> ## Documentation Index
> Fetch the complete documentation index at: https://filament.getgalaxy.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Event Bus Publish Overhead

> Publish cost with no subscribers, fan-out, and contention.

Defined in `eventbus/inproc/inproc_bench_test.go`, against the in-process
event bus implementation.

## `BenchmarkPublishNoSubscribers`

The floor: publish overhead with nothing listening — sequencing, the bounded
log, subject splitting, and the subscriber match loop, with no fan-out cost.
The log is capped (`WithMaxLog(4096)`) so memory stays flat across
iterations.

```sh theme={"theme":"vitesse-black"}
go test -bench=BenchmarkPublishNoSubscribers -benchmem ./eventbus/inproc/...
```

## `BenchmarkPublishFanout8`

Adds 8 draining subscribers on a wildcard subject (`app.v1.>`) — the
realistic per-fact cost once the control plane and any listeners are
actually receiving events, rather than the theoretical floor above.

```sh theme={"theme":"vitesse-black"}
go test -bench=BenchmarkPublishFanout8 -benchmem ./eventbus/inproc/...
```

## `BenchmarkPublishParallel`

Concurrent publishers contending on the bus's single mutex, with 4 drained
subscribers so the match loop also runs under the lock — this is the one
that shows contention cost as publishers scale, using Go's `RunParallel`.

```sh theme={"theme":"vitesse-black"}
go test -bench=BenchmarkPublishParallel -benchmem ./eventbus/inproc/...
```