[GitHub] [druid] maytasm commented on a change in pull request #9733: Introduce CompositeQueryLaningStrategy

[GitBox <gi...@apache.org>]

maytasm commented on a change in pull request #9733:
URL: https://github.com/apache/druid/pull/9733#discussion_r412638192



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File path: server/src/main/java/org/apache/druid/server/scheduling/CompositeQueryLaningStrategy.java
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@@ -0,0 +1,85 @@
+/*
+ * 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.server.scheduling;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.google.common.base.Preconditions;
+import it.unimi.dsi.fastutil.objects.Object2IntArrayMap;
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import org.apache.druid.client.SegmentServerSelector;
+import org.apache.druid.query.QueryContexts;
+import org.apache.druid.query.QueryPlus;
+import org.apache.druid.server.QueryLaningStrategy;
+
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+/**
+ * A laning strategy that allows you to combine multiple {@link QueryLaningStrategy}. To use this strategy,
+ * an admin must configure lane groups and their associated strategy.
+ *
+ * For example:
+ * druid.query.scheduler.laning.strategy=composite
+ * druid.query.scheduler.laning.strategies={"manualLanes": {"strategy":"manual", "lanes":{"one": 1}},"hiLoLanes": {"strategy":"hilo", "maxLowPercent":1}}
+ *
+ * This strategy does *not* support nesting a composite strategy within this strategy.
+ */
+public class CompositeQueryLaningStrategy implements QueryLaningStrategy
+{
+  @JsonProperty
+  private final Map<String, QueryLaningStrategy> strategies;
+
+  @JsonCreator
+  public CompositeQueryLaningStrategy(@JsonProperty("strategies") Map<String, QueryLaningStrategy> strategies)
+  {
+    this.strategies = Preconditions.checkNotNull(strategies, "strategies must be set.");
+    Preconditions.checkArgument(!strategies.isEmpty(), "strategies must define at least one strategy.");
+    Preconditions.checkArgument(
+        strategies.values().stream().noneMatch(s -> s instanceof CompositeQueryLaningStrategy),
+        "strategies can not contain a composite strategy."
+    );
+  }
+
+  @Override
+  public Object2IntMap<String> getLaneLimits(int totalLimit)
+  {
+    Object2IntArrayMap<String> laneLimits = new Object2IntArrayMap<>();
+    for (QueryLaningStrategy strategy : strategies.values()) {
+      laneLimits.putAll(strategy.getLaneLimits(totalLimit));
+    }
+    return laneLimits;
+  }
+
+  @Override
+  public <T> Optional<String> computeLane(QueryPlus<T> query, Set<SegmentServerSelector> segments)
+  {
+    String laneStrategyKey = QueryContexts.getCompositeLaneStrategy(query.getQuery());

Review comment:
       Maybe COMPOSITE_LANE_STRATEGY_KEY can be optional in the Query. If it is present, you can find the exact query strategy from the `strategies`. Otherwise (COMPOSITE_LANE_STRATEGY_KEY is not present), you can go through the list in order and call `computeLane` as @clintropolis suggested. I see both cases being useful. (exact strategy key for more control and easy to understand behavior in integration testing  and going through list applying for more pratical use case) 




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