How to do a transaction with two collections on Azure CosmosDB?

In Azure Cosmos DB, transactions can be performed within a single container. Transactions that span multiple containers are not supported natively. However, you can achieve transaction-like behavior across multiple containers by implementing compensating actions or using a two-phase commit pattern.

Here’s an example of how you can achieve a transaction-like behavior across two collections in Azure Cosmos DB using a two-phase commit pattern:

  1. Begin Transaction:
    • Start by initiating the transaction and defining the set of operations that need to be performed across the two collections.
    • Record the intent to perform these operations in a transaction log or in-memory data structure.
  2. Perform Operations:
    • Execute the desired operations across the two collections as part of the transaction. These operations could involve document inserts, updates, or deletes.
  3. Prepare Phase:
    • In this phase, you prepare the collections for the final commit.
    • Within each collection, record a transaction marker or flag indicating that the collections are in the prepare state. This marker helps track the progress of the transaction.
  4. Commit Phase:
    • Once the prepare phase is complete and both collections are ready for commit, initiate the commit phase.
    • Update the transaction marker or flag in each collection to indicate that the collections are ready for the final commit.
    • Apply the changes to the collections, making them permanent and durable.
  5. Completion:
    • After the commit phase is successful, mark the transaction as completed or remove the transaction log from memory.
    • If any step in the prepare or commit phase fails, you can initiate a rollback or compensating actions to undo the changes made in the transaction.

It’s important to note that this approach requires careful handling of failures, retries, and potential conflicts. It may introduce some level of complexity, and it’s essential to consider the specific requirements and limitations of your application.

Alternatively, you can design your data model to minimize the need for transactions across multiple containers by denormalizing or colocating related data within a single container. This can help ensure transactional consistency within a single container, reducing the need for complex distributed transactions.

Remember to evaluate the specific needs of your application and choose the appropriate approach to achieve the desired transaction-like behavior across multiple collections in Azure Cosmos DB.

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