1. A self managing database system, comprising: a database; a server system that provides access to the database for a plurality of user systems, wherein the server system is configured to run: a statistics repository module configured to automatically and periodically collect and compute performance statistics of the database; a plurality of self-management components, each self-management component configured to self-manage an aspect of the database's functionality, wherein the plurality of self-management components include: a SQL management module configured to interact with a SQL tuning advisor module and a SQL access advisor module to tune SQL statements; a memory management module configured to automatically resize shared memory components based on characteristics of a current workload, the shared memory components including a shared pool and a buffer cache; a back-up management module configured to automatically manage backup operations; a disk storage management module configured to automatically distribute I/O loads across disk storage devices; and an object space management module configured to interact with a segment advisor to automatically manage sizes of segments in the database; a plurality of infrastructure components configured to interact with one or more self-management components in the plurality of self-management components, the plurality of infrastructure components including an advisory framework component configured to provide a uniform interface for accessing and receiving information from a plurality of different advisory modules; and a central control module configured to automatically analyze statistics from the statistics repository module and interact with the plurality of self-management components and the plurality of infrastructure components to facilitate execution of at least one of a plurality of database performance enhancement operations, wherein possible database performance problems are categorized according to a rules hierarchy comprising a plurality of nodes, each node in the plurality of nodes being associated with one or more rules, and one or more conditions for satisfying the one or more rules, and wherein the step of automatically analyzing statistics from the statistics repository module includes analyzing the statistics in view of the rules hierarchy to determine a root performance problem.