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physical_optimizer: preserve_file_partitions when num file groups < target_partitions #21533

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physical_optimizer: preserve_file_partitions when num file groups < target_partitions #21533

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physical_optimizer: preserve_file_partitions when num file groups < t…
jayshrivastava Apr 10, 2026
bb11cd3
fix
jayshrivastava Apr 10, 2026
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8 changes: 7 additions & 1 deletion datafusion/physical-optimizer/src/enforce_distribution.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1328,8 +1328,14 @@ pub fn ensure_distribution(
})
);

let allow_subset_satisfy_partitioning = current_partitions
let allow_subset_satisfy_partitioning = (current_partitions
>= subset_satisfaction_threshold
// `preserve_file_partitions` exposes existing file-group
// partitioning to the optimizer. Respect it when the only
// reason to repartition would be to increase partition count
// beyond the preserved file-group count.
|| (config.optimizer.preserve_file_partitions > 0
&& current_partitions < target_partitions))
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@NGA-TRAN NGA-TRAN Apr 11, 2026

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👍
This condition is needed to preserve file partition even if current partition < target_partitions

&& !is_partitioned_join
&& !requires_grouping_id;

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54 changes: 54 additions & 0 deletions datafusion/sqllogictest/test_files/preserve_file_partitioning.slt
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Expand Up @@ -698,6 +698,60 @@ A dev 772.4
B prod 614.4
C prod 2017.6

##########
# TEST 13: Partitioned Join where Number of File Groups is less than target_partitions
# With preserve_file_partitions enabled, we should still avoid repartitioning
##########

statement ok
set datafusion.execution.target_partitions = 4;

statement ok
set datafusion.optimizer.preserve_file_partitions = 1;

query TT
EXPLAIN SELECT f_dkey, timestamp,
COUNT(*), AVG(value)
FROM fact_table
GROUP BY f_dkey, timestamp;
----
logical_plan
01)Projection: fact_table.f_dkey, fact_table.timestamp, count(Int64(1)) AS count(*), avg(fact_table.value)
02)--Aggregate: groupBy=[[fact_table.f_dkey, fact_table.timestamp]], aggr=[[count(Int64(1)), avg(fact_table.value)]]
03)----TableScan: fact_table projection=[timestamp, value, f_dkey]
physical_plan
01)ProjectionExec: expr=[f_dkey@0 as f_dkey, timestamp@1 as timestamp, count(Int64(1))@2 as count(*), avg(fact_table.value)@3 as avg(fact_table.value)]
02)--AggregateExec: mode=SinglePartitioned, gby=[f_dkey@2 as f_dkey, timestamp@0 as timestamp], aggr=[count(Int64(1)), avg(fact_table.value)]
03)----DataSourceExec: file_groups={3 groups: [[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/preserve_file_partitioning/fact/f_dkey=A/data.parquet], [WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/preserve_file_partitioning/fact/f_dkey=B/data.parquet], [WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/preserve_file_partitioning/fact/f_dkey=C/data.parquet]]}, projection=[timestamp, value, f_dkey], file_type=parquet
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@NGA-TRAN NGA-TRAN Apr 11, 2026

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Nice. We want to keep these 3 partitions as-is. We do not want to repartition it to the number of target_partitions


query TPIR rowsort
SELECT f_dkey, timestamp,
COUNT(*), AVG(value)
FROM fact_table
GROUP BY f_dkey, timestamp;
----
A 2023-01-01T09:00:00 1 95.5
A 2023-01-01T09:00:10 1 102.3
A 2023-01-01T09:00:20 1 98.7
A 2023-01-01T09:12:20 1 105.1
A 2023-01-01T09:12:30 1 100
A 2023-01-01T09:12:40 1 150
A 2023-01-01T09:12:50 1 120.8
B 2023-01-01T09:00:00 1 75.2
B 2023-01-01T09:00:10 1 82.4
B 2023-01-01T09:00:20 1 78.9
B 2023-01-01T09:00:30 1 85.6
B 2023-01-01T09:12:30 1 80
B 2023-01-01T09:12:40 1 120
B 2023-01-01T09:12:50 1 92.3
C 2023-01-01T09:00:00 1 300.5
C 2023-01-01T09:00:10 1 285.7
C 2023-01-01T09:00:20 1 310.2
C 2023-01-01T09:00:30 1 295.8
C 2023-01-01T09:00:40 1 300
C 2023-01-01T09:12:40 1 250
C 2023-01-01T09:12:50 1 275.4

##########
# CLEANUP
##########
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