Databases Reference
In-Depth Information
The major background processes include
•
DBWn: The database writer writes blocks from the database buffer cache to the data files.
•
CKPT: The checkpoint process writes checkpoint information to the control files and
data file headers.
•
LGWR: The log writer writes redo information from the log buffer to the online redo logs.
•
ARCn: The archiver copies the content of online redo logs to archive redo log files.
•
RVWR: The recovery writer maintains before images of blocks in the fast recovery area.
•
MMON: The manageability monitor process gathers automatic workload repository statistics.
•
MMNL: The manageability monitor lite process writes statistics from the active session history
buffer to disk.
•
SMON: The system monitor performs system level clean-up operations, including
instance recovery in the event of a failed instance, coalescing free space, and cleaning up
temporary space.
•
PMON: The process monitor cleans up abnormally terminated database connections and also
automatically registers a database instance with the listener process.
•
RECO: The recoverer process automatically resolves failed distributed transactions.
The structure of the SGA varies by Oracle release. You can view details for each component via this query:
SQL> select pool, name from v$sgastat;
The major SGA memory structures include
•
SGA: The SGA is the main read/write memory area and is composed of several buffers, such as
the database buffer cache, redo log buffer, shared pool, large pool, java pool, and streams pool.
•
Database buffer cache: The buffer cache stores copies of blocks read from data files.
•
Log buffer: The log buffer stores changes to modified data blocks.
•
Shared pool: The shared pool contains library cache information regarding recently executed
SQL and PL/SQL code. The shared pool also houses the data dictionary cache, which contains
structural information about the database, objects, and users.
Finally, the program global area (PGA) is a memory area separate from the SGA. The PGA is a process-specific
memory area that contains session-variable information.
Summary
After you've installed the Oracle binaries, you can create a database. Before creating a database, make sure you've
correctly set the required OS variables. You also need an initialization file and to pre-create any necessary directories.
You should carefully think about which initialization parameters should be set to a nondefault value. In general, I try
to use as many default values as possible and only change an initialization parameter when there is a good reason.
This chapter focused on using SQL*Plus to create databases. This is an efficient and repeatable method for
creating a database. When you're crafting a
CREATE DATABASE
statement, consider the size of the data files and online
redo logs. You should also put some thought into how many groups of online redo logs you require and how many
members per group.
