Summary: Running too large of a select causes primproc to disappear, seems linked to ram usage and running out.
The work around is to add "-q" flag to the mariadb client so that the results from columnstore are not fully buffered in mariadbd before returning to the client. But this work around is unacceptable for 3rd party integrations and simplified user experience

Expectation: Columnstore software stays stable. Rejecting or erroring out too large of queries, self recovery or maybe an error message suggesting what is needed to complete the query (cpu/ram) but a subprocess disappearing and system staying broken until manual intervention to restart the system isn't acceptable.

Workaround: restart columnstore

Reproduction: See developer comment

Client Side error:

ERROR 1815 (HY000) at line 1: Internal error: MCS-2004: Cannot connect to ExeMgr.

primproc.log

getFreeMemory : returned from  getMemUsageFromCGroup : usage 5211672576 (GIB) 4

debug.log

Oct  6 17:29:47 mcs1 messagequeue[794]: 47.156748 |0|0|0| W 31 CAL0071: InetStreamSocket::read: timeout during first read: socket read error: Success; InetStreamSocket: sd: 65 inet: 127.0.0.1 port: 8601; Will retry.

mariadb-error.log

ClientRotator caught exception: InetStreamSocket::connect: connect() error: Connection refused to: InetStreamSocket: sd: 64 inet: 127.0.0.1 port: 8601