AlexanderSaydakov commented on a change in pull request #5712: HllSketch module URL: https://github.com/apache/incubator-druid/pull/5712#discussion_r218172538
########## File path: extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchMergeBufferAggregator.java ########## @@ -0,0 +1,132 @@ +/* + * 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.nio.ByteBuffer; +import java.util.concurrent.locks.Lock; +import java.util.concurrent.locks.ReadWriteLock; + +import com.google.common.util.concurrent.Striped; +import com.yahoo.memory.WritableMemory; +import com.yahoo.sketches.hll.HllSketch; +import com.yahoo.sketches.hll.TgtHllType; +import com.yahoo.sketches.hll.Union; + +import org.apache.druid.query.aggregation.BufferAggregator; +import org.apache.druid.segment.ColumnValueSelector; + +/** + * This aggregator merges existing sketches. + * The input column must contain {@link HllSketch} + * @author Alexander Saydakov + */ +public class HllSketchMergeBufferAggregator implements BufferAggregator +{ + + private static final int NUM_STRIPES = 64; // for locking per buffer position (power of 2 to make index computation faster) + + 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); + + public HllSketchMergeBufferAggregator( + final ColumnValueSelector<HllSketch> selector, + final int lgK, + final TgtHllType tgtHllType, + final int size + ) + { + this.selector = selector; + this.lgK = lgK; + this.tgtHllType = tgtHllType; + this.size = size; + } + + @Override + public void init(final ByteBuffer buf, final int position) + { + final WritableMemory mem = WritableMemory.wrap(buf).writableRegion(position, size); + new Union(lgK, mem); Review comment: In a sense. We are given a slot in a buffer, and we need to initialize an aggregation object there. Our sketches have a special mode for this (so called "direct" as opposed to "heap"). In this case the Union constructor is given a chunk of memory to occupy. It will initialize a few things there so that later this chunk can be "wrapped" (quickly interpreted as a Union object) and updated: Union union = Union.writableWrap(mem); union.update(sketch); In this mode it is not necessary to keep the constructed object around because it is cheap to reconstruct from the chunk of memory using the "wrapping" operation. Perhaps I should add a comment in the code to explain this. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@druid.apache.org For additional commands, e-mail: commits-h...@druid.apache.org
