Comments - Parallel Replication
Content reproduced on this site is the property of its respective owners,
and this content is not reviewed in advance by MariaDB. The views, information and opinions
expressed by this content do not necessarily represent those of MariaDB or any other party.
Note that Parallel Replication is about how a replication slave applies updates received from the master. SELECT statements do not modify the database and thus are never replicated. So Parallel Replication has no relevance to SELECT statements.
I do not know if tokudb has optimisations for running a single SELECT in parallel. The server layer of mariadb does not.