Parallelize ClickHouse aggregation merge for fixed hash map
I recently worked on https://github.com/ClickHouse/ClickHouse/pull/87366. The idea is simple but learned a lot of ClickHouse aggregation, so want to jot it down.
Background
The original issue stated it clear, if you run almost identical queries, their performances varies a lot!
milovidov-pc :) SELECT number % 10000