# Effect is not BEAM

> 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).

BEAM processes isolate their state. Supervision observes worker failure and applies restart policy. Restart still loses volatile state.

> Shared-nothing concurrency ensures complete isolation between processes: one process can’t compromise the internal state of another.

Source: [Q03](/lore/durability-bibliography#q03); [B1](/lore/durability-bibliography#b1-erlang-and-otp-in-action), [B2](/lore/durability-bibliography#b2-elixir-in-action), [B3](/lore/durability-bibliography#b3-designing-elixir-systems-with-otp).

## Failure it prevents

A failed computation has already changed shared state, while the caller assumes process isolation.

## Our Effect 4.0.0 reading

[Scope](/lore/scopes-own-resources) and `FiberSet` own local lifetimes. They do not supply separate heaps or OTP restart strategies. Use a host boundary for hard isolation.

Source: `packages/effect/src/Scope.ts`, `packages/effect/src/FiberSet.ts`, `packages/effect/src/Fiber.ts`.

## How to check

State which failure the boundary contains. Test a worker [defect](/lore/effect-basics) and a hard runtime exit separately. This check is our proposal. The books do not prescribe it.

Continue with [Supervision chooses what restarts](/lore/supervision-is-a-recovery-policy), [Durable work needs storage](/lore/durable-work-needs-storage).

Connect this to [the existing rat-stack guidance](/lore/concurrent-work-needs-an-owner).

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

## Sources

1. [Logan, Martin; Merritt, Eric; Carlsson, Richard. Erlang and OTP in Action.](https://www.manning.com/books/erlang-and-otp-in-action)
   Manning. The Erlang/OTP Platform: Let It Crash; process isolation; §4.2.2 supervisor restart strategy. Accessed 2026-10-23.

2. [Jurić, Saša. Elixir in Action, Third Edition. Manning, 2024.](https://www.manning.com/books/elixir-in-action-third-edition)
   Manning. §5.4.3 Shared-Nothing Concurrency; Chapters 8–9, fault tolerance and supervision; Other Use Cases for ETS. Accessed 2026-10-23.

3. [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.

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

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

## Lore on this page

- [Supervision chooses what restarts](/lore/supervision-is-a-recovery-policy)

## Linked from

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

- Bulkheads isolate scarce capacity → Reserve independent capacity for workloads that must not starve each other. → [Read page](https://ratstack.sh/lore/bulkheads-isolate-capacity)

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

- 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 bibliography → Books, checked short quotations, source limits, and Effect mapping provenance. → [Read page](https://ratstack.sh/lore/durability-bibliography)

- 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)

- 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)