feat(backend/kernel): route use_sea=True through the Rust kernel via PyO3 by vikrantpuppala · Pull Request #787 · databricks/databricks-sql-python

vikrantpuppala · 2026-05-14T15:11:20Z

Summary

Phase 2 of the PySQL × kernel integration plan (design doc). Wires `use_sea=True` to a new `backend/kernel/` module that delegates to the Rust kernel via the `databricks_sql_kernel` PyO3 extension (kernel PR #13).

This replaces the previous ADBC POC branches (`backend/adbc/` and `backend/adbc_dm/` on `adbc-rust-backend-via-dm`, which were never merged) with a clean port that uses the kernel's v0 Databricks-native API directly instead of layering through ADBC.

What `use_sea=True` now does

import databricks.sql

# PAT auth — works end-to-end today
with databricks.sql.connect(
    server_hostname=...,
    http_path=...,
    access_token="dapi...",
    use_sea=True,
) as conn:
    with conn.cursor() as cur:
        cur.execute("SELECT * FROM main.default.t LIMIT 100")
        rows = cur.fetchall()  # rows come from the kernel via PyO3

`use_sea=False` (Thrift) is unchanged. The native `backend/sea/` pure-Python SEA backend is left in place — no users on `use_sea=True` after this PR but the module stays; its long-term fate is out of scope here.

New module layout

File	Purpose
`src/databricks/sql/backend/kernel/client.py`	`KernelDatabricksClient(DatabricksClient)`. Lazy-imports `databricks_sql_kernel` so a connector install without the kernel wheel doesn't fail at startup — only `use_sea=True` surfaces the missing-extra ImportError.
`src/databricks/sql/backend/kernel/auth_bridge.py`	Translates the connector's `AuthProvider` to kernel `Session` auth kwargs. PAT (including `TokenFederationProvider`-wrapped PAT — every provider is wrapped, so the naive `isinstance(AccessTokenAuthProvider)` check has to look through the wrapper) routes through `auth_type='pat'`. Everything else routes through `auth_type='external'` with a callback that delegates to `auth_provider.add_headers({})`.
`src/databricks/sql/backend/kernel/result_set.py`	`KernelResultSet(ResultSet)`. Duck-typed over the kernel's `ExecutedStatement` (sync exec) and `ResultStream` (metadata + async await_result), since both expose `arrow_schema / fetch_next_batch / fetch_all_arrow / close`. FIFO batch buffer for `fetchmany(n)` semantics.
`src/databricks/sql/backend/kernel/type_mapping.py`	Arrow → PEP 249 description-string mapper.

Error mapping

`KernelError.code` → PEP 249 exception class, in a single table in `client.py`. Structured fields (`sql_state`, `error_code`, `query_id`, `http_status`, `retryable`, `vendor_code`) are copied onto the re-raised exception so callers can branch on `err.code` / `err.sql_state` directly. Live e2e verified: bad SQL on `use_sea=True` surfaces as `DatabaseError(code='SqlError', sql_state='42P01')`.

Packaging

`pip install 'databricks-sql-connector[kernel]'` pulls in the kernel wheel. Without it, `use_sea=True` raises:

```
ImportError: use_sea=True requires the databricks-sql-kernel package.
Install it with: pip install 'databricks-sql-connector[kernel]'
```

Local dev (today): `cd databricks-sql-kernel/pyo3 && maturin develop --release` into the connector's venv.

⚠️ Known gaps — acknowledged follow-ups

Gap	Surface	Why deferred
Parameter binding	`execute_command(parameters=[...])` raises `NotSupportedError`	PyO3 `Statement.bind_param` lands in a small follow-up PR on the kernel repo
Statement-level `query_tags`	Raises `NotSupportedError`	Same follow-up — PyO3 needs to expose `statement_conf`
`get_tables(table_types=[...])` filter	Returns unfiltered rows	Native SEA's filter is keyed on `SeaResultSet`; small port needed
External-auth end-to-end	OAuth surfaces `ProgrammingError` from the kernel's "reserved" guard	Kernel-side enablement PR covers this — once it lands, OAuth/MSAL/federation start working through this backend automatically
Volume PUT/GET (staging)	Not supported	Kernel has no Volume API yet

