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https://issues.apache.org/jira/browse/BEAM-7013?focusedWorklogId=295533&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-295533
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ASF GitHub Bot logged work on BEAM-7013:
----------------------------------------
Author: ASF GitHub Bot
Created on: 15/Aug/19 16:33
Start Date: 15/Aug/19 16:33
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_r314284036
##########
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>. The {@code HllCount PTransform}s provided here produce and
consume sketches
+ * compatible with BigQuery.
+ *
+ * <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.forLongs().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.forBytes().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.forStrings().globally()).apply(HllCount.Extract.globally());
+ * }</pre>
+ *
+ * Note: Currently HllCount does not work on FnAPI workers. See <a
+ * href="https://issues.apache.org/jira/browse/BEAM-7879";>Jira ticket
[BEAM-7879]</a>.
+ */
+@Experimental
+public final class HllCount {
+
+ /**
+ * The minimum {@code precision} value you can set in {@link
Init.Builder#withPrecision(int)} is
+ * {@value}.
+ */
+ public static final int MINIMUM_PRECISION =
HyperLogLogPlusPlus.MINIMUM_PRECISION;
+
+ /**
+ * The maximum {@code precision} value you can set in {@link
Init.Builder#withPrecision(int)} is
+ * {@value}.
+ */
+ public static final int MAXIMUM_PRECISION =
HyperLogLogPlusPlus.MAXIMUM_PRECISION;
+
+ /**
+ * The default {@code precision} value used in {@link
Init.Builder#withPrecision(int)} is
+ * {@value}.
+ */
+ public static final int DEFAULT_PRECISION =
HyperLogLogPlusPlus.DEFAULT_NORMAL_PRECISION;
+
+ // Cannot be instantiated. This class is intended to be a namespace only.
+ private HllCount() {}
+
+ /**
+ * Provide {@code PTransform}s to aggregate inputs into HLL++ sketches. The
four supported input
+ * types are {@code Integer}, {@code Long}, {@code String}, and {@code
byte[]}.
+ *
+ * <p>Sketches are represented using the {@code byte[]} type. Sketches of
the same type and {@code
+ * precision} can be merged into a new sketch using {@link
HllCount.MergePartial}. Estimated count
+ * of distinct elements can be extracted from sketches using {@link
HllCount.Extract}.
+ *
+ * <p>Correspond to the {@code HLL_COUNT.INIT(input [, precision])} function
in <a
+ *
href="https://cloud.google.com/bigquery/docs/reference/standard-sql/hll_functions";>BigQuery</a>.
+ */
+ public static final class Init {
+
+ // Cannot be instantiated. This class is intended to be a namespace only.
+ private Init() {}
+
+ /**
+ * Returns a {@link Builder} for a {@code HllCount.Init} combining {@code
PTransform} that
+ * computes integer-type HLL++ sketches. Call {@link Builder#globally()}
or {@link
+ * Builder#perKey()} on the returning {@link Builder} to finalize the
{@code PTransform}.
+ *
+ * <p>Calling {@link Builder#globally()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<Integer>} and returns a {@code PCollection<byte[]>} whose
contents is the
+ * integer-type HLL++ sketch computed from the elements in the input
{@code PCollection}.
+ *
+ * <p>Calling {@link Builder#perKey()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<KV<K, Integer>>} and returns a {@code PCollection<KV<K,
byte[]>>} whose contents
+ * is the per-key integer-type HLL++ sketch computed from the values
matching each key in the
+ * input {@code PCollection}.
+ *
+ * <p>Integer-type sketches cannot be merged with sketches of other types.
+ */
+ public static Builder<Integer> forIntegers() {
+ return new Builder<>(HllCountInitFn.forInteger());
+ }
+
+ /**
+ * Returns a {@link Builder} for a {@code HllCount.Init} combining {@code
PTransform} that
+ * computes long-type HLL++ sketches. Call {@link Builder#globally()} or
{@link
+ * Builder#perKey()} on the returning {@link Builder} to finalize the
{@code PTransform}.
+ *
+ * <p>Calling {@link Builder#globally()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<Long>} and returns a {@code PCollection<byte[]>} whose
contents is the long-type
+ * HLL++ sketch computed from the elements in the input {@code
PCollection}.
+ *
+ * <p>Calling {@link Builder#perKey()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<KV<K, Long>>} and returns a {@code PCollection<KV<K,
byte[]>>} whose contents is
+ * the per-key long-type HLL++ sketch computed from the values matching
each key in the input
+ * {@code PCollection}.
+ *
+ * <p>Long-type sketches cannot be merged with sketches of other types.
+ */
+ public static Builder<Long> forLongs() {
+ return new Builder<>(HllCountInitFn.forLong());
+ }
+
+ /**
+ * Returns a {@link Builder} for a {@code HllCount.Init} combining {@code
PTransform} that
+ * computes string-type HLL++ sketches. Call {@link Builder#globally()} or
{@link
+ * Builder#perKey()} on the returning {@link Builder} to finalize the
{@code PTransform}.
+ *
+ * <p>Calling {@link Builder#globally()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<String>} and returns a {@code PCollection<byte[]>} whose
contents is the
+ * string-type HLL++ sketch computed from the elements in the input {@code
PCollection}.
