[GitHub] [incubator-druid] gianm commented on a change in pull request #8194: HllSketch Merge/Build BufferAggregators: Speed up init with prebuilt sketch.

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

gianm commented on a change in pull request #8194: HllSketch Merge/Build BufferAggregators: Speed up init with prebuilt sketch.
URL: https://github.com/apache/incubator-druid/pull/8194#discussion_r308890340
 
 

 ##########
 File path: extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchMergeBufferAggregator.java
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 @@ -40,14 +40,17 @@
 public class HllSketchMergeBufferAggregator implements BufferAggregator
 {
 
-  /** for locking per buffer position (power of 2 to make index computation faster) */
+  /**
+   * for locking per buffer position (power of 2 to make index computation faster)
+   */
   private static final int NUM_STRIPES = 64;
 
   private final ColumnValueSelector<HllSketch> selector;
   private final int lgK;
   private final TgtHllType tgtHllType;
   private final int size;
   private final Striped<ReadWriteLock> stripedLock = Striped.readWriteLock(NUM_STRIPES);
+  private final byte[] emptySketch;
 
 Review comment:
   Renamed it.

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