lancedb-gatefixer[bot]
ae81d73563
<!-- lance-gatekeeper-fix:v1 agent=d30696bc46eb32f04c9927b0792e35d3 generation=1 --> ## Summary - use the Lance native batch KNN path so fixed-size batch vector searches share one flat table scan - validate consistent query-vector dimensions and retain the per-vector plan when offsets require its existing semantics - add Rust and Python regressions and update Rust, Python, and TypeScript API documentation ## Root cause LanceDB expanded every vector in a batch into a separate scan plan and joined the plans with `UnionExec`. For unindexed tables on S3, a batch of ten vectors therefore ran ten concurrent full scans, amplifying CPU and retained data enough to produce the reported memory spike. The native Lance batch KNN path performs bounded-memory selection for all query vectors over one flat scan. LanceDB now supplies the vectors as a batch and avoids applying a global scanner limit to the combined per-query results. Batch queries with a nonzero offset keep the previous plan because the native batch API does not support per-query offsets. ## Validation - targeted Rust batch-query plan and execution tests - `cargo check --quiet --features remote --tests --examples` - `cargo clippy --quiet --features remote --tests --examples` - `cargo fmt --all -- --check` - targeted Python batch-vector regression after rebuilding the extension - Ruff formatting/checks for the touched Python files - Node.js build, lint, docs generation, and targeted batch-vector Jest test - `git diff --check` Fixes #2468 --------- Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com> Co-authored-by: Xuanwo <github@xuanwo.io>
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.