gene-bordegaray opened a new pull request, #20331:
URL: https://github.com/apache/datafusion/pull/20331
## Which issue does this PR close?
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Closes #20195
## Rationale for this change
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the issue then this section is not needed.
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Dynamic filter pushdown was completely when `preserve_file_partitions` on
due to a correctness bug.
**The Problem**
When preserve_file_partitions enabled, DataFusion treats file groups as
pre-partitioned data. Existing dynamic filtering used hash-based routing which
is incompatible with the value-based partitioning that file groups are kept in:
Example:
```
Table partitioned by col_a:
- Partition 0: col_a = 'A'
- Partition 1: col_a = 'B'
- Partition 2: col_a = 'C'
Dimension Table: values = ['A', 'B']
SELECT * FROM large_table
JOIN small_table ON large_table.col_a = small_table.col_a
Hash routing doesn't work:
- Hash routing: hash('A') % 3 might map to partition 1 (not partition 0)
- File partitioning: 'A' data is in partition 0 (value-based)
```
For this reason was diabled, this PR re-enables it via `PartitionIndex`
routing for dynamic filters.
## What changes are included in this PR?
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sometimes worth providing a summary of the individual changes in this PR.
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**Partition-Indexed dynamic filtering**
New routing mode that uses direct partition-to-partition mapping:
```
Build partition 0 → filters Probe partition 0
Build partition 1 → filters Probe partition 1
Build partition 2 → filters Probe partition 2
```
Example:
```
HashJoinExec: mode=Partitioned, routing=PartitionIndex, on=[col_a = col_b]
DataSourceExec: table_large, file_groups={3: [col_a=A], [col_a=B],
[col_a=C]} predicate=DynamicFilter[
{0: col_a IN ['A','B']}, -- Partition 0 filtered
{1: col_a IN ['A','B']}, -- Partition 1 filtered
{2: col_a IN ['A','B']} -- Partition 2 filtered (no matches, pruned)
]
DataSourceExec: table_small, values: [col_b='A', col_b='B']
How it works:
- Build partition 0 (col_b='A') creates filter for probe partition 0
(col_a='A')
- Build partition 1 (col_b='B') creates filter for probe partition 1
(col_a='B')
- Probe partition 2 (col_a='C') gets pruned (no matching build partition)
```
**Alignment Detection**
Detects compatible partitioning to enable safe optimization:
- Both sides file-grouped (value-based partitioning) -> PartitionIndex
- Both sides hash-repartitioned (hash-based partitioning) -> CashHash
- Both has different partitioning -> Error, this shouldn't happen and can
cause incorrect results
match (left.repartitioned, right.repartitioned) {
In the case there is a `RepartitionExec` in the path leading from the
`DataSourceExec` to either the build or probe side of a Partitioned Hash Join
-> Falls back to CaseHash.
The reason is `RepartitionExec` uses hash(value) % N to distribute rows,
breaking the value-based partition alignment. When hash-partitioned, partition
0 no longer contains 'A' exclusively, breaking the partition index assumptions
With hash partitioning, use:
```
CASE hash(col_a) % 4
WHEN 0 THEN filter_partition_0
WHEN 1 THEN filter_partition_1
...
END
```
## Are these changes tested?
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sqlogictests: test_files/preserve_file_partitioning.slt
Integration tests:
datafusion/core/tests/physical_optimizer/filter_pushdown.rs
Unit tests: in effected files
## Are there any user-facing changes?
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updated before approving the PR.
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Yes a new error message can appear is partition hash joins are not aligned
properly and the dynamic filtering display for partition index is a but
different then CASE routing.
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