Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/15990#discussion_r89351269
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/HyperLogLogPlusPlus.scala
---
@@ -306,7 +307,7 @@ case class HyperLogLogPlusPlus(
val estimate = if (V > 0) {
// Use linear counting for small cardinality estimates.
val H = m * Math.log(m / V)
- if (H <= THRESHOLDS(p - 4)) {
+ if ((p < 19 && H <= THRESHOLDS(p - 4)) || E <= 2.5 * m) {
--- End diff --
I know the 2.5m bit is from the Flajolet paper but was it just missing here
before?
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