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Figure 68 Relational database
Figure 68 on page 238 shows a typical relational database with the structures
described below.
Data files are physical files that contain all of a database’s data. They change
randomly and can be very large. They are internally divided into pages.
Transaction logs record all database transactions before they are further processed.
Should a failure prevent modified data from being permanently written to data files,
the changes can be obtained from log files. Any kind of recovery is done in two
parts: roll forward, which applies transaction changes into the main database and
roll back, which removes uncommitted transactions.
Control files hold information about the physical structure of the database, such as,
database names, names and locations of a database’s data files and log files, and
the time stamp of the database’s creation. This control data is kept in control files.
These files are critical for the operation of the database-
The cache of the database server process contains the most-often used pages of the
data files.
The following is the standard flow of transaction processing:
Integration with database applications238