2010YOUY01 opened a new pull request, #23309:
URL: https://github.com/apache/datafusion/pull/23309
## Which issue does this PR close?
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## Rationale for this change
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Part of https://github.com/apache/datafusion/issues/22710
Addressing @alamb ’s comment from
https://github.com/apache/datafusion/pull/23181#pullrequestreview-4602624169
The motivation behind the EPIC was that the existing aggregation code had
too many internal flags and was reused by many different execution paths,
making it hard to maintain. The previous refactor made two main changes:
1. Split different aggregation modes, such as partial and final, into
separate streams.
2. Split the hash tables used by different aggregation modes into separate
implementations.
Now that the refactor is almost done, with only single aggregation mode and
spilling behavior left, I think decision 1 was still solid, while **decision 2
was an overcorrection**.
A module usually becomes hard to maintain when it has many tightly coupled
internal flags. In the old `GroupsHashAggregateStream` case, there were ~10
such flags. But a small number of flags, I think <= 3, is still clean and
manageable.
This PR unifies the aggregate hash tables used by different modes into a
single implementation. The behavioral differences are controlled by one
internal `mode` flag. See the comments in `common.rs: struct
AggregateHashTable`, for details.
Since this refactor is close to completion, I can confirm the internal
complexity of `AggregateHashTable` is not likely to bloat in the long term, so
unifying these implementations seems like the better design.
## What changes are included in this PR?
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Replace separated aggregate hash table implementation with a unified one
## Are these changes tested?
Existing tests
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## Are there any user-facing changes?
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