Archive Log Compression Options and Reducing Network Traffic

[Mike Donovan]

By default Dbvisit will zip the archive logs before transferring to the DR site, and Dbvisit uses industry proven compression methods to compress the archive logs. The specific compression method that Dbvisit uses depends on the compression method installed on your server. So this can be compress or gzip, etc. The Dbvisit internal compression method uses the zlib compression method, and this will be used on Windows.

It is very difficult to give a percentage estimate as to how much an archive log file will be compressed, as this really depends on the data contained within the archive log file. So each archive log file may be compressed differently in terms of percentages.

Here is an example. These are 2 archive log files from the same database:

(Archive log file 1)
-rw-r----- 1 oracle dba 27136 Nov 1 15:53 arch_1_1776.log (uncompressed)
-rw-r----- 1 oracle dba 7889 Nov 3 08:27 arch_1_1776.log.gz (compressed)

(Archive log file 2)
-rw-r----- 1 oracle dba 75776 Nov 3 08:27 arch_1_1782.log (uncompressed)
-rw-r----- 1 oracle dba 13778 Nov 1 17:09 arch_1_1782.log.gz (compressed)

Archive log file 1 is compressed:
(1-(7889/27136))*100= 70%

and archive log 2 is compressed:
(1-(13778/75776))*100 = 81%

Our experience tells us that it is normal to get between 70%-80% compression, sometimes more. This means that you will get a 70%-80% reduction in network traffic. To determine the level of compression you are likely to get simply try compressing some of your archive log files using compress or gzip and compare the size of the compressed file with the original.

Dbvisit uses ssh (secure shell) for transferring (shipping) the archive log to the DR site. With Dbvisit it is also possible to use ssh compression. In this case, the archive log does not have to be compressed before transfer as the archive log is compressed on the fly with ssh.

During Dbvisit testing the different compression methods can be tested to determine which method works best for your site.

[Mike Donovan]

By default Dbvisit uses zlib compression.
You can manually compress a file with the following command:
dbv_functions –g

To uncompress:
dbv_functions –u

[Mike Donovan]

COMPRESS=ssh: This means that the logs are compressed on the fly and will not be left compressed on the server. However, for longer distance, slower networks, it is more efficient to set:
COMPRESS = dbvisit (and UNCOMPRESS=dbvisit)

This will compress the logs first and then transfer them. They will be left compressed on the server. If you want to leave them uncompressed on the server then set LEAVE_COMPRESS_SOURCE=No

[Mike Donovan]

Another feature included in Dbvisit is the ability to limit the actual amount of bandwidth used. This is an option set in the DDC variable CP_OPTIONS, where you specify limits for the bandwidth used in Kbit/s.

CP_OPTIONS:
Allow for different secure copy (scp) options.
For example (Unix/Linux):
-l limit

Limits the used bandwidth, specified in Kbit/s
See man scp in Unix and Linux for scp options.
See sftpc on Windows for scp options.

Sample:
CP_OPTIONS=-l 100