Will Jones
d2ca0ce0ab
Merge insert has always taken a list of columns to match on, and local tables have always joined on all of them. Remote tables did not: any list longer than one was rejected with `MergeInsertBuilder only supports a single 'on' column`, so a composite-key upsert was impossible against LanceDB Cloud and Enterprise from Rust, Python or TypeScript. The remote request now carries `on` as a list and sends it as one repeated query parameter per column — `?on=shard_key&on=id`. That is how the lance-namespace spec encodes an array-valued `on`, so the server receives a composite key in the shape it expects. A single column still serializes to `?on=id`, exactly what clients sent before, so existing callers are unaffected. A column repeated within `on` is now rejected client-side rather than sent for the server to reject with a 400. No binding changes were needed: `Table.merge_insert` in Python and `Table.mergeInsert` in TypeScript already accepted a list, it just could not reach a remote table. Both gain a test for composite keys, and the doc comments now say what passing several columns means. Part of [ENT-2084](https://linear.app/lancedb/issue/ENT-2084/mergeinsertintotablerequest-support-multiple-columns-for-the). ## Example ```python table.merge_insert(["shard_key", "id"]) \ .when_matched_update_all() \ .when_not_matched_insert_all() \ .execute(new_data) ``` A row whose `id` matches an existing row but whose `shard_key` differs is an insert, not an update. ## Not included Java. Java callers reach merge insert through `org.lance.namespace.LanceNamespace`, whose `MergeInsertIntoTableRequest.on` is a single string until lance-namespace 0.12 ([lance-namespace#363](https://github.com/lance-format/lance-namespace/pull/363), [lance#8915](https://github.com/lance-format/lance/pull/8915)). There is nothing in this repo's Java SDK to change until the `lance-core` pin can move. Sending more than one column requires a server that accepts the repeated parameter ([sophon#7571](https://github.com/lancedb/sophon/pull/7571)); an older server returns a 400 rather than silently merging on one column. Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
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.