Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/5717#discussion_r32330289
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeJoin.scala
---
@@ -84,84 +129,164 @@ case class SortMergeJoin(
override final def next(): Row = {
if (hasNext) {
- // we are using the buffered right rows and run down left
iterator
- val joinedRow = joinRow(leftElement,
rightMatches(rightPosition))
- rightPosition += 1
- if (rightPosition >= rightMatches.size) {
- rightPosition = 0
- fetchLeft()
- if (leftElement == null || keyOrdering.compare(leftKey,
matchKey) != 0) {
- stop = false
- rightMatches = null
+ if (bufferedMatches == null || bufferedMatches.size == 0) {
+ // we just found a row with no join match and we are here to
produce a row
+ // with this row with a standard null row from the other
side.
+ if (continueStreamed) {
+ val joinedRow = smartJoinRow(streamedElement,
bufferedNullRow.copy())
+ fetchStreamed()
+ joinedRow
+ } else {
+ val joinedRow = smartJoinRow(streamedNullRow.copy(),
bufferedElement)
+ fetchBuffered()
+ joinedRow
+ }
+ } else {
+ // we are using the buffered right rows and run down left
iterator
+ val joinedRow = smartJoinRow(streamedElement,
bufferedMatches(bufferedPosition))
+ bufferedPosition += 1
+ if (bufferedPosition >= bufferedMatches.size) {
+ bufferedPosition = 0
+ if (joinType != FullOuter || secondStreamedElement ==
null) {
+ fetchStreamed()
+ if (streamedElement == null ||
keyOrdering.compare(streamedKey, matchKey) != 0) {
+ stop = false
+ bufferedMatches = null
+ }
+ } else {
+ // in FullOuter join and the first time we finish the
match buffer,
+ // we still want to generate all rows with streamed null
row and buffered
+ // rows that match the join key but not the conditions.
+ streamedElement = secondStreamedElement
+ bufferedMatches = secondBufferedMatches
+ secondStreamedElement = null
+ secondBufferedMatches = null
+ }
}
+ joinedRow
}
- joinedRow
} else {
// no more result
throw new NoSuchElementException
}
}
- private def fetchLeft() = {
- if (leftIter.hasNext) {
- leftElement = leftIter.next()
- leftKey = leftKeyGenerator(leftElement)
+ private def smartJoinRow(streamedRow: Row, bufferedRow: Row): Row
= joinType match {
+ case RightOuter => joinRow(bufferedRow, streamedRow)
+ case _ => joinRow(streamedRow, bufferedRow)
+ }
+
+ private def fetchStreamed() = {
+ if (streamedIter.hasNext) {
+ streamedElement = streamedIter.next()
+ streamedKey = streamedKeyGenerator(streamedElement)
} else {
- leftElement = null
+ streamedElement = null
}
}
- private def fetchRight() = {
- if (rightIter.hasNext) {
- rightElement = rightIter.next()
- rightKey = rightKeyGenerator(rightElement)
+ private def fetchBuffered() = {
+ if (bufferedIter.hasNext) {
+ bufferedElement = bufferedIter.next()
+ bufferedKey = bufferedKeyGenerator(bufferedElement)
} else {
- rightElement = null
+ bufferedElement = null
}
}
private def initialize() = {
- fetchLeft()
- fetchRight()
+ fetchStreamed()
+ fetchBuffered()
}
/**
* Searches the right iterator for the next rows that have matches
in left side, and store
* them in a buffer.
+ * When this is not a Inner join, we will also return true when we
get a row with no match
+ * on the other side. This search will jump out every time from
the same position until
+ * `next()` is called.
*
* @return true if the search is successful, and false if the
right iterator runs out of
* tuples.
*/
private def nextMatchingPair(): Boolean = {
--- End diff --
Reading through the old version of the code, one tricky thing that stood
out to me was the fact that if a consumer of this iterator calls `hasNext()`
followed by `next()`, then we end up calling `nextMatchingPair()` two times in
a row. It might be nice to add a comment here to explain why this is safe /
correct.
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