## Summary
Split out from #3354
Adds `LsmWriteSpec` and `Table::set_lsm_write_spec` /
`unset_lsm_write_spec` to
install and clear the spec that selects Lance's MemWAL LSM-style write
path for
`merge_insert`.
`LsmWriteSpec` offers three sharding strategies, all built on Lance's
`InitializeMemWalBuilder`:
- `LsmWriteSpec::bucket(column, num_buckets)` — hash-bucket sharding by
the
single-column unenforced primary key.
- `LsmWriteSpec::identity(column)` — identity sharding by the raw value
of a
scalar column.
- `LsmWriteSpec::unsharded()` — a single MemWAL shard.
Each can be refined with `with_maintained_indexes(...)` (indexes the
MemWAL
keeps up to date as rows are appended) and
`with_writer_config_defaults(...)`
(default `ShardWriter` configuration recorded in the MemWAL index, so
every
writer starts from the same defaults). All variants require the table to
have
an unenforced primary key.
- `set_lsm_write_spec` installs the spec by initializing the MemWAL
index;
`unset_lsm_write_spec` removes it (dropping the MemWAL index), reverting
to
the standard `merge_insert` path. `unset` is idempotent.
- Bindings: Python (`LsmWriteSpec.bucket` / `.identity` / `.unsharded`,
`set_lsm_write_spec` / `unset_lsm_write_spec`) and TypeScript
(`setLsmWriteSpec` with `specType` `"bucket"` / `"identity"` /
`"unsharded"`). `RemoteTable` returns `NotSupported`.
The actual `merge_insert` LSM dispatch and `ShardWriter` write path are
a
follow-up — this PR only installs and clears the spec.
## Summary
Adds `Table::set_unenforced_primary_key` — records a single column as
the
table's unenforced primary key in Lance schema field metadata.
"Unenforced"
means LanceDB does not check uniqueness on write; the key is metadata
that
`merge_insert` consumes.
- Single-column only; the column must exist and have a supported dtype
(Int32, Int64, Utf8, LargeUtf8, Binary, LargeBinary, FixedSizeBinary).
The
API accepts an iterable for binding ergonomics but requires exactly one
column — compound keys are rejected.
- The primary key is immutable: calling this on a table that already has
an
unenforced primary key is rejected. Concurrent writers racing to set the
key
fail at commit time rather than silently overriding it.
- `RemoteTable` returns `NotSupported`.
- Bindings: Python (`AsyncTable`, `LanceTable`, `RemoteTable`) and
TypeScript
(`Table.setUnenforcedPrimaryKey`).
## Context
Split out from #3354 per review feedback, so the unenforced primary key
and the
`merge_insert` sharding spec land as separate reviewable PRs.
No Lance dependency bump — `main` is already on v7.0.0-beta.10, which
includes
the field-metadata round-trip fix the API relies on. Enforcing
primary-key
immutability at the Lance commit layer (so the cross-column concurrent
race is
also rejected) is a companion Lance change: lance-format/lance#6810.
## Summary
PyTorch's `DataLoader` uses fork-based multiprocessing by default on
Linux, but threads do not survive `fork()`. LanceDB's Python bindings
drive async work through two threaded layers, both of which become inert
in a forked child:
- `BackgroundEventLoop` runs an asyncio loop on a Python
`threading.Thread`.
- `pyo3-async-runtimes::tokio` holds a global multi-threaded tokio
runtime whose worker threads also die on fork — and its runtime lives in
a `OnceLock` that cannot be replaced after first use.
As a result, any `Permutation` (or other async API) used inside a
fork-based `DataLoader` worker hangs indefinitely. This PR makes both
layers fork-safe so `Permutation` works as a `torch.utils.data.Dataset`
with `num_workers > 0`.
## Approach
### Rust — new `python/src/runtime.rs`
Mirrors the pattern used in [Lance's Python
bindings](456198cd6f/python/src/lib.rs (L139)),
adapted for the async-bridge use case.
