The db-control online-backup uses pg_dump to make a online backup of the spacewalk/satellite database. The pg_dump utility has the ability to compress the data base dump and it would be useful to have the ability to compress the backup on the fly to reduce overall disk usage of the backups as they can get rather large.
The pg_dump is called with -Fc -Z7 since Spacewalk 1.8 so it is compressed as much as possible. What output do you experience?
running "db-contol online-backup /var/lib/pgsql/backup/rhsat-20140106" just gives me a file that I can view and see all the raw sql statements where I would be expecting gzip data and if I do "file /var/lib/pgsql/backup/rhsat-20140106" it reports it as "PostgreSQL custom database dump - v1.11-0" where I would expect it to be likely reporting a gzip archive.
Spacewalk project as an upstream for Red Hat Satellite 5 product is going to be End Of Life on May 31 2020. Spacewalk 2.10 has been released as the last release of this project. https://github.com/spacewalkproject/spacewalk/wiki/ReleaseNotes210 Any new feature will not be included therefore closing remaining RFEs to set expectations properly.