[GitHub] gianm commented on a change in pull request #5712: HllSketch module

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

gianm commented on a change in pull request #5712: HllSketch module
URL: https://github.com/apache/incubator-druid/pull/5712#discussion_r218149008
 
 

 ##########
 File path: extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchAggregatorFactory.java
 ##########
 @@ -0,0 +1,232 @@
+/*
+ * 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.query.aggregation.datasketches.hll;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Objects;
+
+import javax.annotation.Nullable;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.yahoo.sketches.hll.HllSketch;
+import com.yahoo.sketches.hll.TgtHllType;
+import com.yahoo.sketches.hll.Union;
+
+import org.apache.druid.java.util.common.IAE;
+import org.apache.druid.query.aggregation.AggregateCombiner;
+import org.apache.druid.query.aggregation.AggregatorFactory;
+import org.apache.druid.query.aggregation.ObjectAggregateCombiner;
+import org.apache.druid.query.cache.CacheKeyBuilder;
+import org.apache.druid.segment.ColumnValueSelector;
+
+/**
+ * Base class for both build and merge factories
+ * @author Alexander Saydakov
+ */
+abstract class HllSketchAggregatorFactory extends AggregatorFactory
+{
+
+  static final int DEFAULT_LG_K = 12;
+  static final TgtHllType DEFAULT_TGT_HLL_TYPE = TgtHllType.HLL_4;
+
+  static final Comparator<HllSketch> COMPARATOR = Comparator.nullsFirst(Comparator.comparingDouble(HllSketch::getEstimate));
+
+  private final String name;
+  private final String fieldName;
+  private final int lgK;
+  private final TgtHllType tgtHllType;
+
+  HllSketchAggregatorFactory(final String name, final String fieldName, @Nullable final Integer lgK, @Nullable final String tgtHllType)
+  {
+    if (name == null) {
 
 Review comment:
   I think this line is fine the way it is. We don't have a codebase-wide rule about how to handle this stuff, and the way @AlexanderSaydakov did it is within bounds of reasonableness.
   
   (Fwiw, I think if we had a codebase-wide rule for this, it should be geared towards what provides the nicest error messages for users. There are plenty of locations where error messages could be improved.)

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