GitNexus/gitnexus/bench/emit-persistence

Emit-persistence bench (#2203)

Build-free throughput + byte-identity guard for the CSV-generation half of the graph-DB persistence pipeline (streamAllCSVsToDisk), which dominates large-repo analyze wall time alongside parsing (issue #2203).

# from gitnexus/
node --import tsx bench/emit-persistence/measure.mjs           # print one JSON line
node --import tsx bench/emit-persistence/measure.mjs --check    # gate vs baselines.json

What it measures

A synthetic KnowledgeGraph (files + functions + classes + 4 edge types across the File→Function, File→Class, Function→Function label pairs) at two scales:

• elapsed_ms_small / elapsed_ms_large — median wall-clock over REPS runs of streamAllCSVsToDisk.
• scaling_ratio — (t_large/t_small)/(LARGE/SMALL); ~1.0 is linear. The --check gate fails if it exceeds scaling_budget (catches an O(n²) re-regression in the emit/routing path).
• fingerprint — order-independent sha256 over every emitted CSV line (node CSVs + per-FROM→TO-label-pair rel CSVs). This is the byte-identity gate: the U2 (direct per-pair routing) and U3 (per-row microtask elimination) optimisations must not change graph content, and any future change that does fails --check. Byte-identity holds for all quote-free ids; for an id containing a " the router intentionally diverges from — and is more correct than — the legacy regex oracle (see src/core/lbug/rel-pair-routing.ts).

What it does NOT measure

• The LadybugDB COPY half. Bulk loading needs a live writable DB connection, so it can't run build-free. Its per-stage timing lives in the runtime PROF_LBUG_LOAD=1 breakdown ([lbug-load prof] csv-emit=… copy-nodes=… copy-rels=… fallback=… total=…) and is exercised end-to-end by the integration round-trip tests (test/integration/basicblock-roundtrip.test.ts, lbug-core-adapter.test.ts).
• Content extraction. Bench nodes have no backing source files, so the content column is empty — emit cost here reflects the CSV machinery (routing, escaping, buffering, disk writes), not file reads.
• At-scale absolute numbers. The real postgres / kernel-fs/ wall (issue #2203's table) is a maintainer-run measurement; this synthetic bench is the reproducible regression guard, not a substitute for those runs.

Deferred follow-up

Parallelising the COPY loop (PARALLEL=false is load-bearing; LadybugDB is single-writer) is out of scope for #2203 pending empirical validation of concurrent-COPY support — the PROF_LBUG_LOAD breakdown is the prerequisite that shows whether COPY is the dominant cost worth that risk.

Regenerating the baseline

node --import tsx bench/emit-persistence/measure.mjs    # copy fingerprint + ratio into baselines.json