perf(ddx-ad): keep the SQL surface's programs between calls by alxmrs · Pull Request #164 · xqlsystems/ddx

alxmrs · 2026-10-19T02:14:15Z

Closes #84.

What changed. ddx_ad::rewrite is what ad::sql / sql_all (Rust) and ddxdb.ad.sql / Context.sql (Python) call. Until now it re-planned every program on the engine on every call (SQL → optimized plan → Substrait) and rebuilt it with ddx_ad::grad / vjp / jvp. So a training loop paid for differentiating its loss on every step. In the GPT demo of xarray-sql's ML benchmarks that was about 1.5 s of a 2.4 s step, of which DataFusion's optimizer alone is 800 ms. The program itself depends only on the tables' names and schemas and the views' definitions, not on their values.

rewrite now takes a Programs. A program kept there from an earlier call is run again instead of built. A program is kept under:

its transform and wrt columns;
its query text and its row restrictions (the WHERE layer = 1 pushdown);
a new optional Backend::plan_key of each query.

plan_key is text that changes whenever the engine's plan could. On DataFusion it is the plan before optimization, printed with its schemas (display_indent_schema). DataFusion expands every view, transitively, while it turns SQL into a plan, so this text holds each view's current definition and each table's columns, types and nullability. ddx never resolves a table or view name itself. On the nn model it costs about 2 ms. A backend without plan_key (the default) keeps nothing.

Rust. ad::sql / sql_all keep their signatures. The Programs lives on the SessionContext as a config extension, so it goes away with the context and is shared by its clones.
Python. ddxdb.Programs is new, and ddxdb.rewrite(…, programs=…) takes one. ddxdb.ad keeps one per SessionContext in a WeakKeyDictionary. DataFusionBackend gains plan_key, and the Backend protocol documents it as optional.
Size. At most 16 programs are kept, the least recently used dropped first. A miss costs only a rebuild, i.e. the old behaviour. The size is fixed for now, as discussed on the issue.

What could have gone wrong, and how the tests cover it. New file crates/ddx-datafusion/tests/sql_programs.rs. Which program ran shows in the table names the rewritten statement reads: each program writes under a prefix of its own, __ddx_{id}_. The tests:

A stale program on new values. Replacing w's values with the same schema runs the same program, and the gradient is of the new values.
A stale program on a new schema. val DOUBLE NOT NULL becomes nullable. The issue's case: a kept program would fail to bind, because it states each column's nullability. The program is rebuilt instead.
A redefined view. CREATE OR REPLACE VIEW with the same schema but a different definition rebuilds, and the gradient changes from 8·val to 18·val.
Nested calls. A Hessian-vector product (jvp over a grad column) is kept with the inner program. The outer program reads the inner one's tables by name, so the outer's text changes whenever the inner one is rebuilt.
Restrictions. WHERE i = 1 and WHERE i = 2, alternated, each keep their own program, and each gives the right rows.
Overlapping calls. A program's runs write the same tables, so rewrite takes a program out of the cache while it runs. Four spawned calls on a multi-threaded runtime all get the right gradient.
The window before release. The first version put a program back as rewrite returned, while the caller still had to plan the statements that read its tables. A call made in that window would have run the program again, overwriting those tables, then dropped them when it released its own. Now Rewritten carries the programs, and Rewritten::release keeps them only after dropping the tables; ddxdb's Rewritten.release goes through the same Rust. a_program_is_kept_again_only_once_its_tables_are_released (Rust and Python) makes a call in that window and fails on the old order. (Found by CodeRabbit.)
Negative control. I ran a mutant whose plan_key is the SQL text alone. It fails exactly the schema test (with the binding error) and the view test.
Cache unit tests (crates/ddx-ad/src/sql/cache.rs): a program can be taken only once, keeping under an existing key replaces it, and the least recently used program goes first.
Python (test_ad.py): a second ad.sql reuses the program on new values; a new schema rebuilds; rewrite keeps programs only for a backend that has plan_key.

One semantic change. DataFusion's optimizer folds now() into a literal. So a kept program whose query reads now() keeps the time of the call that built it. This is documented on ad::sql, sql_all and Programs. Volatile functions such as random() are not folded, so they are unaffected.

Measured (release build, i7-8700, median step of nn.rs's model):

	before	after
SQL training step	107 ms	91 ms
program built once	88 ms	88 ms

So the SQL path is within 3% of the program path, which meets the issue's "within about 10%". training_with_sql_grad_learns runs 25 steps again, as the issue asked; it had been trimmed to 15 because of this cost. The GPT replay from #158 should drop by about the 1.5 s of rebuild. I haven't rerun it yet.

