docs(design): defer RJN-3 (fanout) and RJN-4 (bench) as N/A after RJN-2 rename#4676
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…-2 rename RJN-2 (PR #4660, merged) chose the rename path over the fanout-refactor path, discharging the RJN-1 audit (PR #4656, merged) with apply_chunk_parallel -> apply_one_chunk plus a rustdoc redirect to apply_batch_parallel. RJN-3 (implement fanout) and RJN-4 (bench scheduler shape) were the "if RJN-2 chose refactor" branch that did not get taken; this doc closes both. - RJN-3 stays closed: zero production callers of apply_one_chunk; the real multi-chunk win sits in apply_batch_parallel, where ABW-1 (PR #4670) already recommended deferring per its quantified 1.03x-1.50x speedup range; the ABW-2/3/4 closure doc defers that track pending BR-3j.f (#2508) bench data. - RJN-4 is N/A: with RJN-3 deferred there is no "after" cell to measure; the production-weighted scheduler-shape bench effort belongs in parallel_receive_delta_perf via BR-3j.f, not at the per-chunk entry point. - Re-open conditions: a production caller of apply_one_chunk ships AND profiling shows the per-chunk path is hot. Project memory references project_rayon_join_per_chunk_noop.md and project_apply_batch_write_serial.md - both observations remain accurate under the renamed function.
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This was referenced May 21, 2026
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Summary
docs/design/rjn-3-4-fanout-deferred-2026-05-21.md, a closure note for the RJN-3 (implement fanout) and RJN-4 (bench scheduler shape) tracks following the RJN-2 rename outcome.apply_chunk_parallel->apply_one_chunk) over the fanout refactor, discharging the RJN-1 audit (PR docs(audits): apply_chunk_parallel call sites and per-chunk dispatch benefit (RJN-1) #4656, merged). RJN-3/4 were the "if RJN-2 chose refactor" branch that was not taken; this doc closes both as deferred N/A.docs/design/abw-2-pipelined-verify-write-deferred-2026-05-21.md(predecessor PR docs(audit): apply_batch_parallel verify-vs-write overlap potential (ABW-1) #4670 merged) - the real multi-chunk parallelism win lives inapply_batch_parallel, where ABW-1 already recommended deferring pending BR-3j.f (feat(daemon): add max verbosity parsing and enforcement #2508) bench evidence. Pursuing RJN-3 in parallel would split the refactor budget across two entry points the dispatcher does not reach today.apply_one_chunkmust ship AND profiling must show the per-chunk path is hot.References
docs/audits/rjn-1-apply-chunk-parallel-call-sites-2026-05-21.mddocs/audits/abw-1-apply-batch-verify-write-overlap-2026-05-21.mddocs/design/abw-2-pipelined-verify-write-deferred-2026-05-21.mdproject_rayon_join_per_chunk_noop.md,project_apply_batch_write_serial.mdapply_batch_parallel: PIP-3+5 (PR perf(transfer): enable parallel receive-delta by default via Path B heuristic (PIP-3 + PIP-5) #4666)Test plan
cargo fmt --allclean.