ZBX-6118 fix, there is an issue with updating an item on template, linked to many hosts.
Here is a very slow query in item.update method (new approach implemented in the
ZBX-6118, code comment //Check if item with a new key already exists on the child host.):
and possible related issue:
~13000 hosts are linked to the template.
There is an opinion from dotneft that, quote: During item update in a template "itemid" order is not ascending. Which lead to possible deadlock, especially with log items.
It's decided to fix it separately of ZBX-3783 because its critical.