ic4y commented on pull request #1520:
URL:
https://github.com/apache/arrow-datafusion/pull/1520#issuecomment-1004941980
From
```rust
struct Accumulators {
map: RawTable<(u64, usize)>,
group_states: Vec<GroupState>,
}
```
To
```rust
struct Accumulators {
map: RawTable<(u64, usize)>,
group_states:BumpVec<GroupState>,
}
```
By using bumpalo to allocate memory for group_states, the time to destruct
group_states can be greatly reduced in the case of high cardinality, and the
time consumption of destructuring group_states is almost not counted in pprf
The total test data is 350 million, and the deduplication number of user_id
is 50 million。
`sql : select count(1) from (select user_id from event group by user_id)a`
**master:**
drop_in_place<GroupState> takes 6s(50%) ，total 14s
**bumpalo:**
drop_in_place<GroupState> takes 0s(not counted) ，total 8s(40%
increase)
Under the TPC-H benchmark test, there is almost no difference. I think the
reason is that the grouping base is not high enough.
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