System Architecture 2-85
OnLine Disk Space Terms and Definitions
Database
Adatabase resides in the dbspace named in theSQL statement CREATE
DATABASE. If no dbspace is specified, the database resides in the root
dbspace. When a database is located in a dbspace, it means two things:
■The database system catalog tables are stored in that dbspace.
■That dbspace is the default location of tables that are not explicitly
created in other dbspaces.
Users create a table by executing theSQL statement CREATE TABLE. A table
resides completely in the dbspace specified in theSQL statement. If no
dbspace is specified, the table resides in the same dbspace as its database.
Blob data associated with the table can reside either in the dbspace with the
rest of the table data or in a separate blobspace.
Tblspace
The total of all disk space allocated to a table is that table’stblspace. The
tblspace includes the following pages:
■Pages allocated to data
■Pages allocated to indexes
■Pages used to store blob data in the dbspace (but not pages used to
store blob data in a separate blobspace)
■Bit-map pages that track page usage within the table extents
Thepages that belong to the tblspace are allocated as extents. Extents can be
scatteredthroughout the dbspace where the table resides. For this reason, all
pages that compose the tblspace are not necessarily contiguous within the
dbspace.
Multiple tblspaces can reside in a single dbspace.
Extent
As more rows of data or indexes are added to a table, OnLine allocates disk
spaceto a table in units of physically contiguous pages called extents. The first
extent allocated to a table is theinitial extent. Each subsequent extent is
referred to as anext extent.