perf(api): normalize import batches in bounded parallel windows

[DecisionNerd]

Summary

Import validation normalizes every original input batch serially. Run independent batches in byte-admitted windows on the existing private compute pool, then append their ordered results on the coordinator. Preserve original batch boundaries, generated UUID ordinals, replay IDs, within-chunk refusals, durable successful prefixes, cancellation and cache cleanup. One-thread policy remains inline. No append overlap is introduced.

Windows admit at most four batches and a conservative retained-buffer/scratch estimate up to min(memory budget / 4, 256 MiB). One decoded lookahead can coexist; oversized single batches keep baseline behavior. This is admission accounting, not complete allocator accounting.

Three quiet matched Graph500 S18 pairs under equal 16-CPU/4-GiB process-tree limits passed the predeclared gate: validate median 25.777 → 24.674 s (4.28% reduction), with improvement in all pairs; normalization 1.02 → 2.88 effective cores. Complete ingest fell 4.03%, while CPU rose 2.67% and cgroup peak rose about 58 MiB. Cgroup peak includes cache, not RSS. This does not qualify the full ladder or #1387's floor.

Evidence and raw provenance: report, samples.

Validation

• Release API library before the counter correction: 753 passed, two existing ignored. After correction: all 27 import-session tests pass, including the actual closed diagnostic work-counter regression. The unchanged schema/certifier accepts tiny lifecycle and S6/S7/S8 growth certification, including the growth oracle; all six final S18 validate/commit receipts also pass schema validation.
• Private-pool ordering/concurrency test passed; all 26 import-session tests also pass on one CPU after the final fixture portability edit.
• Four fixed-run digests also match across all six full S18 observations. Real serial/parallel import compares four authenticated shaped-run digests and every encoded payload under the established recorded-clock fixture, then commits, reopens and queries. The session-clock defect tracked in fix(storage): shaped output bytes are not reproducible across sessions, because a wall clock is written into the runtime catalog #1416 remains unresolved; the existing nonce-bearing ordinal control exception remains narrow.
• Strict API/exec Clippy, formatting, source-size policy, make pre-push-fast, and make gate-registry-check passed.
• Independent review verified ordering, recovery, cleanup and receipt-based equivalence. CodeRabbit reviewed the production candidate. Its test-hang concern is addressed by a bounded rendezvous retaining the overlap assertion; serial mutation fails in 10 seconds and restored code passes. Independent review verified the correction. Initial CI identified unsupported work counter names; the correction emits supported rows without changing the closed schema, and the final current-main performance series supersedes the original measurements.

Closes #1472

[coderabbitai]

Walkthrough

The import pipeline moves batch normalization into a dedicated module. It adds ordered compute-pool mapping, byte-budgeted batching, cancellation checks, and decode-error draining. Validation and recovery tests cover ordering, durable prefixes, determinism, and final graph state.

Changes

Import normalization pipeline

Layer / File(s)	Summary
Ordered compute-pool mapping crates/graphforge-exec/src/compute_pool.rs	ComputePool::map_ordered runs operations inline for one thread and on the private Rayon pool otherwise. Both paths preserve input order.
Byte-budgeted normalization window crates/graphforge-api/src/import_session/normalization.rs, crates/graphforge-api/src/import_session/normalization/tests.rs	The new normalization module estimates batch weight, limits pending work by bytes and workers, preserves ordered results, records normalization work, and handles cancellation. Tests cover ordering, duplicates, errors, byte admission, and cancellation.
Validation and decode-drain integration crates/graphforge-api/src/import_session.rs, crates/graphforge-api/src/import_session/normalization/tests.rs	Validation delegates normalization to normalization::for_each. Arrow and Parquet decoding drain admitted batches through None before returning decode errors. Recovery and end-to-end tests verify durable prefixes and serial/parallel determinism.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~60 minutes

