yashmayya commented on code in PR #13835:
URL: https://github.com/apache/pinot/pull/13835#discussion_r1743453260
##########
pinot-segment-spi/src/main/java/org/apache/pinot/segment/spi/index/startree/AggregationFunctionColumn.java:
##########
@@ -127,9 +149,14 @@ public boolean equals(Object obj) {
if (this == obj) {
return true;
}
- if (obj instanceof AggregationFunctionColumnPair) {
- AggregationFunctionColumnPair anotherPair =
(AggregationFunctionColumnPair) obj;
- return _functionType == anotherPair._functionType &&
_column.equals(anotherPair._column);
+ if (obj instanceof AggregationFunctionColumn) {
+ AggregationFunctionColumn other = (AggregationFunctionColumn) obj;
+ // TODO: Revisit this since it means that for aggregation functions
where a certain config parameter need not be
+ // checked to determine whether a query can be served by a star-tree
index, we won't rebuild a star-tree index
+ // if the parameter value is changed in the index configuration.
+ return _functionType == other._functionType &&
_column.equals(other._column)
+ &&
AggregationFunctionType.compareFunctionParametersForStarTree(_functionType,
_functionParameters,
+ other._functionParameters) == 0;
Review Comment:
Hm actually I just realized that there's an assumption probably baked into
many places that one star-tree can't have multiple pre-aggregations for the
same aggregation function / column pair (see
[here](https://github.com/apache/pinot/blob/d411f34b869aaecad803a1dde659a712c8e8c18a/pinot-core/src/main/java/org/apache/pinot/core/startree/plan/StarTreeProjectPlanNode.java#L61-L91)
for instance where we're using the `functionName__columnName` to retrieve data
from the star-tree). I think it might be cleaner overall to make this
assumption explicit now that we're introducing configurable function parameters
- essentially add a table config validation that prevents a single star-tree
index configuration (`StarTreeIndexConfig`) from having multiple configurations
for the same function / column in `StarTreeAggregationConfig`. So, if a user
wants to have a pre-aggregation on `DISTINCTCOUNTHLL(col, 16)` as well as
`DISTINCTCOUNTHLL(col, 8)` for some reason, these should be configured in sepa
rate star-trees. This way we can safely continue to use the existing logic for
retrieving data from a star-tree index once it has already been matched for a
query.
I agree with your comment on generalizing the logic of matching aggregations
in `StarTreeUtils.createStarTreeBasedProjectOperator()` though. I like your
idea of modifying the `AggregationFunction` interface to allow each aggregation
to decide whether a particular star-tree index can be used. Although I'm
thinking that given the above observations on not having multiple entities for
the same function / column pair in a single star-tree, we can extract the
function parameters out of this `AggregationFunctionColumn` class (reverting it
to what it was earlier). We can instead maintain the function parameters
alongside the existing info in something like a
`Map<AggregationFunctionColumnPair, Pair<Map<String, Object>, AggregationSpec>`
(which also seems easier to reason about) in `StarTreeV2BuilderConfig`,
`StarTreeV2Metadata` etc. WDYT?
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