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Lesson 3Duplex and multiple archive logs
ObjectiveImplement duplex or multiple archive logs.

Duplex and Multiple Archive Logs

Oracle enables the (ARCH) background archive process, or its foreground equivalent, to archive online redo log files to multiple destinations. Up to five destinations can be specified with the initialization parameter:
LOG_ARCHIVE_DEST_n. This parameter defines a destination and attributes for the archive redo log file group. The parameter number suffix is defined as the handle[1] displayed by the fixed-table queries. The destination can be a local disk-based file, or it can be a user-specified standby database that is either local or remote to the primary database. It has been observed that two archival destinations are not enough, though five or more is excessive and provides no additional benefit.

In the following code, you can see an example of usage of the parameter, where the first location of the archived redo log file is within the local hard disk.
LOG_ARCHIVE_DEST_1 = "LOCATION=D:\ORACLE\ORADATA\STBY\ARCHIVE"

A maximum of five destinations may be specified. The first destination specified is treated as the primary destination. The remaining destinations are secondary. At least one archive destination must be a local disk. One archive destination is MANDATORY, although none may actually be specified. If no destinations are specified, the appropriate initialization parameters are used as defaults.

LOG_ARCHIVE_DUPLEX_DEST

is similar to
LOG_ARCHIVE_DEST

This parameter introduced within Oracle8 is deprecated[2] within Oracle8i. LOG_ARCHIVE_DEST_n must be used instead within Oracle8i and later.
This parameter specifies a second (duplex) archive destination. If LOG_ARCHIVE_DUPLEX_DEST is set to a NULL string ("") or (`'), it means that there is no duplex archive destination. The default of this parameter is a NULL string.
In the following simulation, we will set the parameter value of LOG_ARCHIVE_DUPLEX_DEST and LOG_ARCHIVE_DEST_n using the ALTER SYSTEM command within SQL*Plus. Because these two parameters are dynamic, they can be changed using SQL*Plus.

Setting Parameter-values

The following MouseOver illustrates the syntax and provides an example for the LOG_ARCHIVE_DUPLEX_DEST and LOG_ARCHIVE_DEST_n initialization parameters.

  1. The name of the initialization parameter, this is used to set multiple destinations for archived redo log files
  2. This is the value set to the parameter. The value in the form of a character string must be a directory name for saving the duplexes of archived redo log files.
  3. The name of the parameter, which is used to define multiple locations for archived redo log files, where n, is an integer between 1 and 5.
  4. The value of the parameter can be set to a NULL string.
  5. SERVICE specifies the destination of a standby database, which will be used to transmit the archivelog. There must be a standby instance associated with the destination
  6. LOCATION specifies a local file-system.
  7. MANDATORY specifies that archiving to the destination must succeed before the REDO log file can be made available for re-use.
  8. OPTIONAL specifies that successful archiving to the destination is not required before the REDO log file can be made available for re-use
  9. REOPEN specifies an interval of time (in seconds) that must pass after an error is encountered during archiving to the destination before future archives to the destination can be attempted.

Archive Log Parameters

LOG_ARCHIVE_DUPLEX_DEST

LOG_ARCHIVE_DUPLEX_DEST is similar to the initialization parameter LOG_ARCHIVE_DEST. This parameter specifies a second archive destination: the duplex archive destination. This duplex archive destination can be either a must-succeed or a best-effort archive destination, depending on how many archive destinations must succeed (as specified in the LOG_ARCHIVE_MIN_SUCCEED_DEST parameter). The default setting of a null string ("") or (' ') indicates that a duplex archive destination does not exist.

Property Description
Parameter type String
Syntax LOG_ARCHIVE_DUPLEX_DEST = filespec
Default value There is no default value.
Modifiable ALTER SYSTEM
Range of values Either a null string or any valid path or device name, except raw partitions
Basic No

Note: If you are using Oracle Enterprise Edition, this parameter is deprecated in favor of the LOG_ARCHIVE_DEST_n parameters. If Oracle Enterprise Edition is not installed or it is installed but you have not specified any LOG_ARCHIVE_DEST_n parameters, this parameter is valid. The next lesson demonstrates how to detect and repair corrupted blocks.

[1]Handle: A handle is a connection to the database server, which completes a transaction for the user.
[2]Deprecated: When a certain feature or functionality is no longer advisable for use or will no longer be supported on the Oracle database server, that feature is called deprecated.