Company or project name

ClickHouse

Describe the situation

Some queries with one simple aggregate function can be optimized.

Currently, aggregation is performed using a hash table (or a similar data structure) with a value of char * pointed to Arena where the aggregate function states are allocated.

If there is just a single aggregate function with the size of state not greater than the size of a pointer and the alignment of state not greater than the alignment of a pointer, and if it is trivially destructible, and they don't use the -State combinator, we can avoid using Arena, and store the state directly in the hash table value instead of a pointer.

This will save one indirection.

Caveats: the aggregate function state should also be movable.

Which ClickHouse versions are affected?

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How to reproduce

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Expected performance

No response

Additional context

No response