Oracle7 Server Administrator's Guide

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Tuning Archiving

This section describes aspects of tuning the archive process, and includes the following topics:

For most databases, the archive process has no effect on overall system performance. In some large database sites, however, archiving can have an impact on system performance. On one hand, if the archiver works very quickly, overall system performance can be reduced while the archiver runs, since CPU cycles are being consumed in archiving. On the other hand, if the archiver runs extremely slowly, it has little detrimental effect on system performance, but it takes longer to archive redo log files, and can be a bottleneck if all redo log groups are unavailable because they are waiting to be archived.

For these large database sites, you can tune archiving, to cause it to run either as slowly as possible without being a bottleneck, or as quickly as possible without reducing system performance substantially. To do so, adjust the values of the initialization parameters LOG_ARCHIVE_BUFFERS (the number of buffers allocated to archiving) and LOG_ARCHIVE_BUFFER_SIZE (the size of each such buffer).

Note: When you change the value of LOG_ARCHIVE_BUFFERS or LOG_ARCHIVE_BUFFER_SIZE, the new value takes effect the next time you start the instance.

Minimizing the Impact on System Performance

To make the archiver work as slowly as possible without forcing the system to wait for redo logs, begin by setting the number of archive buffers (LOG_ARCHIVE_BUFFERS) to 1 and the size of each buffer (LOG_ARCHIVE_BUFFER_SIZE) to the maximum possible.

If the performance of the system drops significantly while the archiver is working, make the value of LOG_ARCHIVE_BUFFER_SIZE lower, until system performance is no longer reduced when the archiver runs.

Note: If you want to set archiving to be very slow, but find that Oracle frequently has to wait for redo log files to be archived before they can be reused, consider creating additional redo log file groups. Adding groups can ensure that a group is always available for Oracle to use.

Improving Archiving Speed

To improve archiving performance (for example, if you want to stream input to a tape drive), use multiple archive buffers, so that the archiver process can read the archive log at the same time that it writes the output log. You can set LOG_ARCHIVE_BUFFERS to 2, but for a very fast tape drive you might want to set it to 3 or more. Then, set the size of the archive buffers to a moderate number, and increase it until archiving is as fast as you want it to be without impairing system performance.

See Also: This maximum is operating system dependent; see your operating system-specific Oracle documentation.

For more information about these parameters, see the Oracle7 Server Reference guide.


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