partial update on cosmos db

Question

Hi all,

I have a few data sources which going to write into a single cosmos db container based on the id but the the update will be on different fields.

Example. the document json will be like

{id: xxxx, car_number:xxx, car_model:xxx, car_color:xxx, datetime:xxx} (please ignore the syntax error)

My data source A will have id, car_number.

My data source B will have id, car_model.

My data source C will have id, car_color.

In a particular time all the data sources are sending data for the same id which mean concurrent write is happening.

Is there any special handling is required when using the partial document update method in cosmos db to handle concurrent write or it will be handled internally by cosmos in the backend?

Thanks in advance!

Answer 1

Thanks for posting your question in the Microsoft Q&A forum.

In Cosmos DB, concurrent writes to the same document can be handled using optimistic concurrency control (OCC). This means that when you perform a partial document update, Cosmos DB checks the document's _etag value to ensure that no other write operation has modified the document since it was read. If the _etag value does not match, indicating that the document has been modified, Cosmos DB will return a 412 (Precondition Failed) status code, and you can handle the conflict accordingly.

https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/database-transactions-optimistic-concurrency

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