gianm commented on a change in pull request #8047: optimize single input column
multi-value expressions
URL: https://github.com/apache/incubator-druid/pull/8047#discussion_r309497062
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File path:
processing/src/main/java/org/apache/druid/segment/virtual/ExpressionSelectors.java
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@@ -230,8 +230,9 @@ public static DimensionSelector makeDimensionSelector(
&& capabilities.getType() == ValueType.STRING
&& capabilities.isDictionaryEncoded()
&& capabilities.isComplete()
- && !capabilities.hasMultipleValues()
- && !exprDetails.getArrayColumns().contains(column)
+ && !exprDetails.hasInputArrays()
+ && !exprDetails.isOutputArray()
+ && (!capabilities.hasMultipleValues() ||
exprDetails.getFreeVariables().size() == 1)
) {
// Optimization for dimension selectors that wrap a single underlying
string column.
Review comment:
The flag chain above is getting complicated!
Could you please alter this comment to reflect what it's looking for? If I
understand it right, that should be something like:
> Optimization for dimension selectors that wrap a single underlying string
column. The string column can be multi-valued, but if so, it must be implicitly
mappable (i.e. the expression is not treating it as an array, not wanting to
output an array, and the multi-value dimension appears exactly once).
By the way, I have to assume logic like this is being used elsewhere to
implicitly map expressions that go through the non-optimized selector. Is there
any opportunity to extract the logic into a common helper method? It would make
it easier for readers and probably less error prone too.
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