During some testing in MDEV-32984 (with some create table examples that are relevant here), I noticed that the query will hang for a long time if you create the tables and then power off the server with the InnoDB base table:

• create the federatedx table
• turn off the server with the innodb table
• issue a select *
• restart mariadb takes around two minutes

If, instead of restart, you try first to "kill" the select in processlist, it switches from Query to Killed but hangs around in state Statistics for the full two minutes. I couldn't find a way to configure a timeout but perhaps the engine could kill the query more quickly, if it hasn't made a connection yet, and there is no need to eg rollback?