u70b3 commented on issue #66497:
URL: https://github.com/apache/doris/issues/66497#issuecomment-5194018594
here is my design proposal for this issue. It builds on #65730 (merged), the
Lance Java SDK / lance-c APIs already
pinned in the repo, and two precedent studies: how Doris implements
mutations for other external catalogs (Iceberg/Hive/Paimon), and lance-spark's
index
DDL (the only landed cross-engine precedent). Open questions are numbered
at the end. /cc @Gabriel39 @zhangstar333
## 1. SQL surface
Reuse the existing index DDL grammar (`createIndex` / `dropIndex` /
`showIndex` in `DorisParser.g4`), extended to accept Lance external tables:
```sql
-- Vector index
CREATE INDEX [IF NOT EXISTS] idx ON lance_ctl.db.tbl (vec_col)
USING IVF_PQ PROPERTIES ("nlist" = "256", "metric" = "l2");
-- Scalar indexes
CREATE INDEX idx ON lance_ctl.db.tbl (col) USING BTREE; -- or BITMAP /
INVERTED
-- Replace / rebuild with the same name (atomic swap via Lance
replace=true)
CREATE OR REPLACE INDEX idx ON lance_ctl.db.tbl (vec_col) USING IVF_PQ;
-- Inspect
SHOW INDEX FROM lance_ctl.db.tbl;
DROP INDEX [IF EXISTS] idx ON lance_ctl.db.tbl;
```
Notes:
- `USING`: extend the enum with Lance concrete types. Vector: `IVF_FLAT |
IVF_SQ | IVF_PQ | IVF_HNSW_FLAT | IVF_HNSW_SQ | IVF_HNSW_PQ`; scalar: `BTREE |
BITMAP | INVERTED` (matching lance-c's `LanceVectorIndexType` /
`LanceScalarIndexType` and the #66340 matrix). PROPERTIES map to Lance
`IndexParams`
(`nlist`, `metric`, ...).
- Same-name semantics follow the Lance SDK's safe default: `CREATE INDEX`
fails if the name already exists; `IF NOT EXISTS` no-ops; `CREATE OR REPLACE
INDEX` maps to Lance `replace=true`, an atomic swap in a single commit.
This keeps lance-spark's replace capability in Doris's explicit style. (Q3)
- `SHOW INDEX` output columns for Lance tables: `Name | Column | Type |
UUID | DatasetVersion | IndexedFragments | UnindexedFragments` — covering the
issue's required "names, UUIDs, columns, types, dataset versions" plus
lance-spark-style coverage stats (backed by `listIndexes` /
`lance_dataset_index_list_json`).
- The number of indexes on a table is the row count of `SHOW INDEX`
(backed by `listIndexes().size()` / `lance_dataset_index_count`); no separate
statement is proposed.
- Index names are case-insensitive and stored lowercase, following Lance /
lance-spark convention.
- Single-column indexes only in the initial implementation.
## 2. Where index operations execute (Q1)
Precedent study: every mutable external catalog in Doris performs
metadata-level mutations inside the FE via an embedded SDK —
`IcebergMetadataOps`,
`HiveMetadataOps`, `PaimonMetadataOps`, `MaxComputeMetadataOps` all
implement the shared `ExternalMetadataOps` interface; a null `metadataOps` means
read-only (JDBC is the read-only example). BE never touches the external
system's metadata. `LanceExternalCatalog` currently has no metadataOps (=
read-only), so the conventional extension point is FE-side index methods
calling the Lance Java SDK.
**Proposal for the initial implementation — FE via Lance Java SDK (JNI).**
`createIndex` / `dropIndex` / `listIndexes` all exist in the pinned lance-core
9.1.0-beta.3. No thrift / RPC / BE changes; follows the
`ExternalMetadataOps` convention.
One honest caveat: unlike a pure metadata mutation, Lance index creation
bundles data-plane compute (column scan + IVF training) into a single monolithic
Rust call, so with this approach that compute runs in native threads
inside the FE process. Lance does expose the primitives for a distributed build
—
per-fragment segment building without commit, then a coordinator commit
(`create_index_uncommitted` / `commitExistingIndexSegments`; lance-spark's
`num_segments` mode uses this). A follow-up could offload building to BE
(the pinned lance-c v0.1.2 already ships the matching Phase-2 C APIs) while FE
keeps initiation and commit, mirroring the Iceberg INSERT pattern. The
initial implementation stays FE-only behind a `LanceIndexOperator` interface so
the later swap does not change SQL semantics.
## 3. Synchronous execution (Q2)
Proposal: synchronous DDL for the initial implementation. Precedents line
up: Doris's internal light `CREATE INDEX` is a synchronous metadata change; the
async `BUILD INDEX` framework (`IndexChangeJob` per partition) is bound to
Doris's tablet / replica / BE-agent model and does not transfer to Lance;
lance-spark's `CREATE INDEX` is synchronous as well.
Semantics: killing the statement before commit leaves nothing persisted
(Lance commits atomically at the end), so interruption is safe. Documentation
will note that build time scales with dataset size. Follow-up candidates:
an async job with progress reporting (the Lance SDK exposes
`IndexBuildProgress`), and/or the REST namespace's native async model.
