Few Oracle DB Terms

Alert log
---------
In BACKGROUND_DUMP_DEST - Name: alert.log

Archived redo logs
--------------------
In ARCHIVELOG mode, generated when Oracle switches online redo logs - LGWR process
Can be up tp 10 destinations - LOG_ARCHIVE_DEST_n

Backup control file
-------------------
Generated by:
alter database backup controlfile to 'file_name';
or
alter database backup controlfile to trace;

Checkpoint
-------------
DB event that causes dirty buffers from memory to be written to disk.

DB Parameter file
-------------------
Has DB and instance configuration information.
spfile.ora - Binary file altered using alter system command
init.ora - text file

Flash Recovery Area
-----------------------
Optional area to store recovery related files like
RMAN backups,
archived redo logs,
online redo logs,
control files

Instance
---------
A unique set of Oracle Processes and memory from a machine that manipulates a given database (db files, control files, online redo log files, archived redo log files, Flashback logs).
An instance is associated with only one database at a given time.

The basic processes that make up an instance are:
PMON
SMON
DBWn
LGWR
CKPT

The basic RAM memory that are associated with an instance are:

SGA(System Global Area - SGA_TARGET and SGA_MAX_SIZE):

DB buffer cache - DB_CACHE_SIZE and DB_nk_CACHE_SIZE
Shared pool - SHARED_POOL_SIZE
Redo log buffer - LOG_BUFFER
Large pool - LARGE_POOL_SIZE
Java pool - JAVA_POOL_SIZE
Streams pool - STREAMS_POOL_SIZ

PGA(Program Global Area - PGA_AGGREGATE_TARGET):

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Online redo logs
------------------
Min - 2 online redo logs
log switch occurs when the current redo log file fills up or can be forced (by a DBA/privileged user) using SQL>alter system switch logfile; .
Each online redo log has a unique log sequence number - This is also associated with its
corresponding Archived redo log file.
Log sequence number of a log file is entered in V$LOG view.
Log sequence number associated with an Archived Redo log is entered in V$ARCHIVED_LOG view.

An online Redo log has a range of DB System Change Numbers (SCNs).

System Change Number (SCN)
--------------------------------
A number (a counter) to represent the state of a DB at a given point in time.

Trace files
------------
Files that has the list of commands/operations executed by the DB or a process or a session or a program etc that can be used for debugging purposes.

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-Suresh