Best practices for handling concurrent updates in DynamoDB

In distributed systems, multiple processes or users may attempt to modify the same data at the same time. Without concurrency control, these concurrent writes can lead to lost updates, inconsistent data, or race conditions. DynamoDB provides several mechanisms to help you manage concurrent access and maintain data integrity.

Note

Individual write operations such as UpdateItem are atomic and always operate on the most recent version of the item, regardless of concurrency. Locking strategies are needed when your application must read an item and then write it back based on the read value (a read-modify-write cycle), because another process could modify the item between the read and the write.

There are two primary strategies for handling concurrent updates:

• Optimistic locking – Assumes conflicts are rare. It allows concurrent access and detects conflicts at write time using conditional writes. If a conflict is detected, the write fails and the application can retry.

• Pessimistic locking – Assumes conflicts are likely. It prevents concurrent access by acquiring exclusive access to a resource before modifying it. Other processes must wait until the lock is released.

The following table summarizes the approaches available in DynamoDB:

Approach	Mechanism	Best for
Optimistic locking	Version attribute + conditional writes	Low contention, inexpensive retries
Pessimistic locking (transactions)	TransactWriteItems	Multi-item atomicity, moderate contention
Pessimistic locking (lock client)	Dedicated lock table with lease and heartbeat	Long-running workflows, distributed coordination

Choosing a concurrency control strategy

Use the following guidelines to choose the right approach for your workload:

Use optimistic locking when:

• Conflicts are infrequent.

• Retrying a failed write is inexpensive.

• You are updating a single item at a time.

Use transactions when:

• You need to update multiple items atomically.

• You require all-or-nothing semantics across items or tables.

• You need to combine condition checks with writes in a single operation.

Use the lock client when:

• You need to coordinate access to external resources across distributed processes.

• The critical section is long-running and retrying on conflict is expensive.

• You need automatic lock expiry to handle process failures.

Note

If you use DynamoDB global tables, be aware that global tables use a "last writer wins" reconciliation strategy for concurrent updates. Optimistic locking with version numbers does not work as expected across Regions because a write in one Region may overwrite a concurrent write in another Region without a version check. Design your application to handle conflicts at the application level when using global tables.