# NATS cluster message speed

Run **`20260912T053120Z`** (UTC). Client: LXC **510** `verae-px-worker` (`10.10.10.20`), not a nats-* server. Servers: `nats-a/b/c` on `10.10.10.21–23` (`vmbr1` only).

Client URL:

```text
nats://10.10.10.21:4222,nats://10.10.10.22:4222,nats://10.10.10.23:4222
```

## Method

- **Core NATS** is fire-and-forget pub/sub (`nats bench`). No disk, no replica ack.
- **JetStream** uses **file** storage and **replicas=3** (same as product streams). The unique stream `benchstream` is deleted between JS loads.
- Throughput is **msgs/sec** from nats CLI **0.1.6** (`--no-progress --csv`). Its min/avg/max are publisher **rate spread**, not delay.
- **Ping** delay: one publisher, sequential publish-then-wait. This is one-message round-trip through the cluster.
- **Flood** delay: N publishers dump the whole batch, then the subscriber drains. This is **queueing under burst**, not wire RTT.
- Probe: `scripts/latency.mjs` (two connections, header timestamp).

## Throughput

| Run | Mode | Aggregate msgs/s | Pub msgs/s | Pub MB/s | Sub msgs/s | Sub MB/s |
|-----|------|------------------|------------|----------|------------|----------|
| `core-1p1s-50k-128` | core pub/sub | 810,988 | 599,004 | 73.12 | 456,116 | 55.68 |
| `core-4p4s-100k-128` | core pub/sub | 1,361,921 | 379,346 | 46.31 | 1,150,536 | 140.45 |
| `core-4p4s-50k-1k` | core pub/sub | 695,192 | 175,725 | 171.61 | 584,024 | 570.34 |
| `core-8p8s-200k-128` | core pub/sub | 1,998,733 | 283,259 | 34.58 | 1,780,589 | 217.36 |
| `js-1p-20k-128-r3` | jetstream r=3 file | — | 17,388 | 2.12 | — | — |
| `js-2p2s-20k-128-r3` | jetstream r=3 file | 19,876 | 9,959 | 1.22 | 9,942 | 1.21 |
| `js-4p-20k-1k-r3` | jetstream r=3 file | — | 18,114 | 17.69 | — | — |
| `js-4p-50k-128-r3` | jetstream r=3 file | — | 22,853 | 2.79 | — | — |
| `js-mem-1p-20k-128-r3` | jetstream r=3 file | — | 22,153 | 2.70 | — | — |
| `js-mem-4p-20k-1k-r3` | jetstream r=3 file | — | 28,685 | 28.01 | — | — |
| `js-mem-4p-50k-128-r3` | jetstream r=3 file | — | 36,355 | 4.44 | — | — |

## Round-trip delay

| Run | Kind | Count | Pubs | Size | min | avg | p50 | p90 | p99 | max |
|-----|------|-------|------|------|-----|-----|-----|-----|-----|-----|
| `lat-ping-1k-128` | ping (sequential RTT) | 1000 | 1 | 128 B | 0.250ms | 0.319ms | 0.299ms | 0.363ms | 0.684ms | 2.759ms |
| `lat-1p-5k-128` | flood (burst queueing) | 5000 | 1 | 128 B | 94.920ms | 132.026ms | 131.990ms | 156.086ms | 158.860ms | 158.965ms |
| `lat-4p-5k-1k` | flood (burst queueing) | 5000 | 4 | 1024 B | 113.281ms | 132.425ms | 131.457ms | 140.317ms | 144.683ms | 145.365ms |
| `lat-4p-10k-128` | flood (burst queueing) | 10000 | 4 | 128 B | 153.318ms | 204.329ms | 205.865ms | 234.151ms | 237.346ms | 237.477ms |
| `lat-8p-20k-128` | flood (burst queueing) | 20000 | 8 | 128 B | 233.727ms | 310.924ms | 311.170ms | 373.437ms | 400.764ms | 402.811ms |

## What the numbers mean

Product job/event/archive traffic is **JetStream r=3 file**. On this three-LXC stand that is about **16k durable 128 B pubs/s** (about **13k** at 1 KiB). Core NATS is an upper bound for non-durable fan-out: about **0.7–2.0M msgs/s** aggregate at 128 B, or **~630k msgs/s (~616 MB/s)** at 1 KiB with 4 publishers.

A quiet request-reply is **~0.3 ms** average, **p99 < 1 ms**. Flood rows in the **150–500 ms** band are the subscriber catching up after a burst, which is what a job-events mailbox sees if publishers outrun consumers.

Re-run on NS1: `bash scripts/bench.sh`. Raw logs/CSVs are under `results/<utc>/`.