred tier [%s] for segment [%s] with priority [%s]", + numServersToPick, preferredTier, segment.getId(), this.priorityStrategy.getClass().getSimpleName() + ); + } + + List<QueryableDruidServer> preferred = new ArrayList<>(numServersToPick); + List<QueryableDruidServer> nonPreferred = new ArrayList<>(numServersToPick); + for (Set<QueryableDruidServer> priorityServers : prioritizedServers.values()) { + for (QueryableDruidServer server : priorityServers) { + if (preferredTier.equals(server.getServer().getMetadata().getTier())) { + preferred.add(server); + if (preferred.size() == numServersToPick) { + return this.serverSelectorStrategy.pick(query, preferred, segment, numServersToPick); + } + } else { + // We have to iterate through all servers even the numbers of the non-preferred servers reach the limit + // This is because we don't know whether there're preferred servers left in the next priority set + nonPreferred.add(server); + } + } + } + + // Fill with non-preferred servers if we don't have enough preferred servers + int fillSize = numServersToPick - preferred.size(); + for (int i = 0; i < fillSize && i < nonPreferred.size(); i++) { + preferred.add(nonPreferred.get(i)); + } + + return this.serverSelectorStrategy.pick(query, preferred, segment, numServersToPick); + } Review Comment: Upon further review, I don't think that this is working as you designed. When I check out your changes on my local and run tests in loop, I get lots of failures. I think the best approach here is to split all of the incoming servers into two Int2ObjectMaps that are sorted by priority. One of them contains all of the preferred servers. The other, the non-preferred servers. You then delegate to the underlying priority selector to do the actual pick for you from the preferred first, and then the non-preferred second (if necessary). I have a potential implementation below in suggestion. I'm not saying this is how it needs to be, but I couldn't think of how to explain what I was thinking in a way that is more clear since it is a little bit goofy side effect of this change would be to revert the ServerSelectorStrategy back to using Set instead of less restrictive Collection, since we no longer call it with lists when delegating pick to the priority strategy. ```suggestion @Override public <T> List<QueryableDruidServer> pick( Query<T> query, Int2ObjectRBTreeMap<Set<QueryableDruidServer>> prioritizedServers, DataSegment segment, int numServersToPick ) { if (log.isDebugEnabled()) { log.debug( "Picking [%d] servers from preferred tier [%s] for segment [%s] with priority [%s]", numServersToPick, preferredTier, segment.getId(), this.priorityStrategy.getClass().getSimpleName() ); } int numPreferredServers = 0; Int2ObjectRBTreeMap<Set<QueryableDruidServer>> preferred = new Int2ObjectRBTreeMap<>(priorityStrategy.getComparator()); Int2ObjectRBTreeMap<Set<QueryableDruidServer>> nonPreferred = new Int2ObjectRBTreeMap<>(priorityStrategy.getComparator()); for (Set<QueryableDruidServer> priorityServers : prioritizedServers.values()) { if (numPreferredServers == numServersToPick) { // We have enough preferred servers to satisfy the request, no need to check further break; } for (QueryableDruidServer server : priorityServers) { if (preferredTier.equals(server.getServer().getMetadata().getTier())) { numPreferredServers++; preferred.computeIfAbsent( server.getServer().getPriority(), p -> new HashSet<>() ); preferred.get(server.getServer().getPriority()).add(server); if (numPreferredServers == numServersToPick) { // We have enough preferred servers to satisfy the request, no need to check further break; } } else { // We have to iterate through all servers even the numbers of the non-preferred servers reach the limit // This is because we don't know whether there are preferred servers left in the next priority set nonPreferred.computeIfAbsent( server.getServer().getPriority(), p -> new HashSet<>() ); nonPreferred.get(server.getServer().getPriority()).add(server); } } } List<QueryableDruidServer> picks = new ArrayList<>(numServersToPick); if (numPreferredServers > 0) { // If we have preferred servers, pick them first picks.addAll(priorityStrategy.pick(query, preferred, segment, numServersToPick)); } if (picks.size() < numServersToPick) { // If we don't have enough preferred servers, pick from the non-preferred ones int remaining = numServersToPick - picks.size(); picks.addAll(priorityStrategy.pick(query, nonPreferred, segment, remaining)); } return picks; } ``` -- This is an automated message from the Apache Git Service. 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