Configuring file creation in Flash recovery area and order of Precedence (文档 ID 305810.1)
***Checked for relevance on 9-Sep-2013***
PURPOSE
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Configuring file creation in Flash Recovery Area and order of
precedence for these Files
SCOPE & APPLICATION
-------------------
New Feature in Oracle10G and for DBAs, support
Configuring Online RedoLog Creation in the Flash Recovery Area
================================================================
The following statements can create online redologs in the Flash
Recovery Area:
- CREATE DATABASE
- ALTER DATABASE ADD LOGFILE
- ALTER DATABASE ADD STANDBY LOGFILE
- ALTER DATABASE OPEN RESETLOGS
The default size of an online redolog created in the Flash Recovery Area is 100 MB.
The log member filenames are automatically generated by the database.
The initialization parameters that determine where online redolog files are
created are DB_CREATE_ONLINE_LOG_DEST_n, DB_RECOVERY_FILE_DEST and
DB_CREATE_FILE_DEST.
Order of Precedence for Online Redo Log Creation
====================================================
o If DB_CREATE_ONLINE_LOG_DEST_n is specified, an online redolog file member is
created in each directory up to MAXLOGMEMBERS for the database. No online
redologs are created in the Flash Recovery Area .
o If the DB_CREATE_FILE_DEST and DB_RECOVERY_FILE_DEST parameters are specified,
and if the DB_CREATE_ONLINE_LOG_DEST_n parameter is not specified, an online
redolog file member is created in both DB_CREATE_FILE_DEST and
DB_RECOVERY_FILE_DEST up to MAXLOGMEMBERS. The file in DB_CREATE_FILE_DEST is
the first member.
o If DB_RECOVERY_FILE_DEST is specified and DB_CREATE_FILE_DEST or
DB_CREATE_ONLINE_LOG_DEST_n are not specified, an online redolog file member is
created in DB_RECOVERY_FILE_DEST.
o If DB_CREATE_ONLINE_LOG_DEST_n, DB_CREATE_FILE_DEST, or
DB_RECOVERY_FILE_DEST are all not specified, an online redo log file is
created in an operating system' specific default location (eq $ORACLE_HOME/dbs).
The file is not created as an Oracle Manager File (OMF).
Configuring Control File Creation in the Flash Recovery Area
==============================================================
The initialization parameters CONTROL_FILES, DB_CREATE_ONLINE_LOG_DEST_n,
DB_RECOVERY_FILE_DEST, and DB_CREATE_FILE_DEST all interact to determine the
location where the database control files are created
If the database creates an Oracle managed control file, and if the database
uses a server parameter file (SPFILE), then the database changes the CONTROL_FILES
initialization parameter in the server parameter file (SPFILE). If the database uses a
client-side initialization parameter file (PFILE), then change the CONTROL_FILES
initialization parameter manually in the client-side parameter file (PFILE) after the
contolfiles have been created.
Order of Precedence for Control File Creation
===============================================
o If DB_CREATE_ONLINE_LOG_DEST_n is specified, an OMF control file is
created in each directory. The file in the first directory is the
primary control file. No control file is created in the Flash Recovery Area .
o If DB_CREATE_FILE_DEST and DB_RECOVERY_FILE_DEST are specified, and if
DB_CREATE_ONLINE_LOG_DEST_n is not specified, an OMF control file is created
in both DB_CREATE_FILE_DEST and DB_RECOVERY_FILE_DEST. The file in the
DB_CREATE_FILE_DEST is the primary control file.
o If DB_RECOVERY_FILE_DEST is specified and DB_CREATE_ONLINE_LOG_DEST_n or
DB_CREATE_FILE_DEST are not specified, an OMF control file is created in
DB_RECOVERY_FILE_DEST.
o If DB_CREATE_ONLINE_LOG_DEST_n, DB_CREATE_FILE_DEST, and
DB_RECOVERY_FILE_DEST are not specified, a control file is created in an
operating system' specific default location. This control files are not
in OMF format.
Archived Redo Log Creation in the Flash Recovery Area
======================================================
It is recommended that you the use Flash Recovery Area as an archivedlog
location because the archived logs are automatically managed by the database.
Whatever archiving scheme you choose, it is always advisable to create multiple
copies of archived logs.
The following basic options are available, listed from most to least recommended:
1. Enable archiving to the Flash Recovery Area and set other LOG_ARCHIVE_DEST_n
initialization parameter to locations outside the Flash Recovery Area .
2. Enable archiving to the Flash Recovery Area only and use disk mirroring to
create copies of the archived redo logs.
3. Set LOG_ARCHIVE_DEST_n initialization parameters to archive only to
none-Flash Recovery Area locations.
Using the Flash Recovery Area, ommits the use of LOG_ARCHIVE_DEST
and LOG_ARCHIVE_DUPLEX_DEST initialization parameters. Use the
LOG_ARCHIVE_DEST_n parameters instead, which have somewhat different semantics.
Once a database is using LOG_ARCHIVE_DEST_n, it can configure a Flash
Recovery Area.
Order of Precedence for Archive log file Creation
====================================================
The interactions among different initialization parameters affecting redo
log archiving desintations are as follows:
o If LOG_ARCHIVE_DEST (and, optionally, LOG_ARCHIVE_DUPLEX_DEST) is set, these
parameters will specify the only redolog archiving destinations.
o If DB_RECOVERY_FILE_DEST is specified (that is, if a Flash Recovery Area is
configured) and no LOG_ARCHIVE_DEST_n is specified, then LOG_ARCHIVE_DEST_10
is implicitly set to the Flash Recovery Area.
This behaviour can be overrulled by explicitly setting
LOG_ARCHIVE_DEST_10 to an empty string.
o If you set any local destinations for LOG_ARCHIVE_DEST_n, then archived redo
logs are stored only in the specified destinations.
In this case, redolog files are not archived in the Flash Recovery Area by
default.
Changes in SQL Statement Behavior
===================================
- ALTER DATABASE
o ADD LOGFILE and ADD STANDBY LOGFILE: If a file name is not provided and if
the initialization parameter DB_CREATE_ONLINE_LOG_DEST_n has not been defined,
then an online redolog file member is created in the Flash Recovery Area .
o DROP LOGFILE: OMF online redolog file members in the Flash Recovery Area
are deleted.
o RENAME FILE: The old filename can be an OMF Flash Recovery Area filename.
If the file exists, it is deleted.
- CREATE CONTROLFILE
The control file is created in the file specified by the CONTROL_FILES
initialization parameter or in the default control file destination according
to the order of precedence.
- CREATE DATABASE
If CONTROL_FILES is not set and at least one of DB_CREATE_FILE_DEST,
DB_CREATE_ONLINE_LOG_DEST_n, and DB_RECOVERY_FILE_DEST is set, then
the control file is created in the default destination following the order of
precedence. If the LOGFILE clause is omitted and at least one of
DB_CREATE_FILE_DEST, DB_RECOVERY_FILE_DEST, and DB_CREATE_ONLINE_LOG_DEST_n is
set, the members are created in the default destination
Note :-
If both db_create_online_log_dest_n and db_recovery_file_dest are specified in
the init parameters and both have same destination, it could cause the
following warning message to be logged in the alert log:
WARNING: db_create_online_log_dest_2 is same as db_recovery_file_dest
REFERENCE
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Note 305817.1 FAQ - Flash Recovery Area feature of 10G
- Oracle Database Products > Oracle Database > Oracle Database > Oracle Database - Enterprise Edition > Recovery Manager