- `LanceRuntime` implements `pyo3_async_runtimes::generic::Runtime +
ContextExt`, backed by an `AtomicPtr<tokio::runtime::Runtime>` we own
(sidestepping `pyo3-async-runtimes`'s frozen `OnceLock` global).
- A `pthread_atfork(after_in_child)` handler nulls the pointer; the next
`spawn` rebuilds the runtime in the child. The previous runtime is
intentionally **leaked** — calling `Drop` would try to join now-dead
worker threads and hang.
- `runtime::future_into_py` is a drop-in for
`pyo3_async_runtimes::tokio::future_into_py`. All ~80 call sites in
`arrow.rs` / `connection.rs` / `permutation.rs` / `query.rs` /
`table.rs` are updated to route through it.
- `python/Cargo.toml` adds `libc = "0.2"` and the tokio
`rt-multi-thread` feature.
### Python — `lancedb/background_loop.py`
- Refactors `BackgroundEventLoop.__init__` to a reusable `_start()`
method.
- An `os.register_at_fork(after_in_child=…)` hook calls `LOOP._start()`
to give the singleton a fresh asyncio loop and thread **in place**. This
matters because the rest of the codebase imports `LOOP` via `from
.background_loop import LOOP` — rebinding the module attribute would
leave those references holding the dead loop.
### Python — `lancedb/__init__.py`
Removes the `__warn_on_fork` pre-fork warning (and the now-unused
`import warnings`). Fork is supported.
## Test plan
- [x] New `test_permutation_dataloader_fork_workers` in
`python/tests/test_torch.py`: runs a `Permutation` through
`torch.utils.data.DataLoader(num_workers=2,
multiprocessing_context="fork")` inside a spawn-isolated child with a
30s hang detector. **Pre-fix**: timed out at 36s. **Post-fix**: passes
in ~3.6s.
- [x] New `test_remote_connection_after_fork` in
`python/tests/test_remote_db.py`: forks a child that creates a fresh
`lancedb.connect(...)` against a mock HTTP server and calls
`table_names()`; passes in <1s, validates the runtime reset is
sufficient for fresh remote clients.
- [x] All 62 tests in `test_torch.py` + `test_permutation.py` pass.
- [x] All 35 tests in `test_remote_db.py` pass.
- [x] `test_table.py` (87) + `test_db.py` + `test_query.py` (157, minus
one unrelated `sentence_transformers` import skip) — 244 passing.
- [x] `cargo clippy -p lancedb-python --tests` clean.
- [x] `cargo fmt`, `ruff check`, `ruff format` all clean.
## Known limitation (follow-up)
This PR makes a **freshly-built** `lancedb.connect(...)` work in a
forked child. An **inherited** `Connection` from the parent still
carries an inherited `reqwest::Client` whose hyper connection pool
references socket FDs and TCP/TLS state shared with the parent — using
it from the child after fork is unsafe (especially with HTTP/1.1
keep-alive). The recommended pattern for fork-based `DataLoader` workers
that hit a remote DB is to construct a new connection inside the worker.
Auto-clearing inherited HTTP client pools on fork would require tracking
live `Connection` instances in `lancedb` core and is left for a
follow-up PR.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
## Summary
Adds progress reporting for `table.add()` so users can track large write
operations. The progress callback is available in Rust, Python (sync and
async), and through the PyO3 bindings.
### Usage
Pass `progress=True` to get an automatic tqdm bar:
```python
table.add(data, progress=True)
# 100%|██████████| 1000000/1000000 [00:12<00:00, 82345 rows/s, 45.2 MB/s | 4/4 workers]
```
Or pass a tqdm bar for more control:
```python
from tqdm import tqdm
with tqdm(unit=" rows") as pbar:
table.add(data, progress=pbar)
```
Or use a callback for custom progress handling:
```python
def on_progress(p):
print(f"{p['output_rows']}/{p['total_rows']} rows, "
f"{p['active_tasks']}/{p['total_tasks']} workers, "
f"done={p['done']}")
table.add(data, progress=on_progress)
```
In Rust:
```rust
table.add(data)
.progress(|p| println!("{}/{:?} rows", p.output_rows(), p.total_rows()))
.execute()
.await?;
```
### Details
- `WriteProgress` struct in Rust with getters for `elapsed`,
`output_rows`, `output_bytes`, `total_rows`, `active_tasks`,
`total_tasks`, and `done`. Fields are private behind getters so new
fields can be added without breaking changes.
