[GitHub] [incubator-druid] gianm commented on a change in pull request #8194: HllSketchMergeBufferAggregator: Speed up init by copying prebuilt sketch.

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

gianm commented on a change in pull request #8194: HllSketchMergeBufferAggregator: Speed up init by copying prebuilt sketch.
URL: https://github.com/apache/incubator-druid/pull/8194#discussion_r308851053
 
 

 ##########
 File path: extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchMergeBufferAggregator.java
 ##########
 @@ -60,17 +63,22 @@ public HllSketchMergeBufferAggregator(
     this.lgK = lgK;
     this.tgtHllType = tgtHllType;
     this.size = size;
+    this.emptySketch = new byte[size];
+
+    //noinspection ResultOfObjectAllocationIgnored (Union writes to "emptySketch" as a side effect of construction)
+    new Union(lgK, WritableMemory.wrap(emptySketch, ByteOrder.LITTLE_ENDIAN).writableRegion(0, size));
 
 Review comment:
   Thanks, I removed this.

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