lukecwik commented on a change in pull request #10897: [BEAM-2939] Java
UnboundedSource SDF wrapper
URL: https://github.com/apache/beam/pull/10897#discussion_r384868638
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File path: sdks/java/core/src/main/java/org/apache/beam/sdk/io/Read.java
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@@ -375,4 +422,361 @@ public void checkDone() throws IllegalStateException {
}
}
}
+
+ /**
+ * A splittable {@link DoFn} which executes an {@link UnboundedSource}.
+ *
+ * <p>We model the element as the original source and the restriction as a
pair of the sub-source
+ * and its {@link CheckpointMark}. This allows us to split the sub-source
over and over as long as
+ * the checkpoint mark is {@code null} or the {@link NoopCheckpointMark}
since it does not
+ * maintain any state.
+ */
+ // TODO: Support reporting the watermark, currently the watermark never
advances.
+ @UnboundedPerElement
+ static class UnboundedSourceAsSDFWrapperFn<OutputT, CheckpointT extends
CheckpointMark>
+ extends DoFn<UnboundedSource<OutputT, CheckpointT>,
ValueWithRecordId<OutputT>> {
+
+ private static final int DEFAULT_DESIRED_NUM_SPLITS = 20;
Review comment:
The default in Dataflow is `4 * first non-null of (maxNumWorkers,
numWorkers, 5)`:
https://github.com/apache/beam/blob/860131b5d47c830b772d3f1665a26a45ec85ab36/runners/google-cloud-dataflow-java/src/main/java/org/apache/beam/runners/dataflow/internal/CustomSources.java#L51
(I like the TODO in the method)
Which is why I went with 20 as the default.
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