- `WriteProgressTracker` tracks progress across parallel write tasks
using a mutex for row/byte counts and atomics for active task counts.
- Active task tracking uses an RAII guard pattern (`ActiveTaskGuard`)
that increments on creation and decrements on drop.
- For remote writes, `output_bytes` reflects IPC wire bytes rather than
in-memory Arrow size. For local writes it uses in-memory Arrow size as a
proxy (see TODO below).
- tqdm postfix displays throughput (MB/s) and worker utilization
(active/total).
- The `done` callback always fires, even on error (via `FinishOnDrop`),
so progress bars are always finalized.
### TODO
- Track actual bytes written to disk for local tables. This requires
Lance to expose a progress callback from its write path. See
lance-format/lance#6247.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
## Summary
- Implement `RemoteTable.prewarm_data(columns)` calling `POST
/v1/table/{id}/page_cache/prewarm/`
- Implement `RemoteTable.prewarm_index(name)` calling `POST
/v1/table/{id}/index/{name}/prewarm/` (previously returned
`NotSupported`)
- Add `BaseTable::prewarm_data(columns)` trait method and `Table` public
API in Rust core
- Add PyO3 bindings and Python API (`AsyncTable`, `LanceTable`,
`RemoteTable`) for `prewarm_data`
- Add type stubs for `prewarm_index` and `prewarm_data` in
`_lancedb.pyi`
- Upgrade Lance to 3.0.0-rc.3 with breaking change fixes
Co-authored-by: Will Jones <willjones127@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR migrates all Rust crates in the workspace to Rust 2024 edition
and addresses the resulting compatibility updates. It also fixes all
clippy warnings surfaced by the workspace checks so the codebase remains
warning-free under the current lint configuration.
Context:
- Scope: workspace edition bump (`2021` -> `2024`) plus follow-up
refactors required by new edition and clippy rules.
- Validation: `cargo fmt --all` and `cargo clippy --quiet --features
remote --tests --examples -- -D warnings` both pass.
This hooks up a new writer implementation for the `add()` method. The
main immediate benefit is it allows streaming requests to remote tables,
and at the same time allowing retries for most inputs.
In NodeJS, we always convert the data to `Vec<RecordBatch>`, so it's
always retry-able.
For Python, all are retry-able, except `Iterator` and
`pa.RecordBatchReader`, which can only be consumed once. Some, like
`pa.datasets.Dataset` are retry-able *and* streaming.
A lot of the changes here are to make the new DataFusion write pipeline
maintain the same behavior as the existing Python-based preprocessing,
such as:
* casting input data to target schema
* rejecting NaN values if `on_bad_vectors="error"`
* applying embedding functions.
In future PRs, we'll enhance these by moving the embedding calls into
DataFusion and making sure we parallelize them. See:
https://github.com/lancedb/lancedb/issues/3048
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
BREAKING CHANGE: Arbitrary `impl RecordBatchReader` is no longer
accepted, it must be made into `Box<dyn RecordBatchReader>`.
This PR replaces `IntoArrow` with a new trait `Scannable` to define
input row data. This provides the following advantages:
1. **We can implement `Scannable` for more types than `IntoArrow`, such
as `RecordBatch` and `Vec<RecordBatch>`.** The `IntoArrow` trait was
implemented for arbitrary `T: RecordBatchReader`, and the Rust compiler
would prevent us from implementing it for foreign types like
`RecordBatch` because (theoretically) those types might implement
`RecordBatchReader` in the future. That's why we implement `Scannable`
for `Box<dyn RecordBatchReader>` instead; since it's a concrete type it
doesn't block implementing for other foreign types.
