AlexanderSaydakov commented on a change in pull request #5712: HllSketch module URL: https://github.com/apache/incubator-druid/pull/5712#discussion_r218163526
########## File path: extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchBuildBufferAggregator.java ########## @@ -0,0 +1,173 @@ +/* + * 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.IdentityHashMap; +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 org.apache.druid.query.aggregation.BufferAggregator; +import org.apache.druid.segment.ColumnValueSelector; +import it.unimi.dsi.fastutil.ints.Int2ObjectMap; +import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap; + +/** + * This aggregator builds sketches from raw data. + * The input column can contain identifiers of type string, char[], byte[] or any numeric type. + * @author Alexander Saydakov + */ +public class HllSketchBuildBufferAggregator 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<Object> selector; + private final int lgK; + private final TgtHllType tgtHllType; + private final int size; + private final IdentityHashMap<ByteBuffer, WritableMemory> memCache = new IdentityHashMap<>(); + private final IdentityHashMap<ByteBuffer, Int2ObjectMap<HllSketch>> sketchCache = new IdentityHashMap<>(); + private final Striped<ReadWriteLock> stripedLock = Striped.readWriteLock(NUM_STRIPES); + + public HllSketchBuildBufferAggregator( + final ColumnValueSelector<Object> 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 = getMemory(buf).writableRegion(position, size); + putSketchIntoCache(buf, position, new HllSketch(lgK, tgtHllType, mem)); + } + + /* + * This method uses locks because it can be used during indexing, + * and Druid can call aggregate() and get() concurrently + * See https://github.com/druid-io/druid/pull/3956 + */ + @Override + public void aggregate(final ByteBuffer buf, final int position) + { + final Object value = selector.getObject(); + if (value == null) { + return; + } + final Lock lock = stripedLock.getAt(lockIndex(position)).writeLock(); + lock.lock(); + try { + final HllSketch sketch = sketchCache.get(buf).get(position); + HllSketchBuildAggregator.updateSketch(sketch, value); + } + finally { + lock.unlock(); + } + } + + /* + * This method uses locks because it can be used during indexing, + * and Druid can call aggregate() and get() concurrently + * See https://github.com/druid-io/druid/pull/3956 + */ + @Override + public Object get(final ByteBuffer buf, final int position) + { + final Lock lock = stripedLock.getAt(lockIndex(position)).readLock(); + lock.lock(); + try { + return sketchCache.get(buf).get(position); + } + finally { + lock.unlock(); + } + } + + @Override + public void close() + { + memCache.clear(); + sketchCache.clear(); + } + + @Override + public float getFloat(final ByteBuffer buf, final int position) + { + throw new UnsupportedOperationException("Not implemented"); + } + + @Override + public long getLong(final ByteBuffer buf, final int position) + { + throw new UnsupportedOperationException("Not implemented"); + } + + private WritableMemory getMemory(final ByteBuffer buf) + { + return memCache.computeIfAbsent(buf, b -> WritableMemory.wrap(b)); + } + + // In very rare cases sketches can exceed given memory, request on-heap memory and move there. 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