imply-cheddar commented on a change in pull request #12291:
URL: https://github.com/apache/druid/pull/12291#discussion_r816443116
##########
File path:
processing/src/main/java/org/apache/druid/query/topn/types/StringTopNColumnAggregatesProcessor.java
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@@ -172,6 +180,54 @@ private long scanAndAggregateWithCardinalityKnown(
return processedRows;
}
+ /**
+ * this method uses hash table to store aggregate values ({@link
#aggregatesStore}) and is geared towards selectors
+ * which have a dictionary, but those dictionary ids do not necessarily
uniquely map to the value of
+ * {@link DimensionSelector#lookupName(int)}. This method keeps a cache of
dictionary id to aggregators, which it uses
+ * to skip name lookup if that id has already been encountered, avoiding
decoding utf8 bytes, or worse, recomputing
+ * an expression virtual column or some lookup value.
+ *
+ */
+ private long scanAndAggregateWithDictionary(
+ TopNQuery query,
+ Cursor cursor,
+ DimensionSelector selector
+ )
+ {
+ Int2ObjectOpenHashMap<Aggregator[]> aggsCache = new
Int2ObjectOpenHashMap<>();
Review comment:
With the test for `hasDictionary` we could perhaps make this
```
Aggregator[][] aggsCache = new Aggregator[selector.getValueCardinality()][];
```
?
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