Composite Partition Functions

Composite partition function techniques are described herein that may be used to repartition a database without moving existing data. In one or more implementations, a database is partitioned in a first arrangement associated with a first partition function. The database is repartitioned to form a second arrangement associated with a second partition function. A record of key membership for data entries in the partitions existing at the time of repartitioning is created, which can be used to recognize data corresponding to the first arrangement. A composite partition function is defined for subsequent database operations that is configured to apply the first partition function for data having keys found in the record of key membership and apply the second partition function for other data having keys that are not found in the record of key membership.