feat(asap-tools): add paced feeder for the data-plane eval

[zzylol]

Summary

Adds asap-tools/data-sources/paced-feeder, the data feeder for the data-plane vs ClickHouse evaluation (#789). It generates the synthetic workload on the fly and sends it in real time, one second of event time per wall-clock second:

• ASAPQuery: Prometheus remote write to /api/v1/write (snappy-compressed protobuf).
• ClickHouse: INSERT … FORMAT RowBinary into (ts DateTime64(3), label_0 String, instance String, value Float64).

The data has C groups (label_0) × s series per group (instance), --samples-per-sec samples per series, and Pareto(shape, scale) values. Each value is a stateless hash of (seed, series, sample index), so two feeders with the same flags send identical data and no dataset file is needed. At 1e6 series × 900 s, a file would be about 9e8 rows (~50 GB) per workload.

Pacing. Each tick is split into batches sent concurrently, and the next tick waits for all of them, so a series' samples never arrive out of order. --stats-out writes per-tick rows, bytes, start lag and elapsed time, plus achieved_rows_per_sec, overrun_ticks and errors. Any failed request makes the feeder exit non-zero.

Batch sizes. The default batch size depends on the sink. Remote write uses 50,000 rows, which compresses to about 0.76 MB per request, under axum's 2 MB default body limit in ASAPQuery's ingest. ClickHouse uses 100,000 rows: at 50,000 rows, 1e6 rows/s fell behind (ticks took about 1.15 s, since each INSERT creates a part).

It is a standalone crate (empty [workspace], own Cargo.lock), like otlp_exporter and fake_exporter.

Testing

• Unit tests (6):
  • every series gets a sample in each sub-second slot of a tick;
  • values depend only on seed, series and sample index;
  • series map to the right group and instance labels;
  • values follow the Pareto distribution (empirical vs theoretical p50/p90/p99 within 5%);
  • remote write decodes, with structs mirroring prometheus_remote_write.rs, to the right labels (sorted) and samples;
  • RowBinary round-trips every column.
• Live runs on a CloudLab c6320, against ClickHouse 26.10 (single binary) and the precompute_engine binary from main:

Run	Result
ClickHouse, 1e5 rows/s, 10 s	1,000,000 rows; 100,000 distinct series; 10 distinct timestamps; all values ≥ 1; no overruns
ClickHouse, 1e6 rows/s, 10 s, feeder pinned to 2 cores	1e6 rows/s, 0 overruns, feeder 0.15 cores
ASAPQuery remote write, 1e6 rows/s, 10 s, feeder pinned to 2 cores	1e6 rows/s, 0 overruns, 0 failed requests, feeder 0.34 cores. The engine logged the parsed series data{instance="i0",label_0="g0"} routed to the configured aggregation

cargo clippy --all-targets -- -D warnings and cargo fmt --check are clean.

🤖 Generated with Claude Code