Improve performance of last_value by implementing special GroupsAccumulator
#15542
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comphead
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Apr 4, 2025
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Thanks @UBarney I think this is a right direction, I would suggest though to split the PR into smaller. The fix itself is important however there is bunch of renames/code moves, etc. It would be nice to start with a PR with just a fix a performance benefits description?
| @@ -291,7 +202,121 @@ impl AggregateUDFImpl for FirstValue { | |||
| } | |||
| } | |||
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| struct FirstPrimitiveGroupsAccumulator<T> | |||
| fn create_group_acc( | |||
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Suggested change
| fn create_group_acc( | |
| fn create_group_accumulator( |
| fn create_group_acc( | ||
| args: AccumulatorArgs, | ||
| pick_first_in_group: bool, | ||
| ) -> std::result::Result<Box<dyn GroupsAccumulator>, DataFusionError> { |
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we can use DFResult instead of Result with DataFusionError
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@comphead Thanks for reviewing. I have split this PR. This PR only contains performance improvements. After this PR is merged, I will start a refactor PR to handle renames and code moves |
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Which issue does this PR close?
firstandlast#13998.Rationale for this change
Achieved significant performance improvement when cardinality is high.
select id2, id4, last_value(v1 order by id2, id4) as r2 from '~/h2o_100m.parquet' group by id2, id4;select l_shipmode, last_value(l_partkey order by l_orderkey, l_linenumber, l_comment, l_suppkey, l_tax) from 'benchmarks/data/tpch_sf10/lineitem' group by l_shipmode;What changes are included in this PR?
pick_first_in_group: booltoPrimitiveGroupsAccumulator. If ture take first element in an aggregation group according to the requested ordering, otherwisetake last elementAdditional context
#15266
Are these changes tested?
Yes
Are there any user-facing changes?
No