multi-master in cosmosdb/documentdb

Question

How can I set up multiple write regions in cosmosdb so that I do not need to combine query results of two or more different regions in my application layer? From this documentation, it seems like cosmosdb global distribution is global replication with one writer and multiple read secondarys, not true multi-master. https://docs.microsoft.com/en-us/azure/documentdb/documentdb-multi-region-writers

Answer 1

As of May 2018, Cosmos DB now supports multi-master natively using a combination of CRDT data types and automatic conflict resolution.

Multi-master in Azure Cosmos DB provides high levels of availability (99.999%), single-digit millisecond latency to write data and scalability with built-in comprehensive and flexible conflict resolution support.

Multi-master is composed of multiple master regions that equally participate in a write-anywhere model (active-active pattern) and it is used to ensure that data is available at any time where you need it. Updates made to an individual region are asynchronously propagated to all other regions (which in turn are master regions in their own). Azure Cosmos DB regions operating as master regions in a multi-master configuration automatically work to converge the data of all replicas and ensure global consistency and data integrity.

Azure Cosmos DB implements the logic for handling conflicting writes inside the database engine itself. Azure Cosmos DB offers comprehensive and flexible conflict resolution support by offering several conflict resolution models, including Automatic (CRDT- conflict-free replicated data types), Last Write Wins (LWW), and Custom (Stored Procedure) for automatic conflict resolution. The conflict resolution models provide correctness and consistency guarantees and remove the burden from developers to have to think about consistency, availability, performance, replication latency, and complex combinations of events under geo-failovers and cross-region write conflicts.

More details here: https://docs.microsoft.com/en-us/azure/cosmos-db/multi-region-writers

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Answer 2

According to your supplied link, based on my understanding. Multi-master in cosmosdb/documentdb is implemented by multiple documentdbs separately for write regions and read the documents from the combined query. Currently it seems that it is not supported to set up multiple write regions in cosmosdb so that don't need to combine query results of two or more different regions .