Physical Design: Clustering
When an object becomes persistent, by default it is clustered near its parent
DBA can specify clusters based on cluster trees:
- subsets of the schema composition graph
- can be sorted
- defined on classes or collection objects
- deep cluster trees can impede performance
Examples:
- cluster Person /* all Person objects clustered */
- cluster Department on (chair) /* Departments stored with chairs; emps, majors stored elsewhere */