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[WIP][SPARK-29221][SQL] LocalTableScanExec: handle the case where executors are accessing "null" rows #25913

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[WIP][SPARK-29221][SQL] LocalTableScanExec: handle the case where executors are accessing "null" rows #25913

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[SPARK-29221][SQL] LocalTableScanExec: handle the case rows is "null"…
HeartSaVioR Sep 24, 2019
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HeartSaVioR Sep 25, 2019
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6 changes: 4 additions & 2 deletions sql/core/src/main/scala/org/apache/spark/sql/execution/LocalTableScanExec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,7 @@ case class LocalTableScanExec(
"numOutputRows" -> SQLMetrics.createMetric(sparkContext, "number of output rows"))

@transient private lazy val unsafeRows: Array[InternalRow] = {
if (rows.isEmpty) {
if (rows == null || rows.isEmpty) {
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We cannot remove @transient instead of this?

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Adding transient is to avoid serializing and copying whole rows, so I guess it's preferred one.

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Related commits are here:
256358f
f70f46d

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Ah, I see. I'm a bit worried that this value could be different between a driver and executors. Which code touches this variable in executors? What's the stacktrace for unsafeRows?

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Uh, that's actually a kind of defensive programming, as it would bring NPE if there's no check for null. I haven't seen any actual stack trace to refer to unsafeRows.

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@maropu maropu Sep 25, 2019 •
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I personally think unsafeRows is not expected to be called in executor sides, so we need to check assert(rows != null) instead of the current approach. If it fails then, we need to fix some code not to call this variable in executors.

Array.empty
} else {
val proj = UnsafeProjection.create(output, output)
Expand All @@ -59,7 +59,9 @@ case class LocalTableScanExec(
}

override protected def stringArgs: Iterator[Any] = {
if (rows.isEmpty) {
if (rows == null) {
Iterator("<unknown>", output)
} else if (rows.isEmpty) {
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Is it ok to return different values in a driver and executors? How about computing this value in a driver then passing into executors?

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@HeartSaVioR HeartSaVioR Sep 24, 2019 •
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The value except output should be meaningless, otherwise assumption in related comments goes wrong and we should serialize the rows. I guess that's only for visual.

Iterator("<empty>", output)
} else {
Iterator(output)
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