Christopher Krah
88203d2515
The `Permutation.rename_column` docstring says it "only changes the name
of the column that is visible from this permutation". But
`permutation.py:868-870` adds the new name at the end of the selection
and then deletes the old key, so the renamed column also moves to the
last position. Hugging Face `datasets`, which `Permutation` mirrors
(#2725), keeps it in place. Positional formats feel it most:
`with_format("numpy")` swaps the feature order of every row.
Before, on `d97df0c`:
```
$ python repro.py <tree>/python/python # lancedb 0.41.0b12 extension, Python sources from the tree
['id', 'value']
['value', 'row_id']
[{'value': 0, 'row_id': 0}]
[[10 1]]
```
After:
```
$ python repro.py <tree>/python/python
['id', 'value']
['row_id', 'value']
[{'row_id': 0, 'value': 0}]
[[ 1 10]]
```
<details><summary>repro.py (its first output line,
<code>lancedb.__file__</code>, is cut above)</summary>
```python
import sys; sys.path.insert(0, sys.argv[1])
import tempfile
import lancedb
from lancedb.permutation import Permutation
print(lancedb.__file__)
db = lancedb.connect(tempfile.mkdtemp())
tbl = db.create_table("t", [{"id": i, "value": i * 10} for i in range(3)])
perm = Permutation.identity(tbl)
print(perm.column_names)
renamed = perm.rename_column("id", "row_id")
print(renamed.column_names)
print(renamed.__getitems__([0]))
print(renamed.with_format("numpy").__getitems__([1]))
```
</details>
For comparison, `datasets` 5.1.0 gives `['new_id', 'value']` for
`Dataset.from_dict({'id': [1, 2], 'value': [3, 4]}).rename_column('id',
'new_id').column_names`.
No issue exists for this. The fix rebuilds the selection dict in order.
The cost: code that renamed a column and then read it by position in
numpy batches (say `[:, -1]`) gets a different column after this, with
no error. `rename_columns` calls `rename_column` once per name, so it
gets the fix too. The tests that check schema order only rename `value`,
the last column, and `test_rename_rowid` checks membership but not
order. The new test renames `id`.
### Verification
```
# Python 3.12.6; lancedb 0.41.0b12 wheel from pypi.fury.io, its _lancedb.abi3.so copied into the tree; pylance 14.0.0-rc.1
$ PYTHONPATH=python python -m pytest python/tests/test_permutation.py -q -p no:cacheprovider
d97df0c: 72 passed in 2.53s
this branch: 73 passed in 2.36s
permutation.py reverted, test kept:
FAILED python/tests/test_permutation.py::test_rename_column_keeps_position
assert value: int64\nnew_id: int64 == new_id: int64\nvalue: int64
1 failed, 72 passed in 2.41s
$ ruff format --check . && ruff check . # ruff 0.9.9, as python.yml pins it
152 files already formatted
All checks passed!
# not run: pyright (its include list covers neither permutation.py nor tests/), the Rust build
```
@westonpace, this is your class from #2725. Do you want the docstring to
say outright that the column keeps its position? If so, I'll add that
line to both rename methods in this PR.
Signed-off-by: Christopher Krah <48338417+chrikrah@users.noreply.github.com>
LanceDB Python SDK
A Python library for LanceDB.
Installation
pip install lancedb
If no wheel is published for your platform, pip builds lancedb from the source distribution. That build needs a Rust toolchain and protoc (the Protocol Buffers compiler) on your PATH, and can take a while.
Pre-Haswell x86_64 hosts: lancedb-compat
The default lancedb wheel targets x86-64-haswell (AVX2 + FMA + F16C) for full performance on modern hardware. Pre-Haswell hosts — Intel Sandy Bridge / Ivy Bridge / Westmere; AMD Bulldozer / Piledriver / Steamroller — don't have AVX2 and crash with Illegal instruction at import lancedb.
For those hosts, install the lancedb-compat package instead:
pip install lancedb-compat
Same Python API (import lancedb works as usual). The compat wheel is compiled at the x86-64-v2 baseline (Nehalem-class) and uses runtime SIMD dispatch in the embedded lance crate to pick the right kernel tier (scalar / AVX / AVX+FMA / AVX2+FMA / AVX-512) at load time, so it still goes fast on modern hardware while running cleanly on the pre-Haswell silicon. Use lance.simd_info() from Python to verify which tier was selected.
lancedb and lancedb-compat install to the same lancedb/ namespace and conflict at install time. Pick one. To switch, pip uninstall lancedb first, then pip install lancedb-compat (or vice-versa).
If you need a custom baseline (or lancedb-compat isn't yet published for your platform), build from source with the override:
RUSTFLAGS="-C target-cpu=x86-64-v2" maturin build --release
pip install ./target/wheels/lancedb-*.whl
Preview Releases
Stable releases are created about every 2 weeks. For the latest features and bug fixes, you can install the preview release. These releases receive the same level of testing as stable releases, but are not guaranteed to be available for more than 6 months after they are released. Once your application is stable, we recommend switching to stable releases.
pip install --pre --extra-index-url https://pypi.fury.io/lancedb/ lancedb
Threading in CPU-limited containers
LanceDB uses separate pools for compute work and storage I/O. On a container with two visible CPUs, current releases intentionally use one compute worker by default; no manual configuration is needed. If every query logs an I/O core reservation warning on a two-CPU container, upgrade from LanceDB 0.21.1 or earlier.
The two commonly tuned environment variables control different resources:
LANCE_CPU_THREADSoverrides the number of compute workers. One worker is the appropriate setting for a two-CPU container when an explicit override is needed.LANCE_IO_THREADScontrols concurrent storage operations, not reserved CPU cores. Its default can be greater than the number of CPUs because I/O workers spend much of their time waiting for storage.
Keep the defaults unless measurements show that the workload benefits from an override. See the Lance threading model for the current defaults and tuning guidance.
Usage
Basic Example
import lancedb
db = lancedb.connect('<PATH_TO_LANCEDB_DATASET>')
table = db.open_table('my_table')
results = table.search([0.1, 0.3]).limit(20).to_list()
print(results)
Development
See CONTRIBUTING.md for information on how to contribute to LanceDB.