Specifying the Archived Redo Log Filename Format and Destination

Archived redo log files are uniquely named as specified by the LOG_ARCHIVE_FORMAT parameter. Filename format is operating system specific; for most operating systems it consists of a text string, one or more parameters, and a filename extension. When a filled online redo log group is archived, the archiving process concatenates the supplied text string with the return values of the specified parameters to create uniquely identified archived redo log files. Each parameter has an upper bound, which is operating system dependent.

Table 22 - 1 lists the parameters that can be included in a filename format and corresponding examples to show how the parameter affects the filenames created by the archiving process.

Parameter	Description	Example1
%T	thread number, left-zero-padded	arch0000000001
%t	thread number, not padded	arch1
%S	log sequence number, left-zero-padded	arch0000000251
%s	log sequence number, not padded	arch251
Table 22 - 1. Archived Redo Log Filename Format Parameters

¹ Assume LOG_ARCHIVE_FORMAT=arch%parameter, and the upper bound for all parameters is 10 characters.

The different options are provided so that you can customize the archived redo log filenames as you need. For example, you might want to take into account the operating system sorting algorithm used to list filenames.

The %T and %t are useful only when the Oracle Parallel Server is used. In a non-Parallel Server configuration, you must decide whether to use %S or %s to identify each archived redo log file uniquely. The following is a typical example of a common archived redo log filename format:

LOG_ARCHIVE_FORMAT = arch%S.arc

Here, arch is the filename, %S is the zero-padded log sequence parameter, and .arc is the file extension. Assuming the upper bound for the %S parameter is four, this filename format generates archived redo log filenames of the following format:

arch0001.arc

arch0002.arc

arch0003.arc

 .

 .

Take into account the maximum operating system filename length when specifying the archive filename format. If ARCH or a user process attempts to archive a file and the supplied filename format is too large, the process fails to archive the file.

Note: If no archived filename format is specified using LOG_- ARCHIVE_FORMAT, Oracle uses a default filename format that is operating system-specific.

The archived redo log destination is also operating system-specific. For most operating systems, the archive redo log destination points to a disk drive and a file directory. If permitted by your Oracle Server, this destination can also point to a tape drive dedicated to Oracle for archiving filled online redo log files.

The archived redo log destination is determined at instance startup by the LOG_ARCHIVE_DEST initialization parameter, but can be overridden while the instance is up:

• If a database's parameter file is edited to include a destination using the LOG_ARCHIVE_DEST parameter, the current instance must be shut down and restarted to read the new parameter file.

• If the current instance cannot be shut down, but the archived redo log destination must be specified or changed for automatic archiving, use the ALTER SYSTEM ARCHIVE LOG START 'destination' statement to override the automatic archiving destination.

• During manual archiving, a specified destination overrides the default archived redo log destination. However, automatic archiving continues to use the current automatic archive destination. If no destination is specified, Oracle automatically uses the destination specified by the LOG_ARCHIVE_DEST parameter of the parameter file used to start the instance. If no destination is supplied by the LOG_ARCHIVE_DEST parameter, Oracle uses a default destination that is operating system-dependent.

For more information about filename format parameters and the term "thread" see the Oracle7 Parallel Server Concepts & Administration guide.