SAP PI 7.3 dual stack: SMQ2 issue - flooded with IDocs

Dear experts,

A few days ago we had an issue where on of our SAP ERP systems "flooded" SAP PI 7.3 with > 1 million MATMAS IDocs over night. This was obviously a mistake on SAP ERP side.
SAP PI kept working but the SMQ2 (Inbound Queue) had 220 000 entries in the morning. We were not able to delete queues because also other business relevant messages were included in them.

We could have manually opened each queue and each entry and then manually deleted message by message. With 220 000 messages this is useless. We just waited for a long time until the queue was completetly processed.

Has anyone of you had an expierience like that? How could such a situation be solved or be avoided in the first place? I am now looking into setting up "Queue Prioritization" for MATMAS IDocs.

Thank you for any comments or best-practices in such a case.

Best regards, Peter