# Idempotent Requests and Concurrent Updates

*MuleSoft Platform Architect Study Guide · Designing and sharing APIs · Last updated November 13, 2026 · https://www.certifyforce.com/study-guide/mulesoft-platform-architect/designing-and-sharing-apis/idempotent-requests-and-concurrent-updates*

Separate safe reads, repeatable request effects and conditional updates. Use HTTP validators to distinguish existence checks, lost-update protection and cache revalidation.

- Certification: Salesforce MuleSoft Platform Architect
- Exam section: Designing and sharing APIs
- Study guide: https://www.certifyforce.com/study-guide/mulesoft-platform-architect

**Official exam objective:**

> Identify idempotent HTTP methods and HTTP-native support for optimistic concurrency.

## What the exam expects

- Identify HTTP methods with safe and idempotent semantics.
- Distinguish repeatable server effects from identical responses.
- Choose a representation-version precondition or an existence precondition.
- Apply strong comparison when evaluating If-Match.
- Separate conditional updates from cached-response validation.

**Safe** means the client requests read-only behavior; **idempotent** means repeating an identical request has the same intended server effect; an **ETag** identifies a representation version; a **precondition** limits when a method proceeds; **optimistic concurrency** checks for conflicting changes rather than holding a lock across client work.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Safe methods | GET and HEAD request retrieval without an intended state change. | [Idempotent](https://developer.mozilla.org/en-US/docs/Glossary/Idempotent) |
| PUT and DELETE | Idempotent under their HTTP semantics; not safe reads. | [Idempotent](https://developer.mozilla.org/en-US/docs/Glossary/Idempotent) |
| POST and PATCH | Have no method-level idempotency guarantee. | [Idempotent](https://developer.mozilla.org/en-US/docs/Glossary/Idempotent) |
| Repeated response | Can differ while the intended effect remains idempotent. | [Idempotent](https://developer.mozilla.org/en-US/docs/Glossary/Idempotent) |
| If-Match comparison | Uses strong comparison; weak tags do not match. | [If-Match](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/If-Match) |
| Existence-only condition | If-Match wildcard requires a current representation. | [RFC 9110](https://www.rfc-editor.org/rfc/rfc9110.html#section-13.1) |
| Cached representation | Send its ETag in If-None-Match for revalidation. | [ETag](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/ETag) |
| Validator construction | Generation algorithm and quoted field syntax are distinct. | [ETag](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/ETag) |

## Check yourself

- Why should a client avoid assuming that every ETag encodes one mandatory hash algorithm?
- When transmitting an entity tag, how is its opaque value delimited?
- Which alternative forms can construct an If-Match field without mixing them?

## Sources

- [Idempotent — MDN Glossary](https://developer.mozilla.org/en-US/docs/Glossary/Idempotent)
- [ETag header — MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/ETag)
- [If-Match header — MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/If-Match)
- [HTTP Semantics — RFC 9110 Conditional Requests](https://www.rfc-editor.org/rfc/rfc9110.html#section-13.1)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 6 linked practice questions, and unlimited timed mock exams are included with the MuleSoft Platform Architect pack (USD $19): https://www.certifyforce.com/practice-exams