2. **We can potentially replay `Scannable` values**. Previously, we had
to choose between buffering all data in memory and supporting retries of
writes. But because `Scannable` things can optionally support
re-scanning, we now have a way of supporting retries while also
streaming.
3. **`Scannable` can provide hints like `num_rows`, which can be used to
schedule parallel writers.** Without knowing the total number of rows,
it's difficult to know whether it's worth writing multiple files in
parallel.
We don't yet fully take advantage of (2) and (3) yet, but will in future
PRs. For (2), in order to be ready to leverage this, we need to hook the
`Scannable` implementation up to Python and NodeJS bindings. Right now
they always pass down a stream, but we want to make sure they support
retries when possible. And for (3), this will need to be hooked up to
#2939 and to a pipeline for running pre-processing steps (like embedding
generation).
## Other changes
* Moved `create_table` and `add_data` into their own modules. I've
created a follow up issue to split up `table.rs` further, as it's by far
the largest file: https://github.com/lancedb/lancedb/issues/2949
* Eliminated the `HAS_DATA` generic for `CreateTableBuilder`. I didn't
see any public-facing places where we differentiated methods, which is
why I felt this simplification was okay.
* Added an `Error::External` variant and integrated some conversions to
allow certain errors to pass through transparently. This will fully work
once we upgrade Lance and get to take advantage of changes in
https://github.com/lance-format/lance/pull/5606
* Added LZ4 compression support for write requests to remote endpoints.
I checked and this has been supported on the server for > 1 year.
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Expose `initial_storage_options()` and `latest_storage_options()` in
lance Dataset, in lancedb rust, python and typescript SDKs.
---------
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
This pipes the num_attempts field from lance's merge insert result
through lancedb. This allows callers of merge_insert to get a better
idea of whether transaction conflicts are occurring.
I'm working on a lancedb version of pytorch data loading (and hopefully
addressing https://github.com/lancedb/lance/issues/3727).
However, rather than rely on pytorch for everything I'm moving some of
the things that pytorch does into rust. This gives us more control over
data loading (e.g. using shards or a hash-based split) and it allows
permutations to be persistent. In particular I hope to be able to:
* Create a persistent permutation
* This permutation can handle splits, filtering, shuffling, and sharding
* Create a rust data loader that can read a permutation (one or more
splits), or a subset of a permutation (for DDP)
* Create a python data loader that delegates to the rust data loader
Eventually create integrations for other data loading libraries,
including rust & node
Enables two new parameters when building indices:
* `name`: Allows explicitly setting a name on the index. Default is
`{col_name}_idx`.
* `train` (default `True`): When set to `False`, an empty index will be
immediately created.
The upgrade of Lance means there are also additional behaviors from
cd76a993b8:
* When a scalar index is created on a Table, it will be kept around even
if all rows are deleted or updated.
* Scalar indices can be created on empty tables. They will default to
`train=False` if the table is empty.
---------
Co-authored-by: Weston Pace <weston.pace@gmail.com>
These operations have existed in lance for a long while and many users
need to drop down to lance for this capability. This PR adds the API and
implements it using filters (e.g. `_rowid IN (...)`) so that in doesn't
currently add any load to `BaseTable`. I'm not sure that is sustainable
as base table implementations may want to specialize how they handle
this method. However, I figure it is a good starting point.
In addition, unlike Lance, this API does not currently guarantee
anything about the order of the take results. This is necessary for the
fallback filter approach to work (SQL filters cannot guarantee result
order)
Provides the ability to set a timeout for merge insert. The default
underlying timeout is however long the first attempt takes, or if there
are multiple attempts, 30 seconds. This has two use cases:
1. Make the timeout shorter, when you want to fail if it takes too long.
2. Allow taking more time to do retries.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Added support for specifying a timeout when performing merge insert
operations in Python, Node.js, and Rust APIs.
