I've been trying to make use of the compressed replication protocol between two existing MariaDB 10.1.21 boxes.  Replication itself has been working fine for a while.

I do:

SET GLOBAL slave_compressed_protocol = 1;

On both master and slave.  Then stop/start slave.

However, when I monitor the network usage, I see no reduction in network traffic.  However, I tried compression via an ssh tunnel and saw a big reduction (ssh doing the compression, not MariaDB).  So the traffic is definitely compressible.

I tried setting the param via my.cnf and also restarting both master and slave to see if that would make a difference - no luck.  Have confirmed the global variable shows 'ON' after the change, and was 'OFF' before.

Is there potentially an issue with this working with the MariaDB supplied binary tarball (e.g. some compression lib dependency?)  I see nothing in error.log to show an issue.  Any other useful ways to debug this?

Thanks!

Phil