adarshsanjeev commented on code in PR #15049: URL: https://github.com/apache/druid/pull/15049#discussion_r1400171972
########## docs/development/extensions-contrib/ddsketch-quantiles.md: ########## @@ -0,0 +1,111 @@ +--- +id: ddsketch-quantiles +title: "DDSketches for Approximate Quantiles module" +--- + +<!-- + ~ 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. + --> + + +This module provides aggregators for approximate quantile queries using the [DDSketch](https://github.com/datadog/sketches-java) library. The DDSketch library provides a fast, and fully-mergeable quantile sketch with relative error. If the true quantile is 100, a sketch with relative error of 1% guarantees a quantile value between 101 and 99. This is important and highly valuable behavior for long tail distributions. + +To use this Apache Druid extension, [include](../../configuration/extensions.md#loading-extensions) in the extensions load list. + Review Comment: ```suggestion druid.extensions.loadList=["druid-ddsketch", ...] ``` The name of the extension could be added ########## extensions-contrib/ddsketch/src/main/java/org/apache/druid/query/aggregation/ddsketch/DDSketchObjectStrategy.java: ########## @@ -0,0 +1,73 @@ +/* + * 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.ddsketch; + +import com.datadoghq.sketch.ddsketch.DDSketch; +import com.datadoghq.sketch.ddsketch.DDSketchProtoBinding; +import com.datadoghq.sketch.ddsketch.store.CollapsingLowestDenseStore; +import com.google.protobuf.InvalidProtocolBufferException; +import org.apache.druid.segment.data.ObjectStrategy; + +import javax.annotation.Nullable; +import java.nio.ByteBuffer; + +public class DDSketchObjectStrategy implements ObjectStrategy<DDSketch> +{ + private static final byte[] EMPTY_BYTES = new byte[0]; + + @Override + public Class<DDSketch> getClazz() + { + return DDSketch.class; + } + + @Override + public DDSketch fromByteBuffer(ByteBuffer buffer, int numBytes) + { + if (numBytes == 0) { + return null; + } + ByteBuffer readOnlyBuffer = buffer.asReadOnlyBuffer(); + readOnlyBuffer.limit(buffer.position() + numBytes); + try { + com.datadoghq.sketch.ddsketch.proto.DDSketch proto = com.datadoghq.sketch.ddsketch.proto.DDSketch.parseFrom(readOnlyBuffer); + DDSketch recovered = DDSketchProtoBinding.fromProto(() -> new CollapsingLowestDenseStore(1000), proto); + return recovered; + } + catch (InvalidProtocolBufferException e) { + throw new UnsupportedOperationException("Unable to decode from Proto"); + } + } + + @Override + public byte[] toBytes(@Nullable DDSketch val) + { + if (val == null) { Review Comment: Should the sketch serialize to a null on an empty sketch as well? It would save a bit of time serde (though I'm not sure how much time it would save), and help while merging sketches. I believe this is how quantile sketch extension as well. -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