- Introduced a new option to control the maximum allowed execution time
for merge inserts, including retry timeout handling.
- **Documentation**
- Updated and added documentation to describe the new timeout option and
its usage in APIs.
- **Tests**
- Added and updated tests to verify correct timeout behavior during
merge insert operations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
add restore with tag API in python and nodejs API and add tests to guard
them
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- The restore functionality now supports using version tags in addition
to numeric version identifiers, allowing you to revert tables to a state
marked by a tag.
- **Bug Fixes**
- Restoring with an unknown tag now properly raises an error.
- **Documentation**
- Updated documentation and examples to clarify that restore accepts
both version numbers and tags.
- **Tests**
- Added new tests to verify restore behavior with version tags and error
handling for unknown tags.
- Added tests for checkout and restore operations involving tags.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
return version info for all write operations (add, update, merge_insert
and column modification operations)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Table modification operations (add, update, delete, merge,
add/alter/drop columns) now return detailed result objects including
version numbers and operation statistics.
- Result objects provide clearer feedback such as rows affected and new
table version after each operation.
- **Documentation**
- Updated documentation to describe new result objects and their fields
for all relevant table operations.
- Added documentation for new result interfaces and updated method
return types in Node.js and Python APIs.
- **Tests**
- Enhanced test coverage to assert correctness of returned versioning
and operation metadata after table modifications.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Based on this comment:
https://github.com/lancedb/lancedb/issues/2228#issuecomment-2730463075
and https://github.com/lancedb/lance/pull/2357
Here is my attempt at implementing bindings for returning merge stats
from a `merge_insert.execute` call for lancedb.
Note: I have almost no idea what I am doing in Rust but tried to follow
existing code patterns and pay attention to compiler hints.
- The change in nodejs binding appeared to be necessary to get
compilation to work, presumably this could actual work properly by
returning some kind of NAPI JS object of the stats data?
- I am unsure of what to do with the remote/table.rs changes -
necessarily for compilation to work; I assume this is related to LanceDB
cloud, but unsure the best way to handle that at this point.
Proof of function:
```python
import pandas as pd
import lancedb
db = lancedb.connect("/tmp/test.db")
test_data = pd.DataFrame(
{
"title": ["Hello", "Test Document", "Example", "Data Sample", "Last One"],
"id": [1, 2, 3, 4, 5],
"content": [
"World",
"This is a test",
"Another example",
"More test data",
"Final entry",
],
}
)
table = db.create_table("documents", data=test_data, exist_ok=True, mode="overwrite")
update_data = pd.DataFrame(
{
"title": [
"Hello, World",
"Test Document, it's good",
"Example",
"Data Sample",
"Last One",
"New One",
],
"id": [1, 2, 3, 4, 5, 6],
"content": [
"World",
"This is a test",
"Another example",
"More test data",
"Final entry",
"New content",
],
}
)
stats = (
table.merge_insert(on="id")
.when_matched_update_all()
.when_not_matched_insert_all()
.execute(update_data)
)
print(stats)
```
returns
```
{'num_inserted_rows': 1, 'num_updated_rows': 5, 'num_deleted_rows': 0}
```
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
## Summary by CodeRabbit
- **New Features**
- Merge-insert operations now return detailed statistics, including
counts of inserted, updated, and deleted rows.
- **Bug Fixes**
- Tests updated to validate returned merge-insert statistics for
accuracy.
- **Documentation**
- Method documentation improved to reflect new return values and clarify
merge operation results.
- Added documentation for the new `MergeStats` interface detailing
operation statistics.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Co-authored-by: Will Jones <willjones127@gmail.com>
* Add a new "table stats" API to expose basic table and fragment
statistics with local and remote table implementations
### Questions
* This is using `calculate_data_stats` to determine total bytes in the
table. This seems like a potentially expensive operation - are there any
concerns about performance for large datasets?
