Abstract: According to aspects of the disclosure, there is provided a scalable cloud distributed database system for hosting data of multiple database tenants. In some embodiments, the database may be serverless. The serverless database may be configured to automatically and dynamically match resources to workload demands for tenants of the database. Databases described herein may include replica sets hosting multiple tenants. Tenants may be migrated from one replica set to another replica set based on usage. Usage of tenants may be throttled during migration between replica sets. Tenants with lower usage may be selected for migration between replica sets. During migration, files containing both a document and a history of updates to the document may be migrated. Databases described herein may include multiple storage tiers having different read and/or write speeds.