1. A method for real-time sharing of resources in a multi-tenant software-as-a-service (SaaS) system, the method comprising: receiving service requests from multiple users belonging to different tenants of the multi-tenant SaaS system; partitioning the resources in the SaaS system into different resource groups, each resource group handling a category of the service requests; estimating costs of the service requests by using a tenant segmentation variable, a segment representing a group of tenants, a tenant representing a group of users, a first multiplication of the tenant segmentation variable and a first regression parameter estimate, a second multiplication of a current workload of the multi-tenant SaaS system and a second regression parameter estimate, an addition of a result of the first multiplication and a result of the second multiplication, and historical cost estimates of prior service requests from each of the users; and dispatching the service requests to the resource groups according to the estimated costs, whereby the resources are shared, among the users, without impacting each other.