# Pattern Breaks: Why Conventions Are Violated

Based on git archaeology across CockroachDB, Prometheus, Temporal,
Ecto, and Oban. Each category with real examples.

---

## Category 1: Ship Behavior, Fix Plumbing Later

**Example:** CockroachDB bare goroutine in kvadmission

```go
// TODO(irfansharif): Use a stopper here instead.
go func() {
    ticker := time.NewTicker(10 * time.Minute)
    for { select { case <-ticker.C: ... } }
}()
```

**History:** Irfan Sharif, Aug 2022. Part of the elastic CPU limiter
(20+ file change). Complex new admission control system. The author
tagged it with TODO in the SAME commit. Ship the behavior, fix the
plumbing later.

**Why it survives:** Nobody touched the function for any other reason.
The goroutine leaks nowhere (process-lifetime). The TODO is correct
but not urgent.

**For review:** Worth noting, not worth blocking the PR.

---

## Category 2: Better Tooling Exposed the Limitation

**Example:** CockroachDB Handle replacing RunAsyncTask

**History:** Feb 2025, Tobias Grieger. RunAsyncTask was *correct* but
made every goroutine look identical in execution traces. The Handle
pattern was motivated by profiling/observability, not correctness.

**Key quote from PR:** "It becomes an ordeal to search for a specific
goroutine, since all goroutines started by the Stopper get assigned
the same searchable identity."

**For review:** Track it. This is how progress happens.

---

## Category 3: Removal Cost > Carrying Cost

**Example:** CockroachDB stale "Remove in 22.2" TODO

```go
// TODO(ajwerner): Remove in 22.2.
SystemConfigProvider config.SystemConfigProvider
```

**History:** Feb 2022. Bridge for mixed-version clusters during
gossip→span-config migration. A struct field that costs one pointer
of memory. Removing it means touching StoreConfig initialization
across dozens of call sites.

**Why it survives:** Cost of removal >> cost of carrying. The
interest rate on this debt is zero.

**For review:** Leave it alone.

---

## Category 4: Context Needs Different Pattern

**Example:** Prometheus global vars for scrape timestamp tolerance

```go
var ScrapeTimestampTolerance = 2 * time.Millisecond
```

**History:** Started as "experimental, hidden flag" (Oct 2020). Made
public after production showed 10ms tolerance saves real disk space.

**Why a global:** Set once at startup from a command-line flag. Read
thousands of times per second in the scrape loop. Threading a config
struct would add parameters to every hot-path function for a value
that never changes after init.

**For review:** Approve it. This IS the right pattern for this context.

---

## Summary Table

| Category | Response in Review | Example |
|----------|-------------------|---------|
| Time pressure | Note, don't block | kvadmission goroutine |
| Better tooling | Track migration | Handle API |
| Zero-interest debt | Leave alone | Stale version TODOs |
| Different context | Approve | Hot-path globals |