gianm commented on a change in pull request #10285:
URL: https://github.com/apache/druid/pull/10285#discussion_r470809516
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File path: docs/development/extensions-core/stats.md
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@@ -44,6 +44,13 @@ This algorithm was proven to be numerically stable by J.L.
Barlow in
"Error analysis of a pairwise summation algorithm to compute sample variance"
Numer. Math, 58 (1991) pp. 583--590
+> As with all [aggregators](../../querying/sql.md#aggregation-functions), the
order of operations across segments is
+> non-deterministic. This means that if this aggregator is used with an input
type of "float", the result of the
+> aggregation will not be precisely the same across multiple runs of the query.
+>
+> To produce consistent results, either cast the input type to a "double" or
round the variance to
Review comment:
Double and float are both floating-point, so should behave the same way
in this regard.
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File path: docs/querying/sql.md
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@@ -232,6 +232,10 @@ possible for two aggregators in the same SQL query to have
different filters.
Only the COUNT aggregation can accept DISTINCT.
+> The order of aggregation operations across segments is not deterministic.
This means that non-commutative aggregation
+> functions can produce inconsistent results across the same query. Any
functions that operate on an input type of "float"
+> may also see these differences in aggregation results across multiple query
runs.
Review comment:
Similar comment.
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