Test plan

Unit tests — 37 new tests across:
- `tests/unit/test_kernel_auth_bridge.py` — PAT, federation-wrapped PAT, OAuth → External trampoline (with call-counter check that the callback fires per request, not cached), error paths (silent provider, non-Bearer header)
- `tests/unit/test_kernel_type_mapping.py` — Arrow type mapping per type, description-tuple shape, fallback to `str()` for unknowns
- `tests/unit/test_kernel_result_set.py` — buffer semantics, `fetchmany` slicing within batch + across batch boundaries, idempotent close, close() swallowing handle-close failures, empty stream
Full pre-existing unit suite — 600 pass; one pre-existing failure (`test_useragent_header` — agent detection adds `agent/claude-code` in this env, fails on `main` too) is unrelated to this change.
Live e2e against dogfood with `use_sea=True` (PAT): SELECT 1, `SELECT * FROM range(10000)`, `fetchmany` pacing, `fetchall_arrow`, all four metadata calls (75 catalogs / 144 schemas in `main` / 47 tables in `system.information_schema` / 15 columns), `session_configuration={'ANSI_MODE': 'false'}` round-trips, bad SQL surfaces as DatabaseError with `code='SqlError'` and `sql_state='42P01'`. All checks pass.

This pull request and its description were written by Isaac.

Phase 2 of the PySQL × kernel integration plan (databricks-sql-kernel/docs/designs/pysql-kernel-integration.md). Wires `use_sea=True` to a new `backend/kernel/` module that delegates to the Rust kernel via the `databricks_sql_kernel` PyO3 extension (kernel PR #13). New module: `src/databricks/sql/backend/kernel/` - `client.py` — `KernelDatabricksClient(DatabricksClient)`. Lazy- imports `databricks_sql_kernel` so a connector install without the kernel wheel doesn't `ImportError` at startup; only `use_sea=True` surfaces the missing-extra message. Implements open/close_session, sync + async execute_command (async_op=True goes through `Statement.submit()` and stashes the handle in a dict keyed on `CommandId`), cancel/close_command, get_query_state, get_execution_result, and the metadata calls (catalogs / schemas / tables / columns) via `Session.metadata().list_*`. Real server-issued session and statement IDs flow through (no synthetic UUIDs). - `auth_bridge.py` — translate the connector's `AuthProvider` into kernel `Session` kwargs. PAT (including federation-wrapped PAT — `get_python_sql_connector_auth_provider` always wraps the base in `TokenFederationProvider`, so a naive isinstance check never matches) routes through `auth_type="pat"`. Everything else routes through `auth_type="external"` with a callback that delegates to `auth_provider.add_headers({})`. (External today is rejected by the kernel at `build_auth_provider`; the separate kernel-side enablement PR will flip it on.) - `result_set.py` — `KernelResultSet(ResultSet)`. Duck-typed over `databricks_sql_kernel.ExecutedStatement` (sync execute) and `ResultStream` (metadata + async await_result) since both expose `arrow_schema()` / `fetch_next_batch()` / `fetch_all_arrow()` / `close()`. Same FIFO batch buffer the prior ADBC POC used, so `fetchmany(n)` for n smaller than the kernel's natural batch size doesn't re-fetch. - `type_mapping.py` — Arrow → PEP 249 description-string mapper. Lifted from the prior ADBC POC; centralised here so future kernel-result wrappers reuse the same mapping. Kernel errors → PEP 249 exceptions: `KernelError.code` is mapped in a single table to `ProgrammingError` / `OperationalError` / `DatabaseError`. The structured fields (`sql_state`, `error_code`, `query_id`, …) are copied onto the re-raised exception so callers can branch on them without reaching through `__cause__`. Routing: `Session._create_backend` flips the `use_sea=True` branch to instantiate `KernelDatabricksClient` instead of the native `SeaDatabricksClient`. The native `backend/sea/` module is left in place (no users on `use_sea=True` after this PR; its long- term fate is out of scope here). Packaging: `[tool.poetry.extras] kernel = ["databricks-sql-kernel"]`. `pip install 'databricks-sql-connector[kernel]'` pulls in the kernel wheel; `use_sea=True` without the extra raises a pointed ImportError telling the user how to install it. Known gaps (acknowledged, will be follow-ups): - Parameter binding (`execute_command(parameters=[...])`) raises NotSupportedError — PyO3 `Statement.bind_param` lands in a follow-up. - Statement-level `query_tags` raises NotSupportedError. - `get_tables(table_types=[...])` returns unfiltered rows (the native SEA backend's filter is keyed on `SeaResultSet`; needs a small port to operate on `KernelResultSet`). - External-auth end-to-end blocked on the kernel-side `AuthConfig::External` enablement PR. - Volume PUT/GET (staging operations): kernel has no Volume API. Test plan: - Unit: 37 new tests across `tests/unit/test_kernel_auth_bridge.py` (auth provider → kwargs mapping, including federation-wrapped PAT and the External trampoline call-counter check), `tests/unit/test_kernel_type_mapping.py` (Arrow type mapping + description shape), and `tests/unit/test_kernel_result_set.py` (buffer semantics, fetchmany across batch boundaries, idempotent close, close() swallowing handle-close failures). All pass. - Full unit suite: 600 pre-existing tests still pass; one pre-existing failure (`test_useragent_header` — agent detection adds `agent/claude-code` in this env) was already failing on main, unrelated to this change. - Live e2e against dogfood with `use_sea=True`: SELECT 1, `range(10000)`, `fetchmany` pacing, `fetchall_arrow`, all four metadata calls (returned 75 catalogs / 144 schemas in main / 47 tables in `system.information_schema` / 15 columns), `session_configuration={'ANSI_MODE': 'false'}` round-trips, bad SQL surfaces as DatabaseError with `code='SqlError'` and `sql_state='42P01'` on the exception. All checks pass. Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

