theirix opened a new pull request, #13475:
URL: https://github.com/apache/datafusion/pull/13475
## Which issue does this PR close?
When using pushdown filters, the planner pushes the volatile `random()`
filter to the table source, so it executes in scan (for example, in parquet)
and in the query engine, which leads to weird results.
Closes #13268.
## Rationale for this change
It's impossible to evaluate volatile filters in different layers.
## What changes are included in this PR?
- Improvement for rule optimiser to avoid passing volatile filters to scan
- Unit test
## Are these changes tested?
- Unit tests
- Regression tests
- Manual test
As proposed in the original issue, I tried
`alltypes_tiny_pages_plain.parquet` sample file containing 7300 lines:
```sql
set datafusion.execution.parquet.pushdown_filters=true;
create external table data stored as parquet location
'alltypes_tiny_pages_plain.parquet';
```
Running a query
```sql
select COUNT(*) from data WHERE RANDOM() < 0.1;
```
with `datafusion-cli` gives an answer of 726, which is pretty close to the
expected 730.
New plan
```
+---------------+---------------------------------------------------------------------------------+
| plan_type | plan
|
+---------------+---------------------------------------------------------------------------------+
| logical_plan | Aggregate: groupBy=[[]], aggr=[[count(Int64(1)) AS
count(*)]] |
| | Filter: random() < Float64(0.1)
|
| | TableScan: data projection=[]
|
| physical_plan | AggregateExec: mode=Final, gby=[], aggr=[count(*)]
|
| | CoalescePartitionsExec
|
| | AggregateExec: mode=Partial, gby=[], aggr=[count(*)]
|
| | CoalesceBatchesExec: target_batch_size=8192
|
| | FilterExec: random() < 0.1
|
| | RepartitionExec:
partitioning=RoundRobinBatch(8), input_partitions=1 |
| | ParquetExec: file_groups={1 group:
[[sample.parquet]]} |
| |
|
+---------------+---------------------------------------------------------------------------------+
```
Before the change plan was
```
| ParquetExec: file_groups={1 group: [[alltypes_tiny_pages_plain.parquet]]},
predicate=random() < 0.1 |
```
## Are there any user-facing changes?
No breaking changes.
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