<t>Honestly the video here* was a MAJOR help to understanding partitioning in CosmosDb.<br/>
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But, in a nutshell:<br/>
The PartitionKey is a property that will exist on every single object that is best used to group similar/related objects together.<br/>
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Good examples include Location (like City), Customer Id, Team, and more. Naturally, it wildly depends on your solution; so perhaps if you were to post what your object looks like we could recommend a good partition key.<br/>
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EDIT: Should be noted that PartitionKey isn't required for collections under 10GB. (thanks David Makogon)<br/>
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- The video used to live on this MS docs page entitled, "Partitioning and horizontal scaling in Azure Cosmos DB", but has since been removed. A direct link has been provided, above.</t>
