A Cosmos DB item was read with an ETag. How do you implement optimistic concurrency control?

1. A Use a stored procedure
2. ✓ B Use If-Match header with the ETag on the update request (correct answer)
3. C Use partition key locking
4. D Use transaction batch with read-first

Shortcut: Cosmos DB supports optimistic concurrency via ETags. Include the If-Match header with the item's ETag on updates; if the item was modified since, Cosmos DB returns 412 Precondition Failed.