some files already gzipped causes rsync to not compress any?

[Steven Roberts]

Greetings,
We have encountered an odd performance issue in rsync (running version 2.4.6).

We have an rsync server set up in our production environment (at a colo
facility).  A backup machine in our office (which is connected to the colo by a
3Mbit pipe) is doing a rsync -a -v -z --delete on a directory.  If the first
few files in the directory are already gzip'd then we don't get any increase in
the transfer rate once we get to the non compressed files.  If none of the
files in the directory are already compressed we get the expected compression
of the data.

The data in question is Oracle rman files that typically get 2.5x compression.

We have worked around this by either compressing all of them or none of
them in the soruce directory.  But this behavior seems odd.

I looked through the changelogs between my version and current but didn't see anything.
If it is fixed in a newer version, please let me know (and if it is in the
changelog, I apologize in advance).

Please let me know what additional information is needed (if any) or if
you need me to run tests.

Regards,
Steven Roberts