[SPARK-30671][SQL] emptyDataFrame should use a LocalRelation #27400
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cc @HyukjinKwon can you take a look? |
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makes sense, +1 |
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Test build #117560 has finished for PR 27400 at commit
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MaxGekk
reviewed
Jan 30, 2020
| lazy val emptyDataFrame: DataFrame = { | ||
| createDataFrame(sparkContext.emptyRDD[Row].setName("empty"), StructType(Nil)) | ||
| } | ||
| lazy val emptyDataFrame: DataFrame = Dataset.ofRows(self, LocalRelation()) |
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Suggested change
| lazy val emptyDataFrame: DataFrame = Dataset.ofRows(self, LocalRelation()) | |
| lazy val emptyDataFrame: DataFrame = emptyDataset(RowEncoder(new StructType())) |
?
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Why would that be better? This is basically re-implementing Dataset.ofRows.
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This is arguable for sure. DataFrame is Dataset[Row]. We already have a function which can construct empty Dataset[T], why not just re-use it. emptyDataFrame is some kind of specialization of emptyDataset.
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If we take this suggestion, maybe: emptyDataset(RowEncoder(StructType(Nil))).
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Dataset.ofRows(self, LocalRelation()) looks simpler as I don't need to jump into another method when reading the code.
HyukjinKwon
reviewed
Jan 31, 2020
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thanks, merging to master! |
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Let me merge instead. Seems hitting a network issue (?). |
HyukjinKwon
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Feb 12, 2020
…ions ### What changes were proposed in this pull request? This is a small follow-up for #27400. This PR makes an empty `LocalTableScanExec` return an `RDD` without partitions. ### Why are the changes needed? It is a bit unexpected that the RDD contains partitions if there is not work to do. It also can save a bit of work when this is used in a more complex plan. ### Does this PR introduce any user-facing change? No ### How was this patch tested? Added test to `SparkPlanSuite`. Closes #27530 from hvanhovell/SPARK-30780. Authored-by: herman <herman@databricks.com> Signed-off-by: HyukjinKwon <gurwls223@apache.org>
HyukjinKwon
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that referenced
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Feb 12, 2020
…ions ### What changes were proposed in this pull request? This is a small follow-up for #27400. This PR makes an empty `LocalTableScanExec` return an `RDD` without partitions. ### Why are the changes needed? It is a bit unexpected that the RDD contains partitions if there is not work to do. It also can save a bit of work when this is used in a more complex plan. ### Does this PR introduce any user-facing change? No ### How was this patch tested? Added test to `SparkPlanSuite`. Closes #27530 from hvanhovell/SPARK-30780. Authored-by: herman <herman@databricks.com> Signed-off-by: HyukjinKwon <gurwls223@apache.org> (cherry picked from commit b25359c) Signed-off-by: HyukjinKwon <gurwls223@apache.org>
sjincho
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Apr 15, 2020
…ions ### What changes were proposed in this pull request? This is a small follow-up for apache#27400. This PR makes an empty `LocalTableScanExec` return an `RDD` without partitions. ### Why are the changes needed? It is a bit unexpected that the RDD contains partitions if there is not work to do. It also can save a bit of work when this is used in a more complex plan. ### Does this PR introduce any user-facing change? No ### How was this patch tested? Added test to `SparkPlanSuite`. Closes apache#27530 from hvanhovell/SPARK-30780. Authored-by: herman <herman@databricks.com> Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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What changes were proposed in this pull request?
This PR makes
SparkSession.emptyDataFrameuse an empty local relation instead of an empty RDD. This allows to optimizer to recognize this as an empty relation, and creates the opportunity to do some more aggressive optimizations.Why are the changes needed?
It allows us to optimize empty dataframes better.
Does this PR introduce any user-facing change?
No.
How was this patch tested?
Added a test case to
DataFrameSuite.