[GitHub] [beam] iemejia commented on a change in pull request #11065: [BEAM-2939, BEAM-9458] Add deduplication transform

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iemejia commented on a change in pull request #11065: [BEAM-2939, BEAM-9458] Add deduplication transform
URL: https://github.com/apache/beam/pull/11065#discussion_r389407728
 
 

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 File path: sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Deduplicate.java
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+/*
+ * 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.transforms;
+
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.coders.BooleanCoder;
+import org.apache.beam.sdk.coders.Coder;
+import org.apache.beam.sdk.coders.KvCoder;
+import org.apache.beam.sdk.state.StateSpec;
+import org.apache.beam.sdk.state.StateSpecs;
+import org.apache.beam.sdk.state.TimeDomain;
+import org.apache.beam.sdk.state.Timer;
+import org.apache.beam.sdk.state.TimerSpec;
+import org.apache.beam.sdk.state.TimerSpecs;
+import org.apache.beam.sdk.state.ValueState;
+import org.apache.beam.sdk.values.KV;
+import org.apache.beam.sdk.values.PCollection;
+import org.apache.beam.sdk.values.TypeDescriptor;
+import org.joda.time.Duration;
+
+/**
+ * A set of {@link PTransform}s which deduplicate input records over a time domain and threshold.
+ * Values in different windows will not be considered duplicates of each other. Deduplication is
+ * best effort.
+ *
+ * <p>Two values of type {@code T} are compared for equality <b>not</b> by regular Java {@link
+ * Object#equals}, but instead by first encoding each of the elements using the {@code
+ * PCollection}'s {@code Coder}, and then comparing the encoded bytes. This admits efficient
+ * parallel evaluation.
+ *
+ * <p>These PTransforms are different then {@link Distinct} since {@link Distinct} guarantees
+ * uniqueness of values within a {@link PCollection} but may support a narrower set of {@link
+ * org.apache.beam.sdk.values.WindowingStrategy windowing strategies} or may delay when output is
+ * produced.
+ *
+ * <p>The durations specified may impose memory and/or storage requirements within a runner and care
+ * might need to be used to ensure that the deduplication time limit is long enough to remove
+ * duplicates but short enough to not cause performance problems within a runner. Each runner may
+ * provide an optimized implementation of their choice using the deduplication time domain and
+ * threshold specified.
+ *
+ * <p>Does not preserve any order the input PCollection might have had.
+ *
+ * <p>Example of use:
+ *
+ * <pre>{@code
+ * PCollection<String> words = ...;
+ * PCollection<String> deduplicatedWords =
+ *     words.apply(Deduplicate.<String>values());
+ * }</pre>
+ */
+public final class Deduplicate {
 
 Review comment:
   @lukecwik Maybe we should mark this one as `@Experimental` for the moment specially since it is coming directly to core.

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