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System Architecture 2-81
Disk Data Structures
Disk Data Structures
OnLine achieves its high performance by managing its own I/O. Storage,
search, and retrieval are all managed by OnLine. As OnLine stores data, it
creates the structures it needs to search and retrieve the data later. OnLine
disk structures also store and track control information needed to manage
logging and archiving. OnLine structures must contain all information
needed to ensure data consistency, both physical and logical.
OnLine Disk Space Terms and Definitions
During OnLine operation, either UNIX or OnLine can manage physical disk
I/O. Two terms describe the space:
■ Cooked file space, in which UNIX manages physical disk I/O
■ Raw disk space, in which OnLine manages physical disk I/O
Physical space managed by OnLine is allocated in four different units:
■ A chunk
■ An extent
■ A page
■ A blobpage
Overlying these physical units of storage space, OnLine data is organized
into five conceptual units associated with database management:
■ A blobspace
■ A dbspace
■ A database
■ A tblspace
■ A table