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https://issues.apache.org/jira/browse/BEAM-7013?focusedWorklogId=293265&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-293265
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ASF GitHub Bot logged work on BEAM-7013:
----------------------------------------
Author: ASF GitHub Bot
Created on: 12/Aug/19 17:09
Start Date: 12/Aug/19 17:09
Worklog Time Spent: 10m
Work Description: zfraa commented on pull request #9144: [BEAM-7013]
Integrating ZetaSketch's HLL++ algorithm with Beam
URL: https://github.com/apache/beam/pull/9144#discussion_r311447115
##########
File path:
sdks/java/extensions/zetasketch/src/main/java/org/apache/beam/sdk/extensions/zetasketch/HllCount.java
##########
@@ -0,0 +1,364 @@
+/*
+ * 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.beam.sdk.extensions.zetasketch;
+
+import com.google.zetasketch.HyperLogLogPlusPlus;
+import org.apache.beam.sdk.annotations.Experimental;
+import org.apache.beam.sdk.transforms.Combine;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.apache.beam.sdk.transforms.PTransform;
+import org.apache.beam.sdk.transforms.ParDo;
+import org.apache.beam.sdk.values.KV;
+import org.apache.beam.sdk.values.PCollection;
+
+/**
+ * {@code PTransform}s to compute HyperLogLogPlusPlus (HLL++) sketches on data
streams based on the
+ * <a href="https://github.com/google/zetasketch";>ZetaSketch</a>
implementation.
+ *
+ * <p>HLL++ is an algorithm implemented by Google that estimates the count of
distinct elements in a
+ * data stream. HLL++ requires significantly less memory than the linear
memory needed for exact
+ * computation, at the cost of a small error. Cardinalities of arbitrary
breakdowns can be computed
+ * using the HLL++ sketch. See this <a
+ *
href="http://static.googleusercontent.com/media/research.google.com/en/us/pubs/archive/40671.pdf";>published
+ * paper</a> for details about the algorithm.
+ *
+ * <p>HLL++ functions are also supported in <a
+ *
href="https://cloud.google.com/bigquery/docs/reference/standard-sql/hll_functions";>Google
Cloud
+ * BigQuery</a>. Using the {@code HllCount PTransform}s makes the
interoperation with BigQuery
+ * easier.
+ *
+ * <p>For detailed design of this class, see https://s.apache.org/hll-in-beam.
+ *
+ * <h3>Examples</h3>
+ *
+ * <h4>Example 1: Create long-type sketch for a {@code PCollection<Long>} and
specify precision</h4>
+ *
+ * <pre>{@code
+ * PCollection<Long> input = ...;
+ * int p = ...;
+ * PCollection<byte[]> sketch =
input.apply(HllCount.Init.longSketch().withPrecision(p).globally());
+ * }</pre>
+ *
+ * <h4>Example 2: Create bytes-type sketch for a {@code PCollection<KV<String,
byte[]>>}</h4>
+ *
+ * <pre>{@code
+ * PCollection<KV<String, byte[]>> input = ...;
+ * PCollection<KV<String, byte[]>> sketch =
input.apply(HllCount.Init.bytesSketch().perKey());
+ * }</pre>
+ *
+ * <h4>Example 3: Merge existing sketches in a {@code PCollection<byte[]>}
into a new one</h4>
+ *
+ * <pre>{@code
+ * PCollection<byte[]> sketches = ...;
+ * PCollection<byte[]> mergedSketch =
sketches.apply(HllCount.MergePartial.globally());
+ * }</pre>
+ *
+ * <h4>Example 4: Estimates the count of distinct elements in a {@code
PCollection<String>}</h4>
+ *
+ * <pre>{@code
+ * PCollection<String> input = ...;
+ * PCollection<Long> countDistinct =
+ *
input.apply(HllCount.Init.stringSketch().globally()).apply(HllCount.Extract.globally());
Review comment:
Re: stringSketch(), longSketch(), bytesSketch() ...: I wonder whether
"forStrings()", "forLongs(), forBytes()", ... would be easier to read?
"stringSketch" can be misread as "are these sketches going to be stored as
strings? And bytesSketch is a sketch stored as bytes?".
P.S. thanks for this great documentation/examples block, this is working
great as an intro how to use the PTransform!
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Issue Time Tracking
-------------------
Worklog Id: (was: 293265)
> A new count distinct transform based on BigQuery compatible HyperLogLog++
> implementation
> ----------------------------------------------------------------------------------------
>
> Key: BEAM-7013
> URL: https://issues.apache.org/jira/browse/BEAM-7013
> Project: Beam
> Issue Type: New Feature
> Components: extensions-java-sketching, sdk-java-core
> Reporter: Yueyang Qiu
> Assignee: Yueyang Qiu
> Priority: Major
> Fix For: 2.16.0
>
> Time Spent: 12h 20m
> Remaining Estimate: 0h
>
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