The write path these APIs drive is Lance's MemWAL, and "LSM" described
its shape rather than naming it. The surface now says MemWAL, and turning
it on and off reads as enabling a feature rather than installing a spec.
| Before | After |
|---|---|
| `set_lsm_write_spec` | `enable_memwal` |
| `unset_lsm_write_spec` | `disable_memwal` |
| `get_lsm_write_spec` | `get_memwal_spec` |
| `flush_lsm` / `compact_lsm` / `checkpoint_lsm` | `flush_memwal` / `compact_memwal` / `checkpoint_memwal` |
| `get_lsm_stats` | `get_memwal_stats` |
| `close_lsm_writers` | `close_memwal_writers` |
| `use_lsm` (query, merge insert) | `use_memwal` |
| `LsmWriteSpec` / `LsmStats` | `MemWalWriteSpec` / `MemWalStats` |
| Java `LanceDbTableLsm` | `LanceDbTableMemWal` |
TypeScript and Java use camelCase (`enableMemWal`, `getMemWalStats`,
...); the napi methods set `js_name` so the generated names keep the
`MemWal` casing. The flush/compact/checkpoint methods keep a `_memwal`
suffix so `compact_memwal` is not confused with `compact_files` and
`optimize`, which compact the base table.
## Wire
The remote routes and JSON envelopes move with the SDKs and must ship
together with the matching server change:
- `/set_lsm_write_spec/` -> `/enable_memwal/`, `/unset_lsm_write_spec/`
-> `/disable_memwal/`, `/get_lsm_write_spec/` -> `/get_memwal_spec/`,
`/flush_lsm/`, `/compact_lsm/`, `/get_lsm_stats/` -> `*_memwal/`
- response keys `lsm_write_spec` -> `memwal_spec`, `lsm_stats` ->
`memwal_stats`; query and merge-insert body field `use_lsm` ->
`use_memwal`
## Also fixed
The previous rename turned the Java `bucket` sharding mode into
`tableShard` in the javadoc example and tests, and the test fixtures
sent `tableShards` where the parser reads `table_shards`, so the Java
tests did not compile. Both are restored.
Internal names (`LsmMode`, `LsmScanner`, the `merge::lsm` and
`query::lsm` modules) are unchanged.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Empty local TypeScript queries returned a zero-row Arrow table with no
columns because `toArrow()` built the table solely from record batches.
Local streams can yield no batches, while remote streams often supply an
empty batch carrying the schema.
Expose the executed stream's schema through the native iterator and
decode it into an empty Arrow table when no batches arrive. This
preserves projected and search columns, types, nullability, and metadata
without executing another query. Document the empty-result behavior.
Validation:
- Eleven regression cases failed with the original `toArrow()`
implementation; all twelve now pass, including remote schema-only and
empty-batch responses.
- All 1,075 tests in the query, remote, Arrow, and table suites pass.
- Native build, TypeScript compilation, Rust formatting and Clippy (`-D
warnings`), TypeScript lint/formatting, and documentation generation
pass.
Fixes#4386
<!-- lance-gatekeeper-fix:v1 agent=7d589da1f7db5c7383f9600490e111a9
generation=1 -->
Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>
Thanks @vincentkoc for starting this! I was just looking into this
myself. I started with your PR and added:
- make arrow 21 the default
- widen the peer range to <22 so if they release 21.3 that'll be
included
- have to do skipLibCheck in tsconfig.json, because of flatbuffers 25
which needs TypeScript 5.7
- fix override in Symbol.hasInstance
- support new types in Arrow 20-21 (LargeList, Utf8View, BinaryView,
IntervalMonthDayNano)
- arrow-compat job in nodejs.yml that runs tests with arrow 19 and 20
(adds 2 sec)
- put the list of arrow types in one place
- update NODEJS_THIRD_PARTY_LICENSES.md
- regenerated typescript docs (sorry about reorderings, one time cost)
- reformat arrow.test.ts (sorry, almost all whitespace, thanks to biome.
git diff -w shows 110 lines edited)
- fixed Sliced Utf8View / BinaryView serialization error, by just
converting them to Utf8 and Binary (as our rust code would anyway)
---------
Co-authored-by: Vincent Koc <vincentkoc@ieee.org>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
## 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`.
Adds client-side support for analyze_plan distributed metrics modes
across Rust, Python, and TypeScript clients. Defaults to aggregate for
backward compatibility and sends the remote distributed_metrics
parameter only when a non-default mode is requested.
JS native Async Generator, more efficient asynchronous iteration, fewer
synthetic promises, and the ability to handle `catch` or `break` of
parent loop in `finally` block
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)
Daniel RammerandClaude Opus 5.5
lancedb-gatefixer[bot]
Heng Ge
Jack Ye
S.A.N
Weston Pace