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fix vector grouping expression deferred evaluation to only consider dictionary encoded strings as fixed width #16666

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merged 3 commits into from
Jun 27, 2024
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fix vector grouping expression deferred evaluation to only consider dictionary encoded strings as fixed width #16666

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48fc029
fix vector grouping expression deferred evaluation to only consider d…
clintropolis Jun 27, 2024
eb044c5
tests
clintropolis Jun 27, 2024
783eb64
fix strange
clintropolis Jun 27, 2024
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23 changes: 21 additions & 2 deletions processing/src/main/java/org/apache/druid/query/groupby/DeferExpressionDimensions.java
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,7 @@ public boolean useDeferredGroupBySelector(
return false;
}

if (!capabilities.isNumeric() && !capabilities.isDictionaryEncoded().isTrue()) {
if (!capabilities.isNumeric() && !isDictionaryEncodedScalarString(capabilities)) {
// Not fixed-width.
return false;
}
Expand Down Expand Up @@ -106,7 +106,7 @@ public boolean useDeferredGroupBySelector(

allNumericInputs = allNumericInputs && capabilities.isNumeric();

if (!capabilities.isNumeric() && !capabilities.isDictionaryEncoded().isTrue()) {
if (!capabilities.isNumeric() && !isDictionaryEncodedScalarString(capabilities)) {
// Not fixed-width.
return false;
}
Expand Down Expand Up @@ -162,6 +162,25 @@ public String toString()
return jsonName;
}


/**
* {@link VectorColumnSelectorFactory} currently can only make dictionary encoded selectors for string types, so
* we can only consider them as fixed width. Additionally, to err on the side of safety, multi-value string columns
* are also not considered fixed width because expressions process multi-value dimensions as single rows, so we would
* need all dictionary ids to be present in the combined key.
*
* At the time of this javadoc, vector group by does not support multi-value dimensions anyway, so this isn't really
* a problem, but if it did, we could consider allowing them if we ensure that all multi-value inputs are used as
* scalars and so the expression can be applied separately to each individual dictionary id (e.g. the equivalent of
* {@link ExpressionPlan.Trait#SINGLE_INPUT_MAPPABLE} but for all multi-value string inputs of the expression).
*/
private static boolean isDictionaryEncodedScalarString(ColumnCapabilities capabilities)
{
return capabilities.isDictionaryEncoded().isTrue() &&
capabilities.is(ValueType.STRING) &&
capabilities.hasMultipleValues().isFalse();
}

/**
* Whether the given expression can be deferred innately by the selector created by
* {@link ExpressionVirtualColumn#makeSingleValueVectorDimensionSelector(DimensionSpec, VectorColumnSelectorFactory)}.
Expand Down
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