## What
MemWAL LSM **read** support. When a table has an LSM write spec
(`set_lsm_write_spec`), `merge_insert` upserts live in the MemWAL
active/frozen memtables and flushed SSTables until an external
compaction merges them into the base table, so a normal scan returns
**stale** data. This routes reads through Lance's `LsmScanner` so
queries also surface that in-flight data, deduplicated by primary key
(newest generation wins).
## How
- Adds a **`use_lsm: Option<bool>`** query flag, symmetric with the
`merge_insert` flag:
- **unset** — auto-route through the LSM scanner when the table carries
a write spec
- **`use_lsm(true)`** — force the LSM path; error if there is no spec
- **`use_lsm(false)`** — read the base table only (the escape hatch)
- Plain scan, single-column full-text search, and single-vector ANN all
run through one `LsmScanner` (assembled from on-disk shard manifests
plus the cached writer's in-memory memtables), so a `where` predicate is
honored as a **prefilter** uniformly — including for vector search.
- **Compaction-aware snapshots:** an SSTable generation is dropped only
once it is both compacted into the base table and covered by the arm's
base-index catch-up (`index_catchup`); plain scans use the compaction
watermark alone.
- Query shapes the scanner cannot honor hard-error with guidance to set
`use_lsm(false)`: hybrid, multi/binary vectors, `with_row_id`,
reranking, `order_by`, dynamic/Substrait projection or filters,
`distance_range`, `use_index(false)`, postfilter, take-by-row-id/offset,
reads from a time-traveled version, and an unmaintained or ambiguous
(multiple) FTS/vector index. Namespace-pushdown queries fall back to
local execution when a spec is present; WAL-only writers are handled.
- Exposed across the Rust core and the Python (`use_lsm`) and TypeScript
(`useLsm`) bindings, including `TakeQuery`.
Rebased from Lance `7.2.0-beta.3` to `10.0.0-beta.3`.
## Summary
When an `LsmWriteSpec` is installed on a table (#3396), `merge_insert`
upsert
calls are dispatched through Lance's MemWAL `ShardWriter` (LSM-style
append)
instead of the standard merge path.
- **`use_lsm_write`** — a `merge_insert` builder option, default `true`;
set it
`false` to use the standard path for a call even when a spec is set.
- **`assume_pre_sharded`** — a `merge_insert` builder option, default
`false`;
skips the per-row shard check and routes by the first row only.
- **`close_lsm_writers`** — drains and closes the table's cached MemWAL
shard
writers.
- The `merge_insert` **`on`** columns default to, and are validated
against,
the table's unenforced primary key.
- Shard writers are cached alongside the dataset (in
`DatasetConsistencyWrapper`) and reused for the session.
- `MergeResult` gains **`num_rows`** — on the LSM path the insert/update
breakdown is unknown until compaction, so only the total is reported.
Routing covers all three sharding strategies — bucket (murmur3,
Iceberg-compatible), identity, and unsharded. Each `merge_insert` call
targets
a single shard; the whole input is collected and validated before a
single
atomic `ShardWriter::put`, so a validation failure leaves the MemWAL
untouched.
Bindings: Python (`merge_insert(...).use_lsm_write(...)` /
`.assume_pre_sharded(...)`, `Table.close_lsm_writers`) and TypeScript
(`mergeInsert(...).useLsmWrite(...)` / `.assumePreSharded(...)`,
`Table.closeLsmWriters`).
## Context
Reconstructed from the original #3354 branch onto current `main`: the
branch
predated the #3394 (unenforced primary key) / #3396 (`LsmWriteSpec`)
split and
has been rebuilt on that merged foundation. Depends on Lance
`v7.0.0-beta.13`.
The MemWAL read path (reading un-flushed shard data back into queries)
and
remote (LanceDB Cloud) LSM support are follow-ups.
---------
Co-authored-by: Jack Ye <yezhaoqin@gmail.com>
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 -->
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>
* Make `npm run docs` fail if there are any warnings. This will catch
items missing from the API reference.
* Add a check in our CI to make sure `npm run dos` runs without warnings
and doesn't generate any new files (indicating it might be out-of-date.
* Hide constructors that aren't user facing.
* Remove unused enum `WriteMode`.
Closes#2068
Heng Ge
Will Jones
LuQQiu
Alex Pilon