Storage Structures

The IBM® i product is an object-based system. All database objects in Db2® for i (tables and indexes for example) are objects in the IBM i operating system. The single-level storage manager manages all storage of objects of the database, so database specific storage structures (for example, table spaces) are unnecessary.

A distributed table allows data to be spread across different database partitions. The partitions included are determined by the nodegroup specified when the table is created or altered. A nodegroup is a group of one or more IBM i products. A partitioning map is associated with each nodegroup. The partitioning map is used by the database manager to determine which system from the nodegroup will store a given row of data. For more information about nodegroups and data partitioning see the DB2® Multisystem book.

A table can also include columns that register links to data that are stored in external files. The mechanism for this is the DataLink data type. A DataLink value which is recorded in a regular table points to a file that is stored in an external file server.

The DB2 File Manager on a file server works in conjunction with DB2 to provide the following optional functionality:

• Referential integrity to ensure that files currently linked to DB2 are not deleted or renamed.
• Security to ensure that only those with suitable SQL privileges on the DataLink column can read the files linked to that column.

The DataLinker comprises the following facilities:

DataLinks File Manager

Registers all the files in a particular file server that are linked to DB2.

DataLinks Filter

Filters file system commands to ensure that registered files are not deleted or renamed. Optionally, filters commands to ensure that proper access authority exists.