Docs. Design §4.8 (the SQL calls) mentions the cache. Decision S11 (each program's tables live under their own prefix) now notes that ad::sql keeps programs and takes one out while it runs. New decision S20 records the key and the rejected alternatives:

keying on the optimized plan, which wouldn't skip the optimizer;
keying on the statement plus schemas ddx looks up itself;
an explicit prepared statement, which every caller would have to adopt.

ddxdb's README shows programs= for other engines.

Breaking. ddx_ad::rewrite takes &Programs as its second argument, and Rewritten::release consumes the Rewritten and takes the same &Programs. Rewritten no longer derives Clone or PartialEq, since it now holds the programs. Note for #152: its decisions now need to become S21–S23, since this PR takes S20.

cargo clippy --workspace --all-targets -- -D warnings is clean. Locally, these pass: ddx-ad's unit tests, sql_programs, nn, sql_grad, sql_vjp, sql_jvp, sql_nesting, sql_adversarial, and ddxdb's 51 Python tests. I'm leaving the rest to CI.

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Summary by CodeRabbit

New Features
- SQL rewrite programs can be reused across calls, with results reflecting current table values. Programs are rebuilt when relevant table schemas or view definitions change.
- Python and Rust APIs now provide a reusable program cache. Backends without plan-key support continue to build programs for each rewrite.
- Rewritten tables are released before their programs become available for reuse.
Documentation
- Updated guidance covers program reuse, cache behavior, and the now() value retained by cached queries.

ddx_ad::rewrite planned and built every program on every call, so a training loop paid for differentiating its loss each step. It now keeps each program in a Programs the caller passes, under the program's transform, wrt, query and restrictions and a new optional Backend::plan_key of each query: on DataFusion, the plan before optimization printed with its schemas, which holds every view's definition and every table's types and nullability. A hit skips both the engine's optimizer and the build. ddx-datafusion keeps one Programs per SessionContext, ddxdb.ad one per context in a weak map. Closes #84. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CvszJhH8pn8H9G69wEPMU2

coderabbitai · 2026-10-19T02:14:31Z

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Reviewing files that changed from the base of the PR and between 72c3be3 and 0c34dc5.

📒 Files selected for processing: 8

crates/ddx-ad/src/sql/cache.rs
crates/ddx-ad/src/sql/mod.rs
crates/ddx-datafusion/src/ad.rs
crates/ddx-datafusion/tests/sql_programs.rs
docs/design.md
python/ddxdb/ddxdb/__init__.py
python/ddxdb/src/lib.rs
python/ddxdb/tests/test_ad.py

🚧 Files skipped from review as they are similar to previous changes: 8

crates/ddx-datafusion/src/ad.rs
python/ddxdb/tests/test_ad.py
crates/ddx-ad/src/sql/cache.rs
python/ddxdb/src/lib.rs
docs/design.md
crates/ddx-datafusion/tests/sql_programs.rs
crates/ddx-ad/src/sql/mod.rs
python/ddxdb/ddxdb/init.py

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📝 Walkthrough

The SQL rewrite path now reuses built derivative programs through a bounded cache. Backend plan keys determine when programs can be reused. DataFusion and Python integrations retain caches across calls and include tests for reuse, rebuilding, and release behavior.

