AlexanderSaydakov 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_r308948043
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File path:
extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchMergeBufferAggregator.java
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@@ -60,17 +69,25 @@ public HllSketchMergeBufferAggregator(
this.lgK = lgK;
this.tgtHllType = tgtHllType;
this.size = size;
+ this.emptyUnion = new byte[size];
+
+ //noinspection ResultOfObjectAllocationIgnored (Union writes to
"emptyUnion" as a side effect of construction)
+ new Union(lgK, WritableMemory.wrap(emptyUnion));
}
- @SuppressWarnings("ResultOfObjectAllocationIgnored")
@Override
public void init(final ByteBuffer buf, final int position)
{
- final WritableMemory mem = WritableMemory.wrap(buf,
ByteOrder.LITTLE_ENDIAN).writableRegion(position, size);
- // Not necessary to keep the constructed object since it is cheap to
reconstruct by wrapping the memory.
- // The objects are not cached as in BuildBufferAggregator since they never
exceed the max size and never move.
Review comment:
Perhaps it is worth keeping this comment explaining why there is no caching
of union objects is done as opposed to cashing of sketches in the
HllSketchBuildBufferAggregator
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