Jack Ye
6ed3074d4c
A permutation stores `_rowid`s, which are row addresses unless stable row ids are enabled. Nothing in the data loader pinned a table version, so a compaction between building a permutation and reading it can resolve those ids to different rows. The exposure differs by backend but exists on both: - Remote never pins. `prepare_query_bodies` stamps `"version": current_version()` on every request, but `current_version()` is `None` unless `checkout` was called, so every request means "latest". - Native pins implicitly by holding an `Arc<Dataset>` under `ConsistencyMode::Lazy`, but `StreamingDataset.__setstate__` reopens the table in each DataLoader worker, so each worker pins to whatever is latest at fork time. ## Changes `Table::at_version` returns an independent handle pinned to a version without mutating the receiver. `checkout` cannot serve this: on remote the version cell is an `Arc<RwLock<Option<u64>>>` shared across clones, so pinning through it would silently pin the caller's table too. `PermutationBuilder::build` pins for the whole build and records the version in the permutation table's schema metadata, alongside the existing split names. `PermutationReader` pins the base table to that version before any take. Because the reader pins on construction, the Python worker fork is covered without touching the pickle format — `Permutation.__setstate__` drops the reader and `_ensure_open` rebuilds it, which re-pins. ## Behaviour change A permutation is now bound to the version it was built against, so rows appended to the base table afterwards are not visible through an existing permutation. That is the intended semantics — the permutation only addresses rows that existed when it was built — but it is a change worth flagging. Permutations written before this carry no version key and read exactly as they did before.
LanceDB Python SDK
A Python library for LanceDB.
Installation
pip install lancedb
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.