Change: Refactor

Sequence Diagram(s)

sequenceDiagram
  participant SourceReader
  participant normalization_for_each
  participant ComputePool
  participant ValidationConsumer
  SourceReader->>normalization_for_each: decode source batches
  normalization_for_each->>ComputePool: submit admitted batches
  ComputePool-->>normalization_for_each: return ordered normalized batches
  normalization_for_each->>ValidationConsumer: consume normalized batch
  SourceReader-->>normalization_for_each: signal None after decode failure
  normalization_for_each->>ValidationConsumer: drain admitted batches

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Merge Risk: 🔵 Low · up to 43d00

The implementation risk is bounded, but the new test can stall CI indefinitely. Remove the blocking rendezvous before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 53.57% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 28 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR addresses all coding objectives in #1472. It parallelizes independent batch normalization with bounded byte-based windows on the private compute pool and preserves inline execution for one-thre…
Out of Scope Changes check	✅ Passed	The changes stay within #1472. The import-session refactor supports batch decoding, normalization, draining, and durable-prefix behavior. The compute-pool method enables the required bounded parallel …
Title check	✅ Passed	The title clearly describes the primary change: bounded parallel normalization of import batches in the API.
Description check	✅ Passed	The description provides a clear summary, implementation constraints, performance results, validation evidence, testing details, linked issue, and known limitations. It omits several template checklis…

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[DecisionNerd]

@coderabbitai review

Please review final integration head ed3a843, focused on original-batch/replay order, earliest-error and durable-prefix preservation, cancellation/joined private-pool work, and byte admission. Local API tests (753 passed), forced single-CPU import tests (26 passed), strict Clippy, fast checks, and independently reviewed quiet S18 measurements pass. The previous queue candidate has merged, so this diff is now stable against current main. Exact-head CI is running.

The docs are excluded by repository review filters. Independent evidence review verified all six raw successful/quiet observations and hashes: median validate 25.663 → 24.351 s, every pair improved, normalization 0.99 → 2.84 effective cores. CPU rose 2.67%, cgroup memory rose about 66 MiB; the report distinguishes estimated admission, one decoded lookahead, and cgroup cache-inclusive peak. Four fixed-run digests match across all six full S18 runs; a separate fixed-recorded-clock fixture compares actual encoded payload bytes and reopens the published graph. No claim is made to fix #1416.

[coderabbitai]

@DecisionNerd: I will review pull request #1497 with focus on the specified concurrency, ordering, recovery, cancellation, and byte-admission behavior.

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[DecisionNerd]

@coderabbitai review

Please review final head 43d00f43c2309e321bcad330ac3762497112963b. Focus on original batch ordering/replay identifiers, within-chunk refusals, durable prefix preservation across decoder or normalization errors, cancellation and joining, byte admission bounds, and the closed diagnostic work-counter correction. The final candidate passes actual tiny and S6/S7/S8 growth lifecycle certification and all six S18 receipt schema checks. Final evidence has been independently checked; the original timing series is retained separately with its diagnostic contract defect explained.

[coderabbitai]

@DecisionNerd: I will review pull request #1497 at commit 43d00f43c2309e321bcad330ac3762497112963b. I will focus on the specified ordering, recovery, cancellation, admission-bound, and diagnostic-counter behavior.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
In `@crates/graphforge-exec/src/compute_pool.rs`:
- Around line 140-151: Remove the std::sync::Barrier creation and barrier.wait
call from the map_ordered test closure. Preserve the existing
graphforge-compute- thread-name assertion and value transformation without
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Reviewing files that changed from the base of the PR and between 43413cf and 43d00f4.

⛔ Files ignored due to path filters (2)

• docs/development/evidence/parallel-normalization-1472.json is excluded by !**/docs/**
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📒 Files selected for processing (4)

• crates/graphforge-api/src/import_session.rs
• crates/graphforge-api/src/import_session/normalization.rs
• crates/graphforge-api/src/import_session/normalization/tests.rs
• crates/graphforge-exec/src/compute_pool.rs

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