capistrant commented on code in PR #18136: URL: https://github.com/apache/druid/pull/18136#discussion_r2183799388
########## 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: Is it the same? This is the line I'm most worried about in your patch: `return this.serverSelectorStrategy.pick(query, preferred, segment, numServersToPick);` That is after you have potentially put non-preferred nodes into a list with preferred nodes. The serverSelector strategy does not care about anything other than either picking a random node or the node with the least conns. Secondarily it also adds nodes with differing priorites to that list. So even within the preferred nodes only, isn't it giving the server selector the chance do the wrong priority strategy? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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