## 4. Authorization
- `CREATE / CREATE OR REPLACE / DROP INDEX` → `ALTER_PRIV` on the target
table. Matches both precedents: internal CREATE/DROP/BUILD INDEX share a single
ALTER check (`AlterTableCommand.validate`), and external-table ALTER
operations (Iceberg branch/tag, add/drop column) check `ALTER_PRIV`.
- `SHOW INDEX` → `SHOW_PRIV` on the table, matching internal SHOW INDEX.
Stated as design rather than an open question since both precedents agree
— reviewers please flag if you disagree.
## 5. Lifecycle semantics (the "define semantics" scope item)
These follow Lance's transaction semantics directly (see
`docs/src/format/table/transaction.md` in lance-format/lance); Doris does not
invent its own:
- **Versioning**: every CREATE / OR REPLACE / DROP is one Lance
transaction producing a new dataset version with an atomic metadata switch. A
failed or
interrupted build commits nothing — no partial index is ever visible.
- **Concurrency**: in-flight queries are unaffected (#65730 pins the
dataset version at planning time). Two concurrent creations with the same name:
last
committer wins. Index builds are compatible with concurrent appends (new
fragments are simply uncovered); they conflict with overwrite/restore, surfaced
as a retryable error.
- **Failure recovery**: FE crash after commit but before responding → the
index exists; the user verifies via `SHOW INDEX`. `IF NOT EXISTS` / `OR
REPLACE` make retries idempotent. `DROP` on a missing name errors unless
`IF EXISTS`.
- **DROP semantics**: DROP only removes the index from the manifest;
physical index files are reclaimed later by Lance cleanup / VACUUM, so time
travel
is preserved.
- **Metadata refresh**: after a successful mutation, FE invalidates the
table's cached metadata through the existing `RefreshManager` /
`ExtMetaCacheMgr`
mechanism (same as Iceberg DDL). `SHOW INDEX` always reads live from the
dataset at its latest version, never from the catalog cache.
## 6. Scope of the initial implementation
- Vector: `IVF_PQ` and `IVF_FLAT` verified end-to-end (what the #65730
query path consumes); other types accepted syntactically but gated to what tests
cover.
- Scalar: `BTREE`, `BITMAP`, `INVERTED`.
- Catalogs: filesystem (local / file / s3). **REST Namespace: reject with
a clear error.** The REST spec does define v1 index endpoints, but they are
asynchronous (transactionId + status polling), optional for servers to
implement, and have no replace field — a poor fit for the synchronous,
atomic-replace semantics proposed here. (Q4)
- Tests: FE UTs (parse / analyze / privilege / catalog API), regression
tests (create → show → or-replace → drop → failure paths, vector + scalar), docs
PR in apache/doris-website.
## 7. Implementation approach (orientation; details in the PR)
- Reuse the existing command chain rather than adding Lance-specific
statements: CREATE/DROP INDEX already parse into `AlterTableCommand` + ops; SHOW
INDEX into `ShowIndexCommand`. The change is to admit `LanceExternalTable`
at the existing gates (external-table op whitelist, `Alter` dispatch switch,
`ShowIndexCommand` table-type branch) — the same pattern Iceberg
branch/tag support used.
- Catalog side: add index methods (`createIndex` / `dropIndex` /
`listIndexes`) to `LanceExternalCatalog`, calling the Lance Java SDK at the
dataset's
latest version.
- Estimated size: ~2.5k lines including FE UTs and regression tests.
## 8. Coverage of the issue checklist
- **Scope**: create vector / scalar indexes → §1; show the number of
indexes → row count of `SHOW INDEX` (§1); show names / UUIDs / columns / types /
dataset versions → `SHOW INDEX` columns (§1); replace or rebuild with the
same name → `CREATE OR REPLACE INDEX` (§1, Q3); drop by name → `DROP INDEX`
(§1); authorization / concurrency / versioning / failure recovery /
metadata refresh semantics → §4–5.
- **Completion criteria**: FE statements and metadata APIs → §7;
service-side index operations integrated with Lance → §2; unit and regression
tests →
§6; user documentation → §6; verified for vector and scalar index types →
§6.
## Questions for reviewers
- **Q1**: FE-only (Java SDK) for the initial implementation, with the
BE-distributed fragment build as an explicit follow-up path — OK?
- **Q2**: Synchronous DDL initially (no SHOW/CANCEL BUILD INDEX
integration for Lance) — OK?
- **Q3**: Is extending the grammar with `CREATE OR REPLACE INDEX`
acceptable? (Alternative: `PROPERTIES("replace"="true")` — avoids a grammar
change but
hides the semantics.)
- **Q4**: REST Namespace index ops rejected with a clear error initially —
OK?
## References
- lance-spark index DDL:
`docs/src/operations/ddl/{create-index,drop-index,show-indexes}.md` in
lance-format/lance-spark
- Lance transaction & CreateIndex compatibility semantics:
`docs/src/format/table/transaction.md` in lance-format/lance
- lance-namespace REST index endpoints: `IndexApi.md` in
lance-format/lance-namespace
- Doris external-catalog mutation precedent: `IcebergMetadataOps` /
`ExternalMetadataOps`; internal index DDL chain: `AlterTableCommand` /
`ShowIndexCommand` / `BuildIndexOp`
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