Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/19594#discussion_r157503949
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/EstimationUtils.scala
---
@@ -212,4 +213,186 @@ object EstimationUtils {
}
}
+ /**
+ * Returns overlapped ranges between two histograms, in the given value
range
+ * [lowerBound, upperBound].
+ */
+ def getOverlappedRanges(
+ leftHistogram: Histogram,
+ rightHistogram: Histogram,
+ lowerBound: Double,
+ upperBound: Double): Seq[OverlappedRange] = {
+ val overlappedRanges = new ArrayBuffer[OverlappedRange]()
+ // Only bins whose range intersect [lowerBound, upperBound] have join
possibility.
+ val leftBins = leftHistogram.bins
+ .filter(b => b.lo <= upperBound && b.hi >= lowerBound)
+ val rightBins = rightHistogram.bins
+ .filter(b => b.lo <= upperBound && b.hi >= lowerBound)
+
+ leftBins.foreach { lb =>
+ rightBins.foreach { rb =>
+ val (left, leftHeight) = trimBin(lb, leftHistogram.height,
lowerBound, upperBound)
+ val (right, rightHeight) = trimBin(rb, rightHistogram.height,
lowerBound, upperBound)
+ // Only collect overlapped ranges.
+ if (left.lo <= right.hi && left.hi >= right.lo) {
+ // Collect overlapped ranges.
+ val range = if (left.lo == left.hi) {
+ // Case1: the left bin has only one value
+ OverlappedRange(
+ lo = left.lo,
+ hi = left.lo,
+ leftNdv = 1,
+ rightNdv = 1,
+ leftNumRows = leftHeight,
+ rightNumRows = rightHeight / right.ndv
+ )
+ } else if (right.lo == right.hi) {
+ // Case2: the right bin has only one value
+ OverlappedRange(
+ lo = right.lo,
+ hi = right.lo,
+ leftNdv = 1,
+ rightNdv = 1,
+ leftNumRows = leftHeight / left.ndv,
+ rightNumRows = rightHeight
+ )
+ } else if (right.lo >= left.lo && right.hi >= left.hi) {
+ // Case3: the left bin is "smaller" than the right bin
+ // left.lo right.lo left.hi
right.hi
+ //
--------+------------------+------------+----------------+------->
+ if (left.hi == right.lo) {
+ // The overlapped range has only one value.
+ OverlappedRange(
+ lo = right.lo,
+ hi = right.lo,
+ leftNdv = 1,
+ rightNdv = 1,
+ leftNumRows = leftHeight / left.ndv,
+ rightNumRows = rightHeight / right.ndv
+ )
+ } else {
+ val leftRatio = (left.hi - right.lo) / (left.hi - left.lo)
+ val rightRatio = (left.hi - right.lo) / (right.hi - right.lo)
+ OverlappedRange(
+ lo = right.lo,
+ hi = left.hi,
+ leftNdv = left.ndv * leftRatio,
+ rightNdv = right.ndv * rightRatio,
+ leftNumRows = leftHeight * leftRatio,
+ rightNumRows = rightHeight * rightRatio
+ )
+ }
+ } else if (right.lo <= left.lo && right.hi <= left.hi) {
+ // Case4: the left bin is "larger" than the right bin
+ // right.lo left.lo right.hi
left.hi
+ //
--------+------------------+------------+----------------+------->
+ if (right.hi == left.lo) {
+ // The overlapped range has only one value.
+ OverlappedRange(
+ lo = right.hi,
+ hi = right.hi,
+ leftNdv = 1,
+ rightNdv = 1,
+ leftNumRows = leftHeight / left.ndv,
+ rightNumRows = rightHeight / right.ndv
+ )
+ } else {
+ val leftRatio = (right.hi - left.lo) / (left.hi - left.lo)
+ val rightRatio = (right.hi - left.lo) / (right.hi - right.lo)
+ OverlappedRange(
+ lo = left.lo,
+ hi = right.hi,
+ leftNdv = left.ndv * leftRatio,
+ rightNdv = right.ndv * rightRatio,
+ leftNumRows = leftHeight * leftRatio,
+ rightNumRows = rightHeight * rightRatio
+ )
+ }
+ } else if (right.lo >= left.lo && right.hi <= left.hi) {
+ // Case5: the left bin contains the right bin
+ // left.lo right.lo right.hi
left.hi
+ //
--------+------------------+------------+----------------+------->
+ val leftRatio = (right.hi - right.lo) / (left.hi - left.lo)
+ OverlappedRange(
+ lo = right.lo,
+ hi = right.hi,
+ leftNdv = left.ndv * leftRatio,
+ rightNdv = right.ndv,
+ leftNumRows = leftHeight * leftRatio,
+ rightNumRows = rightHeight
+ )
+ } else {
+ assert(right.lo <= left.lo && right.hi >= left.hi)
+ // Case6: the right bin contains the left bin
+ // right.lo left.lo left.hi
right.hi
+ //
--------+------------------+------------+----------------+------->
+ val rightRatio = (left.hi - left.lo) / (right.hi - right.lo)
+ OverlappedRange(
+ lo = left.lo,
+ hi = left.hi,
+ leftNdv = left.ndv,
+ rightNdv = right.ndv * rightRatio,
+ leftNumRows = leftHeight,
+ rightNumRows = rightHeight * rightRatio
+ )
+ }
+ overlappedRanges += range
+ }
+ }
+ }
+ overlappedRanges
+ }
+
+ /**
+ * Given an original bin and a value range [lowerBound, upperBound],
returns the trimmed part
+ * of the bin in that range and its number of rows.
+ */
+ def trimBin(bin: HistogramBin, height: Double, lowerBound: Double,
upperBound: Double)
--- End diff --
maybe explain in the comment that `height` means the average number of rows
of the given bin inside a equi-height histogram.
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