Information about the database is stored in different sections of the
control file. Each section is a set of records about an aspect of the database.
For example, one section in the control file tracks data files and contains a
set of records, one for each data file. Each section is stored in multiple
logical control file blocks. Records can span blocks within a section.
The control file contains the following types of records:
These records contain noncritical information that is eligible to be
overwritten if needed. When all available record slots are full, the database
either expands the control file to make room for a new record or overwrites the
oldest record. Examples include records about:
LOG HISTORY
OFFLINE RANGE
ARCHIVED LOG
BACKUP SET
BACKUP PIECE
BACKUP DATAFILE
BACKUP REDOLOG
DATAFILE COPY
BACKUP CORRUPTION
COPY CORRUPTION
DELETED OBJECT
PROXY COPY
These records contain critical information that does not change often
and cannot be overwritten. Examples of information include tablespaces, data
files, online redo log files, and redo threads. Oracle Database never reuses
these records unless the corresponding object is dropped from the tablespace.
Examples of non-circular controlfile sections (the ones that can only expand)
DATABASE (info)
CKPT PROGRESS (Checkpoint progress)
REDO THREAD, REDO LOG (Logfile)
DATAFILE (Database File)
FILENAME (Datafile Name)
TABLESPACE
TEMPORARY FILENAME
RMAN CONFIGURATION
Reading and writing the control file blocks is different from reading
and writing data blocks. For the control file, Oracle Database reads and writes
directly from the disk to the program global area (PGA). Each process allocates
a certain amount of its PGA memory for control file blocks.
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V$CONTROLFILE
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Lists the names of control files
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V$CONTROLFILE_RECORD_SECTION
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Displays information about control file record sections
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