apache / apache/datafusion-python
Simplified filter expression has a Null type instead of Int64 type across the FFI layer
- Dominant language
- Python
- Stars
- 604
- Forks
- 174
- Avg merge
- 1d 7h
- Merged PRs (30d)
- 4
Description
**Describe the bug**
A custom table provider for a ParquetSource with a trivial catalog and an Int64 column yields some errors when a SQL query has a filter with a literal limit on that column of the form
```
assertion `left == right` failed: Simplified expression should have the same data type as the original
left: Null
right: Int64
```
The error does not occur when using datafusion-python 52; it also does not occur when running the query purely in a Rust SessionContext; the backtrace for the above error shows it coming from datafusion-ffi code as well.
This may of course not be a bug, but instead some bad practice that the version 52 set of crates tolerates but which is now invalid. A MRE of this custom table provider can be found in the public repo https://github.com/jwimberl/datafusion_python_53_int64filter_repro, which contains
- a non-working datafusion53 version (in branch [main](https://github.com/jwimberl/datafusion_python_53_int64filter_repro))
- a baseline working version (in branch [datafusion52](https://github.com/jwimberl/datafusion_python_53_int64filter_repro/tree/datafusion52))
and a canned dummy dataset. The README.md of this repo has more details.
**To Reproduce**
In the `main` branch, build the `py_repro_provider` crate with `maturin develop` and run `python repro.py`. This loads the dummy dataset as a table `dummy_table` and runs two queries
- `SELECT * FROM dummy_table LIMIT 1`, which is successful
- `SELECT * FROM dummy_table LIMIT 5`, which panics
Itss output should be something like
```
Successful query:
a b
0 0 42
Unsuccesful query:
thread '' panicked at /home/jwimberley/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/datafusion-physical-expr-53.1.0/src/simplifier/mod.rs:76:17:
assertion `left == right` failed: Simplified expression should have the same data type as the original
left: Null
right: Int64
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
followed by backtrace information.
**Expected behavior**
In the `datafusion52` branch, build the`py_repro_provider` with `maturin develop` and run `python repro.py`. It runs the same two queries, and its output should be
```
Successful query:
a b
0 0 42
Also successful query:
a b
0 0 42
1 1 42
2 2 42
3 3 42
4 4 42
```
**Additional context**
In either the `main` branch or `datafusion52` branch, the Rust code for the table provider is in the directory `repro_provider`, and there is a corresponding cargo test that runs `SELECT * FROM dummy_table WHERE a < 5`. Without the FFI layer, this is successful with both datafusion 52 and 53.
Contributor guide
No contributing guide indexed for this repository
Research direction
Start with the linked MRE, especially repro.py and the repro_provider directory, then compare the main and datafusion52 branches. Run the maturin develop and python repro.py steps to reproduce the LIMIT 5 panic, and run the corresponding cargo test for SELECT * FROM dummy_table WHERE a < 5 to compare behavior with and without the FFI layer. Done means the FFI query succeeds without the Null-versus-Int64 assertion.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python, rust
- Domain
- backend, data-engineering
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 55/100