gparai commented on a change in pull request #1715: DRILL-7117: Support creation of equi-depth histogram for selected dat… URL: https://github.com/apache/drill/pull/1715#discussion_r269752998
########## File path: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/statistics/TDigestMergedStatistic.java ########## @@ -0,0 +1,135 @@ +/* + * 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.drill.exec.physical.impl.statistics; + +// Library implementing TDigest algorithm to derive approximate quantiles. Please refer to: +// 'Computing Extremely Accurate Quantiles using t-Digests' by Ted Dunning and Otmar Ertl + +import com.clearspring.analytics.stream.quantile.TDigest; +import org.apache.drill.common.types.TypeProtos; +import org.apache.drill.exec.ExecConstants; +import org.apache.drill.exec.server.options.OptionManager; +import org.apache.drill.exec.vector.NullableVarBinaryVector; +import org.apache.drill.exec.vector.ValueVector; +import org.apache.drill.exec.vector.complex.MapVector; + +import java.util.HashMap; +import java.util.Map; +import java.nio.ByteBuffer; + +public class TDigestMergedStatistic extends AbstractMergedStatistic { + private Map<String, TDigest> tdigestHolder; + private int compression; + + public TDigestMergedStatistic() { + this.tdigestHolder = new HashMap<>(); + state = State.INIT; + } + + @Override + public void initialize(String inputName, double samplePercent) { + super.initialize(Statistic.TDIGEST_MERGE, inputName, samplePercent); + state = State.CONFIG; + } + + @Override + public String getName() { + return name; + } + + @Override + public String getInput() { + return inputName; + } + + @Override + public void merge(MapVector input) { + // Check the input is a Map Vector + assert (input.getField().getType().getMinorType() == TypeProtos.MinorType.MAP); + for (ValueVector vv : input) { + String colName = vv.getField().getName(); + TDigest colTdigestHolder = null; + if (tdigestHolder.get(colName) != null) { + colTdigestHolder = tdigestHolder.get(colName); + } + NullableVarBinaryVector tdigestVector = (NullableVarBinaryVector) vv; + NullableVarBinaryVector.Accessor accessor = tdigestVector.getAccessor(); + + try { + if (!accessor.isNull(0)) { + TDigest other = TDigest.fromBytes(ByteBuffer.wrap(accessor.get(0))); + if (colTdigestHolder != null) { + colTdigestHolder.add(other); + tdigestHolder.put(colName, colTdigestHolder); + } else { + tdigestHolder.put(colName, other); + } + } + } catch (Exception ex) { + //TODO: Catch IOException/CardinalityMergeException + //TODO: logger + } + } + } + + public TDigest getStat(String colName) { + if (state != State.COMPLETE) { + throw new IllegalStateException(String.format("Statistic `%s` has not completed merging statistics", + name)); + } + return tdigestHolder.get(colName); + } + + @Override + public void setOutput(MapVector output) { + // Check the input is a Map Vector + assert (output.getField().getType().getMinorType() == TypeProtos.MinorType.MAP); + // Dependencies have been configured correctly + assert (state == State.MERGE); + for (ValueVector outMapCol : output) { + String colName = outMapCol.getField().getName(); + TDigest colTdigestHolder = tdigestHolder.get(colName); + NullableVarBinaryVector vv = (NullableVarBinaryVector) outMapCol; + vv.allocateNewSafe(); + try { + if (colTdigestHolder != null) { + int size = colTdigestHolder.smallByteSize(); + java.nio.ByteBuffer byteBuf = java.nio.ByteBuffer.allocate(size); + colTdigestHolder.asSmallBytes(byteBuf); + // NOTE: in setting the VV below, we are using the byte[] instead of the ByteBuffer because the + // latter was producing incorrect output (after re-reading the data from the VV). It is + // unclear whether the setSafe() api for ByteBuffer has a bug, so to be safe we are using the + // byte[] directly which works. + vv.getMutator().setSafe(0, byteBuf.array(), 0, byteBuf.array().length); Review comment: Sampling will throw off the histogram values just like NDV. Do we plan to address it now or later? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to 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