The earlier auth_bridge routed OAuth/MSAL/federation through the kernel's External token-provider trampoline (a Python callable the kernel invoked per HTTP request). Removing that for now. Why: routing OAuth into the kernel inherently requires per-request token resolution to keep refresh working during a long-running session. Two viable mechanisms (kernel-native OAuth, or the External callback); both have costs (duplicate OAuth flows vs GIL-per-request). Punting the decision until there's actual demand on use_sea=True. Today: the bridge accepts PAT (including TokenFederationProvider- wrapped PAT, which is how `get_python_sql_connector_auth_provider` always shapes it). Any non-PAT auth_provider raises a clear NotSupportedError pointing the user at use_sea=False (Thrift). This shrinks the auth_bridge to ~50 lines and means the kernel- side External enablement PR is no longer on the connector's critical path — there's no kernel-side prerequisite for shipping use_sea=True for PAT users. Unit tests updated: - TokenFederationProvider-wrapped PAT still routes to PAT (kept). - Generic OAuth provider raises NotSupportedError (new). - ExternalAuthProvider raises NotSupportedError (new). - Silent non-PAT provider raises NotSupportedError (new) — reject the type itself rather than trying to extract a token we already know we can't use. Live e2e against dogfood with use_sea=True (PAT): all checks still pass (SELECT 1, range(10000), fetchmany pacing, four metadata calls, session_configuration round-trip, structured DatabaseError on bad SQL). Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

Moves the previously-ad-hoc /tmp/connector_smoke.py into the repo as a real pytest module under tests/e2e/ — same convention as the rest of the e2e suite. Uses the existing session-scoped `connection_details` fixture from the top-level conftest so it shares the credential surface with every other live test. 11 tests cover: - connect() with use_sea=True opens a session. - SELECT 1: rows + description shape (column name + dbapi type slug). - SELECT * FROM range(10000): multi-batch drain. - fetchmany() pacing across the buffer boundary. - fetchall_arrow() returns a pyarrow Table. - All four metadata methods (catalogs / schemas / tables / columns). - session_configuration={'ANSI_MODE': 'false'} round-trips. - Bad SQL surfaces as DatabaseError with `code='SqlError'` and `sql_state='42P01'` attached as exception attributes. Module-level skips: - `databricks_sql_kernel` not importable → whole module skipped via pytest.importorskip (the wheel hasn't been installed). - Live creds missing → fixture-level skip with a pointed message. Run: `pytest tests/e2e/test_kernel_backend.py -v`. All 11 pass against dogfood in ~20s. Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

vikrantpuppala · 2026-05-14T15:35:24Z

Two updates since the initial PR:

1. Dropped External auth → PAT-only on the kernel backend (25723627). auth_bridge.py now routes PAT (including TokenFederationProvider-wrapped PAT) through the kernel's PAT path; everything else raises NotSupportedError pointing the user at use_sea=False. The kernel-side PR is no longer on this PR's critical path. Why: routing OAuth into the kernel requires per-request token resolution to keep refresh working — two viable mechanisms (kernel-native OAuth, or the External callback), both with costs. Punting the decision until there's pressure.

