> (you don't have to strictly follow this form)

**Use case**

Sometimes, for really sophisticated scenarios it can be hard to control the amount of in-progress backups run externally. For the purpose of simpler control we can introduce server-level setting which disallows running concurrent backups of any type. 

Something like this in `config.xml` (enabled by default):
`<allow_concurrent_backups>true</allow_concurrent_backups>`

**Describe the solution you'd like**

It's important that backups can be executed in distributed way on multiple servers. Need to take it into account.

**Describe alternatives you've considered**
External check of `system.backups` table, but it can be complex.

: Poco::UUID(bytes, version) {}
        };
        query_id_to_set = QueryUUID(random.bytes, Poco::UUID::UUID_RANDOM).toString();
    }
    client_info.current_query_id = query_id_to_set;
    if (client_info.query_kind == ClientInfo::QueryKind::INITIAL_QUERY)
        client_info.initial_query_id = client_info.current_query_id;
}
void Context::killCurrentQuery() const