Changes: SQL program cache and rewrite

Layer / File(s)	Summary
Cache identity and storage `crates/ddx-ad/src/run.rs`, `crates/ddx-ad/src/sql/cache.rs`, `crates/ddx-ad/src/sql/plan.rs`, `crates/ddx-ad/src/lib.rs`	`Backend` adds an optional `plan_key`. `Programs` stores up to 16 programs and evicts the least-recently-used entry. Planner jobs expose derivative identity and support adopting cached programs.
Rewrite cache adoption and return `crates/ddx-ad/src/sql/mod.rs`, `docs/design.md`	`rewrite` accepts a `Programs` registry, adopts matching programs, and returns programs to the cache after table cleanup, including after execution failure. Program construction retains its restriction-pushdown fallback.
DataFusion context cache and validation `crates/ddx-datafusion/src/ad.rs`, `crates/ddx-datafusion/src/engine.rs`, `crates/ddx-datafusion/tests/ad_simulation/sql.rs`, `crates/ddx-datafusion/tests/nn.rs`, `crates/ddx-datafusion/tests/sql_programs.rs`	DataFusion uses schema-bearing logical plans for plan keys and retains a registry per context. Tests cover reuse, updated table values, schema and view changes, restrictions, dependent programs, and overlapping calls. The training test runs 25 iterations.
Python cache API and context reuse `python/ddxdb/ddxdb/__init__.py`, `python/ddxdb/ddxdb/ad.py`, `python/ddxdb/src/lib.rs`, `python/ddxdb/tests/test_ad.py`, `python/ddxdb/README.md`	Python exposes `Programs` and an optional backend `plan_key`. `rewrite` accepts an optional registry, and DataFusion SQL calls retain registries per context. Tests cover reuse, schema changes, backends without plan keys, and unreleased rewrites.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant sql_all
  participant SessionContext
  participant ddx_ad_rewrite
  participant DataFusion_plan_key
  participant Programs
  participant Backend_plan_sql
  Caller->>sql_all: execute SQL statements
  sql_all->>SessionContext: get or install Programs registry
  sql_all->>ddx_ad_rewrite: rewrite with registry
  ddx_ad_rewrite->>DataFusion_plan_key: derive key for SQL plan
  DataFusion_plan_key-->>ddx_ad_rewrite: return schema-bearing plan key
  ddx_ad_rewrite->>Programs: take matching built program
  alt cache hit
    Programs-->>ddx_ad_rewrite: return cached program
  else cache miss
    ddx_ad_rewrite->>Backend_plan_sql: plan and build derivative program
    Backend_plan_sql-->>ddx_ad_rewrite: return built program
  end
  ddx_ad_rewrite->>Programs: keep program after execution and release

Merge Risk: ⚪ Minimal · up to 0c34d

No merge-blocking issue was established; the change is ready for normal checks.

Security architecture risk: 🟡 Moderate · up to 72c3b

The reuse lifecycle releases ownership too early, allowing overlapping calls to overwrite or remove results that an earlier call still needs. No privilege escalation or cross-tenant access has been established.

Retained concerns

Medium · reliability · inferred: A cached program becomes reusable before its result-table ownership ends. rewrite returns programs to Programs before returning Rewritten, although callers still need its named tables until planning or execution and release finish. A second matching rewrite can therefore replace those tables; either result's name-based cleanup can then delete tables needed by the other call. Rust sql_all also has an asynchronous planning window after cache return. This newly introduced lifecycle gap breaks cross-call result ownership and failure containment within a shared backend catalog; it is not evidence of a cross-tenant authorization bypass.

Security review details

Security Blast Radius

inferred — The established ownership risk is bounded to matching rewrites sharing a registry and backend table namespace. Automatic integrations scope registries to contexts; explicit callers control registry sharing. The inspected evidence does not establish cross-tenant reachability or gained privileges.

Security Findings and Attack Paths

inferred — A caller can retain an unconsumed Rewritten result and perform a second matching rewrite using the same registry. The second call can replace the first result's named tables, and releasing either result can remove the other's tables. Concurrent Rust SQL calls expose a related scheduling window between program restoration and result binding. This supports an integrity and availability concern, not a verified authorization bypass.

Trust Boundaries and Controls

observed — The backend remains responsible for planning, table lookup, materialization, and deletion. Each program run binds checks and steps against backend schemas and executes its checks before materializing steps; caching does not remove that execution-time control.

Resilience and Maintainability Implications

observed — Cancellation can skip asynchronous cleanup and leave materialized tables. This behavior was already documented at the PR base and is not retained as a newly introduced concern. Cancellation also skips cache restoration, dropping the taken executable rather than making it concurrently reusable.

Hardening Proposals

proposed — Extend the program namespace lease through result binding and cleanup, or separate reusable executable identity from per-invocation table identity with ownership-aware release. Validate the transition with a deterministic interleaving that pauses the first call before result binding while a second matching call attempts reuse.

Pre-merge checks: 3 · 2

Failed checks: 2 warnings

Check name	Status	Explanation	Resolution
Linked Issues check		The implementation meets the three `#84` done criteria. It reuses programs after value changes, rebuilds after a schema change, and restores the 25-step SQL training test. The current Rust `Programs` AP…	Add a public `Programs::clear()` operation and the equivalent Python API. Add tests that populate the cache, clear it, and verify that the next rewrite rebuilds the program.
Docstring Coverage		Docstring coverage is 65.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 69 functions across 14 files. (1 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: retaining SQL programs between calls for performance.
Out of Scope Changes check		The changes remain within `#84`. The cache, plan-key invalidation, LRU behavior, release ordering, context ownership, documentation, and Rust/Python tests support SQL program reuse and safe rebuilding. …
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.