2. Live e2e tests moved into the repo (6b308156). The previous ad-hoc /tmp/connector_smoke.py is now tests/e2e/test_kernel_backend.py — a proper pytest module using the existing connection_details fixture. 11 tests cover: connect, SELECT 1, range(10000), fetchmany pacing, fetchall_arrow, all four metadata methods, session_configuration round-trip, structured DatabaseError on bad SQL. All 11 pass against dogfood in ~20s. Module skips cleanly when databricks_sql_kernel isn't installed or creds aren't set.

The auth_bridge unit tests are updated: OAuth providers / ExternalAuthProvider now assert NotSupportedError. 39 unit tests pass.

CI is failing across all jobs at \`poetry lock\` time: Because databricks-sql-connector depends on databricks-sql-kernel (^0.1.0) which doesn't match any versions, version solving failed. The kernel wheel isn't yet published to PyPI — we verified the name is available via the Databricks proxy, but the package itself hasn't been built and uploaded yet. Declaring it as a poetry dep (even an optional one inside an extra) requires the version to be resolvable, and \`poetry lock\` runs as the setup step for every CI job: unit tests, linting, type checks, all of them. Fix: drop the \`databricks-sql-kernel\` dep declaration and the \`[kernel]\` extra from pyproject.toml until the wheel is on PyPI. The lazy import in \`backend/kernel/client.py\` still raises a clear ImportError pointing at \`pip install databricks-sql-kernel\` (or local maturin) when use_sea=True is invoked without the kernel present. When the kernel is published, a small follow-up will add back: databricks-sql-kernel = {version = "^0.1.0", optional = true} [tool.poetry.extras] kernel = ["databricks-sql-kernel"] A pointed comment in pyproject.toml documents the deferred change. Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

Three CI failures after the poetry-lock fix uncovered three real issues: 1. pyarrow is optional in the connector. The default-deps CI test job installs without it; the +PyArrow job installs with. The kernel backend's result_set.py + type_mapping.py import pyarrow eagerly (the kernel always returns pyarrow), and the unit tests import the backend at collection time — which crashes the default-deps job at ModuleNotFoundError. Fix: gate the three kernel unit tests on `pytest.importorskip( "pyarrow")` so they skip on default-deps and run on +PyArrow. Verified locally: 39 pass with pyarrow, 3 skipped without. No change to the backend module itself — nothing imports it until use_sea=True is invoked, and pyarrow is on the kernel wheel's runtime dep list so use_sea=True can't hit this either. 2. mypy: KernelDatabricksClient.open_session returns self._session_id, which mypy types as Optional[SessionId] because the field starts as None. Fix: bind the new id to a local non-Optional variable, assign to the field, return the local. CI's check-types runs cleanly on backend/kernel/ now; pre-existing mypy noise elsewhere isn't mine. 3. black --check: black 22.12.0 (the version CI pins) wants reformatting on result_set.py / type_mapping.py / client.py. Applied. Verified locally with the same black version. All 39 kernel unit tests + 619 pre-existing unit tests pass. Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

