[Enhancement]: local reduce can be optimized if only one segment is involved

[longjiquan]

Is there an existing issue for this?

• [X] I have searched the existing issues

What would you like to be added?

https://github.com/milvus-io/milvus/blob/77f4f0c5a82f71c148a10e4719df48033dfd4d6c/internal/core/src/segcore/Reduce.cpp#L222-L311

Why is this needed?

If only one segment was involved in the reduce phase, in fact we waste the cpu of heap-sort to complete the reduce. We can do it more simply.

Anything else?

No response

[longjiquan]

the tracing can be found in https://github.com/milvus-io/milvus/pull/32734

[xiaofan-luan]

seems to be a promising optimization

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