A performance issue during access to multiple database elements

[mkraposhin]

When requesting information about many (> 5000) elements (virtual machine interfaces, virtual networks, etc) via VNC config client, it might create long delays (due to querying Config or Cassandra DB) which might create timeout errors.

The situation happens, for instance, in Web UI for requests of 5000 VNs : /virtual-networks?detail=true&fields=physical_router_back_refs,floating_ip_pools,bridge_domains

The similar case can be also reproduced using request of information for 5000 ports (virtual machine interfaces)

[aignatov]

some performance improvement might be achieved with this patch: https://gerrit.opensdn.io/c/opensdn-io/tf-controller/+/826