Ensuring Idempotency in High‑Concurrency Systems: Strategies and Best Practices

During system development, duplicate inserts, updates, or message retransmissions often occur due to complex business logic and network uncertainty; certain operations, like order creation, must be idempotent to avoid severe consequences.

System's idempotency

Idempotency is a concept where performing an operation N times yields the same result as performing it once.

How to guarantee idempotency in high‑concurrency systems

1. Query

Read‑only APIs are naturally idempotent because querying once or multiple times does not change any data.

2. MVCC solution

Multi‑Version Concurrency Control with conditional updates (optimistic locking) uses a version field or other conditions to ensure safe updates under concurrency.

update table_xxx set name=#name#, version=version+1 where version=#version#

update table_xxx set quality=quality-#subQuality# where quality-#subQuality# >= 0

3. Separate deduplication table

When many business documents need deduplication (e.g., in ERP systems), a dedicated deduplication table can be used; inserting into it leverages the database's unique index to enforce uniqueness.

4. Distributed lock

In distributed systems where a unique key is hard to define, a third‑party distributed lock can be acquired before inserting or updating data, ensuring only one instance performs the operation.

5. Delete operation

Deletion can be made idempotent by treating the first delete as the actual operation; subsequent delete attempts simply return success without affecting data.

6. Unique index on insert

Business‑level primary keys can be constrained with a unique index; for example, three fields together guarantee uniqueness, and the database enforces it.

API‑level idempotency can be achieved by adding a unique identifier (e.g., UUID) to the request payload; the server uses this identifier to detect and ignore duplicate submissions.

7. State‑machine idempotency

When business documents or tasks follow a finite state machine, once a document reaches a later state, attempts to revert to an earlier state are rejected, preserving idempotency.

Source: http://www.cnblogs.com/moonandstar08/p/5334865.html