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Updates to the control files are insignificant compared to
other disk I/O that occurs in an Oracle environment.
40 | Chapter 2: Oracle Architecture
Datafiles
Datafiles contain the actual data stored in the database, the tables and indexes that
store data, the data dictionary that maintains information about these data structures,
and the rollback segments used to implement concurrency.
A datafile is composed of Oracle database blocks that, in turn, are composed of operating
system blocks on a disk. Oracle block sizes range from 2 KB to 32 KB. Prior to
Oracle9i, only a single block size could be present in the entire database. In versions
of the database since the introduction of Oracle9i, youstill set a default block size for
the database, but you can also have up to five other block sizes in a database (though
only a single block size for each tablespace). Figure 2-4 illustrates the relationship of
Oracle blocks to operating system blocks.
Datafiles belong to only one database and to only one tablespace within that database.


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