+ *
+ * <p>Calling {@link Builder#perKey()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<KV<K, String>>} and returns a {@code PCollection<KV<K,
byte[]>>} whose contents
+ * is the per-key string-type HLL++ sketch computed from the values
matching each key in the
+ * input {@code PCollection}.
+ *
+ * <p>String-type sketches cannot be merged with sketches of other types.
+ */
+ public static Builder<String> forStrings() {
+ return new Builder<>(HllCountInitFn.forString());
+ }
+
+ /**
+ * Returns a {@link Builder} for a {@code HllCount.Init} combining {@code
PTransform} that
+ * computes bytes-type HLL++ sketches. Call {@link Builder#globally()} or
{@link
+ * Builder#perKey()} on the returning {@link Builder} to finalize the
{@code PTransform}.
+ *
+ * <p>Calling {@link Builder#globally()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<byte[]>} and returns a {@code PCollection<byte[]>} whose
contents is the
+ * bytes-type HLL++ sketch computed from the elements in the input {@code
PCollection}.
+ *
+ * <p>Calling {@link Builder#perKey()} returns a {@code PTransform} that
takes an input {@code
+ * PCollection<KV<K, byte[]>>} and returns a {@code PCollection<KV<K,
byte[]>>} whose contents
+ * is the per-key bytes-type HLL++ sketch computed from the values
matching each key in the
+ * input {@code PCollection}.
+ *
+ * <p>Bytes-type sketches cannot be merged with sketches of other types.
+ */
+ public static Builder<byte[]> forBytes() {
+ return new Builder<>(HllCountInitFn.forBytes());
+ }
+
+ /**
+ * Builder for the {@code HllCount.Init} combining {@code PTransform}.
+ *
+ * <p>Call {@link #withPrecision(int)} to customize the {@code precision}
parameter of the
+ * sketch.
+ *
+ * <p>Call {@link #globally()} or {@link #perKey()} to finalize the {@code
PTransform}.
+ *
+ * @param <InputT> element type or value type in {@code KV}s of the input
{@code PCollection} to
+ * the {@code PTransform} being built
+ */
+ public static final class Builder<InputT> {
+
+ private final HllCountInitFn<InputT, ?> initFn;
+
+ private Builder(HllCountInitFn<InputT, ?> initFn) {
+ this.initFn = initFn;
+ }
+
+ /**
+ * Explicitly set the {@code precision} parameter used to compute HLL++
sketch.
+ *
+ * <p>Valid range is between {@link #MINIMUM_PRECISION} and {@link
#MAXIMUM_PRECISION}. If
+ * this method is not called, {@link #DEFAULT_PRECISION} will be used.
Sketches computed using
+ * different {@code precision}s cannot be merged together.
+ *
+ * @param precision the {@code precision} parameter used to compute
HLL++ sketch
+ */
+ public Builder<InputT> withPrecision(int precision) {
+ initFn.setPrecision(precision);
+ return this;
+ }
+
+ /**
+ * Returns a {@link Combine.Globally} {@code PTransform} that takes an
input {@code
+ * PCollection<InputT>} and returns a {@code PCollection<byte[]>} whose
contents is the HLL++
+ * sketch computed from the elements in the input {@code PCollection}.
+ *
+ * <p>Returns an empty output {@code PCollection} if the input {@code
PCollection} is empty.
+ */
+ public Combine.Globally<InputT, byte[]> globally() {
+ return Combine.globally(initFn).withoutDefaults();
+ }
+
+ /**
+ * Returns a {@link Combine.PerKey} {@code PTransform} that takes an
input {@code
+ * PCollection<KV<K, InputT>>} and returns a {@code PCollection<KV<K,
byte[]>>} whose contents
+ * is the per-key HLL++ sketch computed from the values matching each
key in the input {@code
+ * PCollection}.
+ */
+ public <K> Combine.PerKey<K, InputT, byte[]> perKey() {
+ return Combine.perKey(initFn);
+ }
+ }
+ }
+
+ /**
+ * Provide {@code PTransform}s to merge HLL++ sketches into a new sketch.
+ *
+ * <p>Only sketches of the same type and {@code precision} can be merged
together. If incompatible
+ * sketches are provided, a runtime error will occur.
+ *
+ * <p>Correspond to the {@code HLL_COUNT.MERGE_PARTIAL(sketch)} function in
<a
+ *
href="https://cloud.google.com/bigquery/docs/reference/standard-sql/hll_functions";>BigQuery</a>.
+ */
+ public static final class MergePartial {
+
+ // Cannot be instantiated. This class is intended to be a namespace only.
+ private MergePartial() {}
+
+ /**
+ * Returns a {@link Combine.Globally} {@code PTransform} that takes an
input {@code
+ * PCollection<byte[]>} of HLL++ sketches and returns a {@code
PCollection<byte[]>} of a new
+ * sketch merged from the input sketches.
+ *
+ * <p>Only sketches of the same type and {@code precision} can be merged
together. If
Review comment:
True for type; for precision, we can merge sketches of unequal precision;
all sketches just get downgraded to the minimum precision encountered (see
https://github.com/google/zetasketch/blob/master/java/com/google/zetasketch/internal/hllplus/Representation.java
=> merge(..)).
(Same for perKey(..) doc below)
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Issue Time Tracking
-------------------
Worklog Id: (was: 295533)
Time Spent: 18h 20m (was: 18h 10m)
> 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: 18h 20m
> Remaining Estimate: 0h
>
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