The +PyArrow CI matrix installs pyarrow but not the databricks-sql-kernel wheel (the wheel isn't on PyPI yet, and the [kernel] extra is deferred — see commit 31ca581). The previous fix gated unit tests on `pytest.importorskip("pyarrow")` but test_kernel_auth_bridge.py was still pulled into a kernel-wheel ImportError because: src/databricks/sql/backend/kernel/__init__.py -> from databricks.sql.backend.kernel.client import KernelDatabricksClient -> import databricks_sql_kernel # ImportError on +PyArrow CI The eager re-export from `__init__.py` was a convenience that broke every consumer that only needed a submodule (type_mapping, result_set, auth_bridge) — they all triggered the kernel wheel import for no reason. Fix: - Drop the eager re-export from `kernel/__init__.py`. Comment documents why and points callers (= session.py::_create_backend, already this shape) at the direct `from .client import ...`. - Drop the no-longer-needed `pytest.importorskip("pyarrow")` / `importorskip("databricks_sql_kernel")` from test_kernel_auth_bridge.py — auth_bridge.py itself has neither dep, so the test now runs on every CI matrix variant. - test_kernel_result_set.py and test_kernel_type_mapping.py keep the pyarrow importorskip because they themselves use pyarrow. Verified locally across the three matrix shapes: - both pyarrow + kernel installed: 39 pass. - pyarrow only (no kernel wheel — the +PyArrow CI shape): 39 pass. - neither: 9 pass (auth_bridge only), 2 modules skip (the others use pyarrow). Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

…sing The connector's coverage CI job runs the full e2e suite, several of whose test classes parametrize ``extra_params`` over ``{}`` and ``{"use_sea": True}``. With ``use_sea=True`` now routing through the Rust kernel via PyO3, those cases die at ``connect()`` with our pointed ImportError because the ``databricks-sql-kernel`` wheel isn't yet on PyPI — and that CI job (sensibly) doesn't try to build it from a sibling repo. Fix: ``pytest_collection_modifyitems`` hook in the top-level ``conftest.py`` that adds a ``skip`` marker to any parametrize case with ``extra_params={"use_sea": True, ...}`` when ``importlib.util.find_spec("databricks_sql_kernel")`` returns ``None``. Behavior change is CI-only — local dev with the kernel wheel installed (via ``maturin develop`` from the kernel repo) runs those cases as before. Once the kernel wheel is published, the [kernel] extra in pyproject.toml gets enabled (see comment block there) and the default-deps CI matrix will install it; the skip then becomes a no-op. Co-authored-by: Isaac Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

vikrantpuppala · 2026-05-14T16:30:04Z

CI status, final: 33 / 34 checks pass.

The one failing check (test-with-coverage, the e2e + coverage job) reports 7 test failures — but all 7 are pre-existing on main, unrelated to this PR. Verified by reproducing them on an independent recent PR (PR for thrift-result-set-heartbeat, run 25725422361, 2 days ago) and confirming the same 6 TestMstMetadata cases fail there too with identical error messages.

Failure breakdown:

Test	Failure	Root cause
`TestMstMetadata::test_cursor_{columns,schemas,tables,catalogs}_in_mst` (4)	`DatabaseError: GetCatalogs/Schemas/Tables/Columns is not supported within a multi-statement transaction`	Server-side change between Apr 28 (last green main run) and today; affects every PR's e2e job
`TestMstMetadata::test_cursor_{columns,tables}_non_transactional_after_concurrent_*` (2)	Same server-side MST limitation	Same as above
`TestPySQLLargeWideResultSet::test_query_with_large_wide_result_set[True-extra_params0]` (1)	`AttributeError: 'TestPySQLLargeWideResultSet' object has no attribute 'assertEqual'`	Latent bug from #772 ("Optimize CI"). Split `LargeQueriesMixin` test classes off `unittest.TestCase` but `fetch_rows` still calls `test_case.assertEqual`. Triggers only when the fetch completes inside the 5-min budget.

My PR contributions to this job (all working as intended):

53 tests now skip cleanly (vs failing). All the extra_params={"use_sea": True} cases — see the conftest hook in 8958e76e. Once databricks-sql-kernel ships to PyPI and the [kernel] extra is wired, these run as live tests.
927 tests pass.

I don't believe my PR should be responsible for fixing the 7 pre-existing failures — they need their own fixes (server-side investigation for MST metadata; switching fetch_rows to pytest assertions for the large-result test). Happy to file follow-up issues if you want.

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feat(backend/kernel): route use_sea=True through the Rust kernel via PyO3#787

feat(backend/kernel): route use_sea=True through the Rust kernel via PyO3#787
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vikrantpuppala commented May 14, 2026

Summary

What `use_sea=True` now does

New module layout

Error mapping

Packaging

⚠️ Known gaps — acknowledged follow-ups

Test plan

Uh oh!

vikrantpuppala commented May 14, 2026

Uh oh!

vikrantpuppala commented May 14, 2026

Uh oh!

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