[GitHub] [incubator-druid] samarthjain commented on a change in pull request #7331: TDigest backed sketch aggregators

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

samarthjain commented on a change in pull request #7331: TDigest backed sketch aggregators
URL: https://github.com/apache/incubator-druid/pull/7331#discussion_r281958380
 
 

 ##########
 File path: extensions-contrib/tdigestsketch/src/main/java/org/apache/druid/query/aggregation/tdigestsketch/TDigestBuildSketchBufferAggregator.java
 ##########
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+/*
+ * 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.tdigestsketch;
+
+import com.google.common.base.Preconditions;
+import com.tdunning.math.stats.MergingDigest;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
+import org.apache.druid.java.util.common.IAE;
+import org.apache.druid.query.aggregation.BufferAggregator;
+import org.apache.druid.segment.ColumnValueSelector;
+
+import javax.annotation.Nonnull;
+import javax.annotation.concurrent.GuardedBy;
+import java.nio.ByteBuffer;
+import java.util.IdentityHashMap;
+import java.util.Map;
+
+/**
+ * Aggregator that builds t-digest backed sketches using numeric values read from {@link ByteBuffer}
+ */
+public class TDigestBuildSketchBufferAggregator implements BufferAggregator
+{
+
+  @Nonnull
+  private final ColumnValueSelector selector;
+  @Nonnull
+  private final int compression;
+
+  @GuardedBy("this")
+  private Map<ByteBuffer, Int2ObjectMap<MergingDigest>> sketches = new IdentityHashMap<>();
+
+  public TDigestBuildSketchBufferAggregator(
+      final ColumnValueSelector valueSelector,
+      final Integer compression
+  )
+  {
+    Preconditions.checkNotNull(valueSelector);
+    this.selector = valueSelector;
+    if (compression != null) {
+      this.compression = compression;
+    } else {
+      this.compression = TDigestBuildSketchAggregator.DEFAULT_COMPRESSION;
+    }
+  }
+
+  @Override
+  public synchronized void init(ByteBuffer buffer, int position)
 
 Review comment:
   @jihoonson - unfortunately the documentation on the base classes/interfaces doesn't clearly mention which methods could be called in a multi-threaded fashion. So I ended up following what the DataSketches implementation does. 
   For ex - 
   https://github.com/apache/incubator-druid/blob/master/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/quantiles/DoublesSketchBuildBufferAggregator.java#L54
   

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