gortiz commented on code in PR #8979:
URL: https://github.com/apache/pinot/pull/8979#discussion_r977481626
##########
pinot-core/src/main/java/org/apache/pinot/core/operator/combine/BaseCombineOperator.java:
##########
@@ -250,6 +250,18 @@ protected boolean isQuerySatisfied(T resultsBlock) {
*/
protected abstract void mergeResultsBlocks(T mergedBlock, T blockToMerge);
+ /**
+ * Converts the given generic IntermediateResultBlock into the specific type
of IntermediateResultBlock that is
+ * supported by this combine operator.
+ *
+ * This operator may return the same object if the runtime type of the given
block already matches which what it is
+ * expected.
+ *
+ * The returned object will usually be the one received as first argument of
+ * {@link #mergeResultsBlocks(BaseResultsBlock, BaseResultsBlock)}.
+ */
+ protected abstract T createInitialResultBlock(BaseResultsBlock block);
Review Comment:
I don't think we should use T here because it may be the case that the child
operator returns a different block type than the one used in the
BaseCombineOperator. By adding T here we:
- Need to cast the child operator, whose static type is usually Block or
BaseResultBlock, to T before calling this method.
- Couple the child operator and the combine operator when it is not needed.
I've just changed the code a little bit make this explicit by adding another
method such as:
```java
/**
* Converts the given generic BaseResultsBlock into the specific type of
BaseResultsBlock that is supported by this
* operator.
*
* This operator may return the same object if the runtime type of the
given block already matches which what it is
* expected.
*
* The returned object will usually be the one received as second argument
of
* {@link #mergeResultsBlocks(T, T)}
*/
protected T convertToAppendableBlock(BaseResultsBlock block) {
return (T) block;
}
```
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