### Notes
* bytes_on_disk seems to be stored at the column level but there does
not seem to be a way to easily calculate total bytes per fragment. This
may need to be added in lance before we can support fragment size
(bytes) statistics.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Added a method to retrieve comprehensive table statistics, including
total rows, index counts, storage size, and detailed fragment size
metrics such as minimum, maximum, mean, and percentiles.
- Enabled fetching of table statistics from remote sources through
asynchronous requests.
- Extended table interfaces across Python, Rust, and Node.js to support
synchronous and asynchronous retrieval of table statistics.
- **Tests**
- Introduced tests to verify the accuracy of the new table statistics
feature for both populated and empty tables.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
add the tag related API to list existing tags, attach tag to a version,
update the tag version, delete tag, get the version of the tag, and
checkout the version that the tag bounded to.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Introduced table version tagging, allowing users to create, update,
delete, and list human-readable tags for specific table versions.
- Enabled checking out a table by either version number or tag name.
- Added new interfaces for tag management in both Python and Node.js
APIs, supporting synchronous and asynchronous workflows.
- **Bug Fixes**
- None.
- **Documentation**
- Updated documentation to describe the new tagging features, including
usage examples.
- **Tests**
- Added comprehensive tests for tag creation, updating, deletion,
listing, and version checkout by tag in both Python and Node.js
environments.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
* Add new wait_for_index() table operation that polls until indices are
created/fully indexed
* Add an optional wait timeout parameter to all create_index operations
* Python and NodeJS interfaces
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
## Summary by CodeRabbit
- **New Features**
- Added optional waiting for index creation completion with configurable
timeout.
- Introduced methods to poll and wait for indices to be fully built
across sync and async tables.
- Extended index creation APIs to accept a wait timeout parameter.
- **Bug Fixes**
- Added a new timeout error variant for improved error reporting on
index operations.
- **Tests**
- Added tests covering successful index readiness waiting, timeout
scenarios, and missing index cases.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Added the ability to prewarm (load into memory) table indexes via new
methods in Python, Node.js, and Rust APIs, potentially reducing
cold-start query latency.
- **Bug Fixes**
- Ensured prewarming an index does not interfere with subsequent search
operations.
- **Tests**
- Introduced new test cases to verify full-text search index creation,
prewarming, and search functionalities in both Python and Node.js.
- **Chores**
- Updated dependencies for improved compatibility and performance.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Co-authored-by: Lu Qiu <luqiujob@gmail.com>
- adds `loss` into the index stats for vector index
- now `optimize` can retrain the vector index
---------
Signed-off-by: BubbleCal <bubble-cal@outlook.com>
### Changes to sync API
* Updated `LanceTable` and `LanceDBConnection` reprs
* Add `storage_options`, `data_storage_version`, and
`enable_v2_manifest_paths` to sync create table API.
* Add `storage_options` to `open_table` in sync API.
* Add `list_indices()` and `index_stats()` to sync API
* `create_table()` will now create only 1 version when data is passed.
Previously it would always create two versions: 1 to create an empty
table and 1 to add data to it.
### Changes to async API
* Add `embedding_functions` to async `create_table()` API.
* Added `head()` to async API
### Refactors
* Refactor index parameters into dataclasses so they are easier to use
from Python
* Moved most tests to use an in-memory DB so we don't need to create so
many temp directories
Closes#1792Closes#1932
---------
Co-authored-by: Weston Pace <weston.pace@gmail.com>
BREAKING CHANGE: the return value of `index_stats` method has changed
and all `index_stats` APIs now take index name instead of UUID. Also
several deprecated index statistics methods were removed.
* Removes deprecated methods for individual index statistics
* Aligns public `IndexStatistics` struct with API response from LanceDB
Cloud.
* Implements `index_stats` for remote Rust SDK and Python async API.
The new V2 manifest path scheme makes discovering the latest version of
a table constant time on object stores, regardless of the number of
versions in the table. See benchmarks in the PR here:
https://github.com/lancedb/lance/pull/2798Closes#1583
