A database management system may be operated by a third-party provider that hosts the system in a datacenter and provides access to the system to end users on behalf of various entities. Limits on total capacity consumption may be imposed, but may result in service outages when capacity consumption exceeds those limits. Requests to perform operations on the system may be classified. The request classifications may be associated with policies for admitting or rejecting the request. One or more token buckets representative of capacity available to the request to perform the operation may be used to determine to admit the request and updated based on the cost of performing the operation.
