id: ADR-0017 title: Adopt D14: memoize on declared inputs, the pass version and the engine profile status: superseded date: 2026-09-13 deciders: [paul-heyse] level: decision principles: [DM-31, DM-32, DM-33, DM-28] blueprint: [§D14, §14.3, §14.4] review: docs/design_review/reviews/design_review_arrow-native-idaes-core-blueprint-rev2_2026-09-13.md#7-principle-findings evidence: Interface-checked supersedes: [] superseded-by: ADR-0041 revisit: A measurement shows sub-pass granularity finer than per-instance is needed (the same trigger as ADR-0020), or an undeclared read is found in a pass verification: tests/engine memo-key tests; the two-process byte-equality test for the plan fingerprint (ADR-0019)

ADR-0017: Adopt D14: memoize on declared inputs, the pass version and the engine profile

Context

Blueprint D14 keys memoization on the content hashes of a pass’s declared inputs, the pass version and — for plan-executing passes — the engine profile. The first review’s F13 asked whether salsa should own this, and the second review’s R2-1 found the plan fingerprint not reproducible as specified.

Scope

Binds the memo key’s shape and the invalidation granularity. Whether salsa is adopted is ADR-0020; what the fingerprint is for is ADR-0019.

Drivers

An undeclared read is a contract violation, not something to track; a value change must not invalidate structure; an engine upgrade must invalidate exactly the plan-executing passes.

Options

Track dependencies automatically with salsa — deferred by ADR-0020: it duplicates the declared inputs. Key on file mtimes — rejected: not semantic (DM-32).

Outcome

The memo key is (pass_id, pass_version, content hashes of cache_key_inputs, engine profile hash for plan-executing passes). Backdating is inherent: byte-identical outputs leave the next pass’s key unchanged.

Consequences

Every pass must declare its inputs exhaustively, and pass_specs.cache_key_inputs becomes part of the reviewed surface of a pass.

Compensating controls

The §14.4 invalidation table is explicit per change kind; the canonical graph never depends on a parameter value, so a parameter change invalidates exactly the case-bound rows.

Confirmation

tests/engine asserts that a re-run on changed inputs producing identical bytes does not invalidate downstream passes.

Pros and cons

Declared inputs are work; automatic tracking is a second dependency system beside pass_specs.

More information

Blueprint §D14, §14.3 (pass engine), §14.4 (incrementality); review findings F13 and R2-1.

Status history

• 2026-09-13 — accepted with the repository-seeding pull request (backfilled from blueprint revision 3).
• 2026-09-13 — superseded by ADR-0041.