'kill <query id>' gives ERROR 1095 (HY000): You are not owner of thread … even though I am

Question

I did an ALTER TABLE on a huge table on a MariaDB Galera Cluster 10.2, but after a while of waiting I changed my mind and tried to kill the connection. However, MariaDB said ERROR 1095 (HY000): You are not owner of thread 123 even though I most definitely am the owner. So what is going on?

Answer 1

The error message is misleading. Galera can mark user threads as high priority which means they can't be killed. Currently, this gives the ERROR 1095 (HY000): You are not owner of thread... See MDEV-12008 for details.

This will probably affect other distributions of Galera as well, such as Percona XtraDB Cluster.