Definition
Idempotency
Idempotency is the property that performing an operation multiple times produces the same result as performing it once. A request that charges a card or creates a record is made idempotent by attaching a unique key, so that retries from network failures or duplicate sends don't cause double charges or duplicate data — essential for reliable distributed systems.
Key takeaways
- Idempotency means performing an operation many times yields the same result as performing it once.
- It's implemented with an idempotency key: the server stores the first result and returns it for any repeat of the same key.
- It makes retries safe in distributed systems, preventing double charges or duplicate records after network failures.
- GET, PUT, and DELETE are idempotent by definition; POST is not, so creation endpoints need explicit idempotency keys.
In a distributed system, a client that sends a request and gets no response can't tell whether the request succeeded, failed, or is still in flight. The safe instinct is to retry — but if the original actually succeeded, a naive retry double-charges the customer or creates a duplicate order. Idempotency solves this by making repeated identical operations safe: the second attempt has no additional effect.
The common implementation is an idempotency key — a unique identifier the client generates and attaches to a request. The server records the key with the result of the first execution; if a request arrives with a key it has already processed, the server returns the stored result instead of executing again. The client can now retry freely until it gets a definitive answer.
Idempotency also describes HTTP method semantics: GET, PUT, and DELETE are defined as idempotent (repeating them lands in the same state), while POST is not, which is why creation endpoints need explicit idempotency keys. The same principle underlies reliable message processing, webhook delivery, and the outbox pattern, all of which assume messages may arrive more than once.
Planoda builds idempotency into its write paths and webhook delivery — events carry stable identifiers and the transactional outbox guarantees at-least-once delivery without duplicate side effects, so consumers can safely retry.
Related terms
- Transactional OutboxThe transactional outbox is a reliability pattern that guarantees a side effect — a webhook, an event, a notification — fires exactly when its database change commits, and never otherwise. The action is written to an outbox table inside the same transaction as the data change, then a separate process delivers it, eliminating the lost or phantom events that plague naive 'save then send' code.
- WebhookA webhook is an automated HTTP request a system sends to a URL you provide whenever a specified event occurs — an issue created, a status changed, a comment added. Instead of repeatedly polling an API for changes, your service receives a real-time push. Webhooks are the backbone of integrations, letting tools react to each other instantly.
- Multi-TenancyMulti-tenancy is an architecture where one running application and database serve many independent customers (tenants), with each tenant's data strictly isolated from the others. It lets a SaaS product share infrastructure for efficiency while guaranteeing that one workspace can never see another's data — a guarantee enforced in the data layer, not left to hope.
- Audit TrailAn audit trail is an append-only, time-ordered record of who did what, when, and to which object across a system. Every create, edit, delete, and approval is logged immutably, so any state can be traced back to the actions that produced it. Audit trails underpin accountability, debugging, compliance, and — increasingly — oversight of what AI agents do.
- CI/CD (Continuous Integration / Continuous Delivery)CI/CD is the practice of automatically building, testing, and releasing code through a pipeline triggered by every change. Continuous integration merges and verifies work frequently to catch conflicts early; continuous delivery keeps the software always in a releasable state, often deploying automatically. Together they shorten the path from a commit to running in production.