Full details: Out of Scope Changes check

Explanation

The changes remain within #84. The cache, plan-key invalidation, LRU behavior, release ordering, context ownership, documentation, and Rust/Python tests support SQL program reuse and safe rebuilding. No unrelated change is demonstrated.

Full details: Linked Issues check

Explanation

The implementation meets the three #84 done criteria. It reuses programs after value changes, rebuilds after a schema change, and restores the 25-step SQL training test. The current Rust Programs API exposes new, but no public clear; the Python Programs API also exposes no clear operation. This leaves the explicit cache invalidation requirement in #84 incomplete.

Resolution

Add a public Programs::clear() operation and the equivalent Python API. Add tests that populate the cache, clear it, and verify that the next rewrite rebuilds the program.

Full details: Docstring Coverage

Explanation

Docstring coverage is 65.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 69 functions across 14 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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Inline comments:
Review comments at @crates/ddx-ad/src/sql/mod.rs:
- Around line 183-187: Update the rewrite flow so it does not return cached
programs through programs.keep before the caller releases their tables. Carry
each cache key and program in Rewritten, then restore them from
Rewritten::release after releasing the tables, ensuring concurrent sql_all calls
cannot reuse the program prematurely.

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📒 Files selected for processing: 16

crates/ddx-ad/src/lib.rs
crates/ddx-ad/src/run.rs
crates/ddx-ad/src/sql/cache.rs
crates/ddx-ad/src/sql/mod.rs
crates/ddx-ad/src/sql/plan.rs
crates/ddx-datafusion/src/ad.rs
crates/ddx-datafusion/src/engine.rs
crates/ddx-datafusion/tests/ad_simulation/sql.rs
crates/ddx-datafusion/tests/nn.rs
crates/ddx-datafusion/tests/sql_programs.rs
docs/design.md
python/ddxdb/README.md
python/ddxdb/ddxdb/__init__.py
python/ddxdb/ddxdb/ad.py
python/ddxdb/src/lib.rs
python/ddxdb/tests/test_ad.py

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rewrite put each program back in Programs as it returned, while its caller had yet to plan the statements that read the program's tables. A call in between could run the program again, rewriting those tables, and drop them on its release. Rewritten now carries the programs, and Rewritten::release keeps them after dropping the tables; ddxdb's Rewritten.release goes through it. A test makes a call in that window and fails on the old order. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CvszJhH8pn8H9G69wEPMU2

alxmrs

LGTM

ddxdb 0.3.3 keeps each gradient program between calls (xqlsystems/ddx#164), plans each CTE an objective reads twice on its own (xqlsystems/ddx#168), and differentiates attention's masked product as jax.grad does (xqlsystems/ddx#162). Alternating runs with 0.3.2 on DataFusion: - GPT training step, SGD: 2.8 s -> 1.2 s (first step 2.0 s) - GPT training step, AdamW: 3.2 s -> 1.55 s - attention gradient at 512 tokens: 2.8 s -> 1.1 s (window), 2.7 s -> 1.3 s (GROUP BY) Every check against JAX still passes. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01NyN7idACeDMh94qrnFMu6h

coderabbitai Bot reviewed Oct 19, 2026

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Comment thread crates/ddx-ad/src/sql/mod.rs Resolved

alxmrs commented Oct 19, 2026

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alxmrs merged commit eeedf48 into main Oct 19, 2026
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alxmrs deleted the perf/84-program-cache branch October 19, 2026 15:00

alxmrs mentioned this pull request Oct 19, 2026

docs: plan DuckDB-Python as Substrait in, SQL out; refresh the design #152

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github-actions Bot mentioned this pull request Oct 19, 2026

chore: release v0.2.3 #163

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This was referenced Oct 19, 2026

perf(ddx-ad): plan each CTE an objective reads more than once on its own #168

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perf(ddx-ad): push readers' filters and columns into shared CTEs #170

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test(ddx-datafusion): fuzz the SQL surface's fast paths #173

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alxmrs mentioned this pull request Oct 29, 2026

plan_sql: DataFusion optimizes the whole CTE-inlined objective before ddx differentiates it #156

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perf(ddx-ad): keep the SQL surface's programs between calls - #164

perf(ddx-ad): keep the SQL surface's programs between calls#164
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