PostgreSQL 19 introduces a significant optimization for data aggregation, allowing the database to aggregate data before performing joins. This change can greatly enhance performance without requiring any alterations to existing code. However, some complex features, like `GROUP BY CUBE`, may not fully benefit from this improvement.

This article discusses a new optimization in ClickHouse 25.11 that enhances the performance of aggregations with small GROUP BY keys by parallelizing the merge phase. The author shares insights from the implementation process, including challenges faced and lessons learned about memory management and concurrency.