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[SPARK-21492][SQL] Memory leak in SortMergeJoin #18694

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zhzhan wants to merge 2 commits into from
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[SPARK-21492][SQL] Memory leak in SortMergeJoin #18694

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b8acae2
fix memory leak on SortMergeJoin
Jul 20, 2017
2703c1f
solve review comments
Jul 21, 2017
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32 changes: 30 additions & 2 deletions sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeJoinExec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -179,6 +179,7 @@ case class SortMergeJoinExec(
currentRightMatches = null
currentLeftRow = null
rightMatchesIterator = null
smjScanner.destruct()
return false
}
}
Expand All @@ -188,6 +189,7 @@ case class SortMergeJoinExec(
return true
}
}
smjScanner.destruct()
false
}

Expand Down Expand Up @@ -266,6 +268,7 @@ case class SortMergeJoinExec(
}
}
}
smjScanner.destruct()
false
}

Expand Down Expand Up @@ -306,6 +309,7 @@ case class SortMergeJoinExec(
return true
}
}
smjScanner.destruct()
false
}

Expand Down Expand Up @@ -344,6 +348,7 @@ case class SortMergeJoinExec(
numOutputRows += 1
return true
}
smjScanner.destruct()
false
}

Expand Down Expand Up @@ -604,6 +609,12 @@ case class SortMergeJoinExec(
| }
| if (shouldStop()) return;
|}
|while ($leftInput.hasNext()) {
| $leftInput.next();
|}
while ($rightInput.hasNext()) {
| $rightInput.next();
|}
""".stripMargin
}
}
Expand Down Expand Up @@ -649,6 +660,11 @@ private[joins] class SortMergeJoinScanner(
// Initialization (note: do _not_ want to advance streamed here).
advancedBufferedToRowWithNullFreeJoinKey()

def destruct(): Unit = {
while (streamedIter.advanceNext()) {}
while (bufferedIter.advanceNext()) {}
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@cloud-fan cloud-fan Jul 21, 2017

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can you explain more where is the memory leak? Why we have to exhaust the iterators?

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@viirya viirya Jul 21, 2017 •
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I think if we don't advance to next rows, the iterators should not load the rows?** If you exhaust the iterators, it actually spend unnecessary time to pull and process those rows.

** Sort will consume the input iterator first to sort.

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@zhzhan zhzhan Jul 21, 2017 •
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It does introduce extra overhead. The other way is to introduce a new interface for RowIterator to destruct itself, which may be more elegant and need more change to core data structure. Memory leak is worse than extra overhead, because it causes more spill and other issues.

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@zhzhan zhzhan Jul 21, 2017

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Detail is explained below.

}

// --- Public methods ---------------------------------------------------------------------------

def getStreamedRow: InternalRow = streamedRow
Expand Down Expand Up @@ -915,7 +931,11 @@ private abstract class OneSideOuterIterator(

override def advanceNext(): Boolean = {
val r = advanceBufferUntilBoundConditionSatisfied() || advanceStream()
if (r) numOutputRows += 1
if (r) {
numOutputRows += 1
} else {
smjScanner.destruct()
}
r
}

Expand Down Expand Up @@ -947,6 +967,10 @@ private class SortMergeFullOuterJoinScanner(
advancedLeft()
advancedRight()

def destruct(): Unit = {
while (leftIter.advanceNext()) {}
while (rightIter.advanceNext()) {}
}
// --- Private methods --------------------------------------------------------------------------

/**
Expand Down Expand Up @@ -1103,7 +1127,11 @@ private class FullOuterIterator(

override def advanceNext(): Boolean = {
val r = smjScanner.advanceNext()
if (r) numRows += 1
if (r) {
numRows += 1
} else {
smjScanner.destruct();
}
r
}

Expand Down