[GitHub] [beam] ibzib commented on a change in pull request #15267: [BEAM-12153] Implement GroupByKey with CombinePerKey with Concatenate CombineFn

[GitBox <gi...@apache.org>]

ibzib commented on a change in pull request #15267:
URL: https://github.com/apache/beam/pull/15267#discussion_r683039093



##########
File path: runners/spark/src/main/java/org/apache/beam/runners/spark/structuredstreaming/translation/batch/GroupByKeyTranslatorBatch.java
##########
@@ -17,74 +17,143 @@
  */
 package org.apache.beam.runners.spark.structuredstreaming.translation.batch;
 
-import java.io.Serializable;
-import org.apache.beam.runners.core.InMemoryStateInternals;
-import org.apache.beam.runners.core.StateInternals;
-import org.apache.beam.runners.core.StateInternalsFactory;
-import org.apache.beam.runners.core.SystemReduceFn;
-import org.apache.beam.runners.spark.structuredstreaming.translation.AbstractTranslationContext;
+import java.util.ArrayList;
+import java.util.List;
 import org.apache.beam.runners.spark.structuredstreaming.translation.TransformTranslator;
-import org.apache.beam.runners.spark.structuredstreaming.translation.batch.functions.GroupAlsoByWindowViaOutputBufferFn;
+import org.apache.beam.runners.spark.structuredstreaming.translation.AbstractTranslationContext;
 import org.apache.beam.runners.spark.structuredstreaming.translation.helpers.EncoderHelpers;
 import org.apache.beam.runners.spark.structuredstreaming.translation.helpers.KVHelpers;
+import org.apache.beam.sdk.coders.CannotProvideCoderException;
 import org.apache.beam.sdk.coders.Coder;
-import org.apache.beam.sdk.coders.IterableCoder;
+import org.apache.beam.sdk.coders.CoderRegistry;
 import org.apache.beam.sdk.coders.KvCoder;
+import org.apache.beam.sdk.coders.ListCoder;
+import org.apache.beam.sdk.transforms.Combine;
+import org.apache.beam.sdk.transforms.GroupByKey;
 import org.apache.beam.sdk.transforms.PTransform;
+import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
 import org.apache.beam.sdk.util.WindowedValue;
 import org.apache.beam.sdk.values.KV;
 import org.apache.beam.sdk.values.PCollection;
 import org.apache.beam.sdk.values.WindowingStrategy;
+import org.apache.spark.api.java.function.FlatMapFunction;
 import org.apache.spark.sql.Dataset;
 import org.apache.spark.sql.KeyValueGroupedDataset;
+import scala.Tuple2;
 
 class GroupByKeyTranslatorBatch<K, V>
-    implements TransformTranslator<
-        PTransform<PCollection<KV<K, V>>, PCollection<KV<K, Iterable<V>>>>> {
+  implements TransformTranslator<
+  PTransform<PCollection<KV<K, V>>, PCollection<KV<K, Iterable<V>>>>> {
+  /**
+   * Combiner that combines {@code T}s into a single {@code List<T>} containing all inputs.
+   *
+   * <p>For internal use to translate {@link GroupByKey}. For a large {@link PCollection} this is
+   * expected to crash!
+   *
+   * <p>This is copied from the dataflow runner code.

Review comment:
       It looks like there are already several implementations of this function. We should define it in a common place so we can reuse it. Possibly in the runner libraries, though it looks like Python even defines the equivalent function publicly: https://beam.apache.org/releases/pydoc/2.31.0/apache_beam.transforms.combiners.html#apache_beam.transforms.combiners.ToList




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