I tried changing priority of DCP connection as follows:
1. Set priority when DCP connection was set up. – no error here.
2. Set/change priority after DCP connection was set up.
The following error was seen in memcached log at step 2.
2018-12-04T10:55:00.239768Z WARNING 512096080: cookie_get_priority: priority (which is 16) is not a valid CONN_PRIORITY - closing connection (<86>^^A@@@@<86>^^A@@@à<86>^^A@@@<80>,<86>^^A@@@Ð-<86>^^A@@@@/<86>^^A@@@p
I tried setting different priorities at step 1 and step 2, and the same error message about invalid value of 16 was returned regardless. There seems to be issues with the way the dcp connection maintains priority.