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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →For ordinary client-record editing, start with optimistic concurrency: return a strong ETag when a client record is read, require the matching value in If-Match on updates, and reject the write if the record has changed. Use exclusive database coordination when a workflow truly requires a resource to be reserved or changes to be serialized. The crucial caveat: an HTTP header prevents lost updates only if the server actually compares it with the current version as part of the write.
Why concurrency control matters
Suppose two staff members load the same client record. One updates the phone number while the other changes the account status. If the second update blindly replaces the full record, it can erase the first person’s change. This is a lost update: both users worked from valid data, but one write silently overwrote newer state.
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Concurrency control gives the API a way to detect or prevent that collision. For the common case where people edit records independently and conflicts can be reconciled, conditional updates are usually the practical starting point. Exclusive coordination is better reserved for short workflows where concurrent operations cannot safely proceed independently.
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Optimistic updates versus exclusive coordination
| Decision | Optimistic conditional update | Pessimistic lock or serialization |
|---|---|---|
| How it handles a conflict | Clients work concurrently; the server checks the submitted version at write time and rejects stale state. | The operation acquires exclusive coordination first; other operations may wait or fail. |
| Good fit | Routine record editing where conflicts are relatively uncommon and a user or client can resolve one. | Short critical workflows where concurrent changes cannot safely proceed independently. |
| Main cost | The client must handle the conflict and reconcile changes. | Waiting, contention, lock lifecycle, and risks from long-held transactions. |
| HTTP expression | A strong ETag with If-Match expresses a conditional state change. |
HTTP does not prescribe the database lock policy; the application and persistence layer must define it. |
The right choice depends on the workflow’s correctness requirements, not merely on whether the API uses REST. Protocol standards define conditional-request behavior; they do not establish a workload’s conflict rate or an ideal retry policy.
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How ETag and If-Match prevent stale writes
RFC 9110 defines If-Match as a request condition: the server performs the method only if the current representation matches one of the supplied entity tags. It requires strong comparison, and the standard describes its common use with state-changing methods to prevent accidental overwrites when user agents act in parallel. A weak ETag is not a substitute for a strong write validator. See RFC 9110, HTTP Semantics.
- Read: The client requests
GET /clients/123. The server returns the representation with a strong ETag, for example"v17". - Edit: A user changes the record while the application retains the ETag associated with the version they saw.
- Submit conditionally: The client sends a suitable
PUTorPATCHwithIf-Match: "v17". - Check and write: The server compares the supplied tag with the current version and applies the change only if they match.
- Handle a stale tag: If the resource has changed, the server does not apply the requested method and can return
412 Precondition Failed. The client reloads current state and helps the user reconcile it with their edits.
"v17" is an illustrative tag, not a prescribed format. The version comparison and write need to be atomic in the persistence layer. If the server checks the version separately and then writes later, two concurrent requests could both pass before either changes the record, defeating the precondition’s purpose.
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When PATCH needs a base version
Use a conditional request when a patch depends on a known base point. RFC 5789 notes that PATCH is not inherently safe or idempotent and recommends conditional requests when a patch depends on a known base representation. See RFC 5789, PATCH Method for HTTP.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesThe patch’s meaning matters. Setting a field to a specific value may behave differently on repetition from incrementing a counter or appending a note. Do not infer that a PATCH is safe to replay merely from its method name; define the operation’s semantics and its version condition deliberately.
Handle retries separately from version conflicts
A lost response creates a different problem from a stale write. The client may not know whether the server applied its request before the connection failed. RFC 9110 defines idempotence by the intended effect of repeating a request: PUT and DELETE are idempotent by HTTP semantics, so a repeat has the same intended effect even if its response differs. The RFC says a client should not automatically retry a non-idempotent request unless it can establish that the original was not applied or otherwise knows repetition is safe. See RFC 9110, HTTP Semantics.
A version precondition does not guarantee exactly-once execution. For actions such as incrementing a balance, creating a note, or sending an invitation, consider application-level idempotency or a way to inspect the resulting state before retrying. There is no universal idempotency-key header or retention period established here as a standard requirement; document the behavior your API implements.
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When database locking or serialization is warranted
Choose exclusive coordination when correctness requires reserving a resource or serializing a critical operation, rather than simply detecting that two editors used the same version. Keep the protected database transaction short and centered on the actual operation. Do not keep a transaction or row lock open while someone considers or edits a form.
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PostgreSQL’s 9.3 concurrency-control documentation discusses advisory locks as one way to emulate pessimistic locking and warns against holding transactions open for long periods, such as while waiting for user input. This is conceptual background from that version’s manual, not current, version-specific syntax guidance: PostgreSQL 9.3, Chapter 13: Concurrency Control.
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Verify the deployed API really enforces the condition
Sending If-Match is not proof that a framework performs per-record version checks. Microsoft Learn documents a Data API builder REST behavior in which per-record ETag or version matching is not implemented; in that described behavior, If-Match: * only asserts that a record exists. Check the specific version and endpoint you deploy, and test whether an old exact tag is rejected: Microsoft Learn: Use the If-Match HTTP Header in PUT and PATCH Operations.
Define what happens if a client omits the condition. If lost updates are unacceptable for an operation, require the precondition rather than silently accepting an unguarded write. The status code and compatibility policy for missing conditions are API design decisions; document them alongside the failed-precondition response.
Quick Recap
Implementation checklist
- Identify which records and state-changing operations need stale-write protection.
- Return a strong ETag or another explicit version token on reads.
- Require
If-Matchfor protected updates; do not treatIf-Match: *as an exact version comparison. - Compare the submitted token and perform the write atomically.
- Return
412 Precondition Failedfor a failed precondition and document the response. - Give clients a clear reload and reconciliation path that preserves a user’s unsaved edits.
- Keep transactions short and reserve exclusive locks for operations that need them.
- Document retry behavior separately for idempotent and non-idempotent operations.
- Test a stale update against the deployed service, not just a local framework assumption.
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