# Bulkheads isolate scarce capacity

> For agents: start with the [agent guide](https://ratstack.sh/llms.txt). Every page is Markdown by default; add `Accept: text/html` for HTML.

Free workshop: [Build Agent Loops That Never Stop Shipping](/tokenmaxx#interested).

Critical clients need their own capacity. A single shared limit can still let one failed or noisy workload consume every available slot.

> Protect critical clients by giving them their own pool to call.

Source: [Q07](/lore/durability-bibliography#q07); [B4](/lore/durability-bibliography#b4-release-it), [B3](/lore/durability-bibliography#b3-designing-elixir-systems-with-otp).

## Failure it prevents

Noncritical load exhausts the pool needed by the primary path.

## Our Effect 4.0.0 reading

Separate `Semaphore` or `Queue` instances isolate local work admission. `Pool` manages actual resources. Independent runtime or infrastructure failure domains require more than fibers.

Source: `packages/effect/src/Semaphore.ts`, `packages/effect/src/Queue.ts`, `packages/effect/src/Pool.ts`.

## How to check

Saturate one workload. Confirm that the separately reserved critical path still acquires its resources. This check is our proposal. The books do not prescribe it.

Continue with [Backpressure reaches the producer](/lore/backpressure-reaches-the-producer), [Effect is not BEAM](/lore/effect-is-not-beam).

Connect this to [the existing rat-stack guidance](/lore/scopes-own-resources).

Use [the durability skill](/skills/durability) for the full review. Return to [the durability index](/lore/durability).

## Sources

1. [Nygard, Michael T. Release It!: Design and Deploy Production-Ready Software. Pragmatic Bookshelf, 2007.](https://archive.org/details/releaseitdesignd0000nyga)
   Pragmatic Bookshelf. §4.4 Unbounded Result Sets; Chapter 5 Stability Patterns: §5.1 Timeouts, §5.2 Circuit Breaker, §5.3 Bulkheads, §5.4 Steady State, §5.5 Fail Fast, §5.6 Handshaking, §5.7 Test Harness, §5.8 Decoupling Middleware. Accessed 2026-10-23.

2. [Gray II, James Edward; Tate, Bruce A. Designing Elixir Systems with OTP. Pragmatic Bookshelf, 2019.](https://pragprog.com/titles/jgotp/designing-elixir-systems-with-otp/)
   Pragmatic Bookshelf. Build a Functional Core; Isolate Process Machinery in a Boundary; Customize Your Lifecycle; Big, Loud Worker-Bees; Add Persistence as a Boundary Service; Test the Boundary. Accessed 2026-10-23.

3. [Effect contributors. Effect 4.0.0. Semaphore.ts](https://github.com/Effect-TS/effect/blob/67ba4e46a11ccda0b6761578bfd22c04ae00167d/packages/effect/src/Semaphore.ts)
   Effect-TS. Pinned source for our Effect mapping, not a claim from the book. Accessed 2026-10-23.

4. [Effect contributors. Effect 4.0.0. Queue.ts](https://github.com/Effect-TS/effect/blob/67ba4e46a11ccda0b6761578bfd22c04ae00167d/packages/effect/src/Queue.ts)
   Effect-TS. Pinned source for our Effect mapping, not a claim from the book. Accessed 2026-10-23.

5. [Effect contributors. Effect 4.0.0. Pool.ts](https://github.com/Effect-TS/effect/blob/67ba4e46a11ccda0b6761578bfd22c04ae00167d/packages/effect/src/Pool.ts)
   Effect-TS. Pinned source for our Effect mapping, not a claim from the book. Accessed 2026-10-23.

## Linked from

- Agent guide → An Effect stack so pure (aspirational) Kit Langton will blush. → [Read page](https://ratstack.sh/llms.txt)

- Backpressure reaches the producer → Bounded consumption helps only when upstream respects waiting or refusal. → [Read page](https://ratstack.sh/lore/backpressure-reaches-the-producer)

- Change log → What changed in the files served here, newest first. → [Read page](https://ratstack.sh/log)

- Circuit breakers have state → A breaker stops doomed calls and controls probes before restoring traffic. → [Read page](https://ratstack.sh/lore/circuit-breakers-have-state)

- durability → Keep a rat-stack app standing when a provider, pool, or dependency slows down or a worker dies. Use at any I/O boundary, connection pool, provider call, shared waiter, fan-out, flag, gate, or work that can outlive a request, or when asked "what happens when this is slow", "add a timeout", "make this durable", or "what survives a crash". → [Read page](https://ratstack.sh/skills/durability)

- Durability starts with a recovery record → A reading order for storage, replay, worker ownership, overload, and recovery tests. → [Read page](https://ratstack.sh/lore/durability)

- Full agent guide → An Effect stack so pure (aspirational) Kit Langton will blush. → [Read page](https://ratstack.sh/llms-full.txt)

- Queries need result bounds → Limit result cardinality before the driver materializes an oversized response. → [Read page](https://ratstack.sh/lore/queries-need-result-bounds)

- Rat Stack lore | rat-stack → Short, source-grounded notes on the ideas and decisions behind rat-stack. → [Read page](https://ratstack.sh/lore)

- Source change history (log.md) → The generated change log as Markdown. → [Read page](https://ratstack.sh/log.md)