Copyright © 2019 MariaDB. All rights reserved.
It seems that under some use cases enabling compression won't actually reduce the log size, because only selected events are compressed inside the log and this compression will not include COMMIT events, item names nor query plaintext produced by binlog_annotate_row_events which is ON, by default in mariadb 10.2
So you may have wrong impression that something is not working as expected, because log size will stay the same, but in fact everything is ok, just your db traffic may not always be"compressible" using this approach...
thank you SO MUCH for pointing this out! The row annotations were easily doubling the size of my binlogs.