In any Introduction level CosmosDB talk, Presenter will suggest you pay more attention to the Partitioning part of the talk. Microsoft wants you to create great solution by using Azure CosmosDB and there are a lot of resources out there for developers. The challenge in Azure CosmosDB is, you don’t need a DBA in CosmosDB and developers may not pay attention to details like Partitioning when they create databases in Azure CosmosDB.
It is crucial to pick the right partition key for your databases in CosmosDB simply because you cannot repartition your databases. If you pick a wrong partition key for your data model, it will be simply too late to change it later. You might have good amount of data in your databases, that means you spent good amount of RU to insert this data and only way to fix this problem will be start from scratch and upload all data back again to CosmosDB with the right partition key.
Read on for a couple of analogies and why this is so important.