From the 2026-05-04 download-optimization audit (F4 in docs/superpowers/specs/2026-05-04-download-optimization-audit.md).
The audit speculated 5–15% wall-clock improvement from streaming fragment writes (bytes_stream() end-to-end) instead of resp.bytes().await into a Vec<u8> per fragment. Round-2 research (docs/superpowers/specs/2026-05-21-f3-f6-download-optimization-design.md) showed the claim was speculative: glibc malloc at ~18ns/alloc means 600 fragment allocations cost ~10µs total — not in the top 10 hot frames for a network-bound HLS download. bytes_stream() would ADD per-chunk Arc-decrement traffic (320 Bytes drops per 5 MiB H2 segment vs 1).
Action
Profile first. If cargo flamegraph on a real 4K HLS download (~600 fragments) shows allocator/syscall in the top 10 hot frames, revisit. Otherwise close as no-op.
References
- Spec non-goal:
docs/superpowers/specs/2026-05-21-f3-f6-download-optimization-design.md (F4 dropped after research)
- Audit:
docs/superpowers/specs/2026-05-04-download-optimization-audit.md (F4 section)
From the 2026-05-04 download-optimization audit (F4 in
docs/superpowers/specs/2026-05-04-download-optimization-audit.md).The audit speculated 5–15% wall-clock improvement from streaming fragment writes (
bytes_stream()end-to-end) instead ofresp.bytes().awaitinto aVec<u8>per fragment. Round-2 research (docs/superpowers/specs/2026-05-21-f3-f6-download-optimization-design.md) showed the claim was speculative: glibc malloc at ~18ns/alloc means 600 fragment allocations cost ~10µs total — not in the top 10 hot frames for a network-bound HLS download.bytes_stream()would ADD per-chunk Arc-decrement traffic (320Bytesdrops per 5 MiB H2 segment vs 1).Action
Profile first. If
cargo flamegraphon a real 4K HLS download (~600 fragments) shows allocator/syscall in the top 10 hot frames, revisit. Otherwise close as no-op.References
docs/superpowers/specs/2026-05-21-f3-f6-download-optimization-design.md(F4 dropped after research)docs/superpowers/specs/2026-05-04-download-optimization-audit.md(F4 section)