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Oracle DBA Pocket Guide
cached, again using an LRU algorithm. The shared pool is
also used for caching information from the Oracle data dictio-
nary, which is the metadata that describes the structure and
content of the database itself.
Redo log buffer
The redo log buffer caches redo information in order to
improve performance. Oracle caches the information until it
can be written to the redo log on disk at a more optimal time,
which avoids the overhead of constantly writing to disk.
Large pool
The large pool is an optional area of the SGA used for buffer-
ing I/O for various server processes, including those used for
backup and recovery. The area is also used to store session
memory for the Shared Server (formerly known as the Multi-
Threaded Server, or MTS) and when using the XA protocol
for distributed transactions.
Files
Four types of files are used by the Oracle instance: control
files, datafiles, redo log files, and parameter files. When you
START the instance, the parameter file is read. When you
MOUNT the database, the control files are read. When you
OPEN the database, the datafiles and redo log files are refer-
enced. When a database is being updated, changes are
recorded in the online redo log files, which provide a mecha-
nism for recovery in case of a failure.
Parameter files
These files (either the INIT.ORA file or the SPFILE) specify
how the instance is configured and point to the control ...