Steps to reproduce:

1. Create "Template host discovery" with lld rule and 1 host prototype.
2. Create "Template port discovery" with lld rule and 16 item prototypes (each using LLD macro {#PORT}), 4 trigger prototypes, 2 graph prototypes.
3. Discover 300 hosts, link "Template port discovery" to each.
4. For each discovered host discover 1 to 4 ports, randomly.
5. When everything is discovered, go to frontend and delete host prototype from "Template host discovery".

Result:
Huge SQL query is generated and it cannot be processed by server giving error "MySQL has gone away". I could not copy-paste the "details" from frontend, it was too huge but the page source file was 9 MB.

Expected:
All data deleted, by splitting huge SQL into parts.

Note
In order to delete all the discovered data I had to feed the host discovery rule an empty JSON. The server handled the task with no problems.