[GitHub] [pinot] Jackie-Jiang commented on pull request #8758: Improve accuracy of aggregate group-by without order-by queries by adding a query rewriter to convert aggregate group-by only queries to add order-by

[GitBox <gi...@apache.org>]

Jackie-Jiang commented on PR #8758:
URL: https://github.com/apache/pinot/pull/8758#issuecomment-1135212171

   This solution can cause big performance impact on existing non-order-by queries if enabled.
   I'd suggest directly enhancing the query engine for group-by queries without order-by on aggregations. In the query executor:
   1. Implicitly order-by the group-by columns not included in the order-by if the explicit order-by clause have the same value for 2 groups
   2. If there is no aggregation in the order-by clause, we don't need to keep more groups than the `LIMIT`. We should make a priority queue + map solution to only keep track of the top `LIMIT` groups. This solution can always give the accurate result, but without adding too much overhead


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