about the server group GET API

Hello experts, I have a question about the server group GET rest API. I tried out the GET API and found it was pretty slow (around 200 servers returned in 8 seconds). By skimming through the codebase I am suspecting filtering out group members is heavy ( https://github.com/openstack/nova/blob/4100d4d8fbaa6416ea37d8cb3e64003f40ee1... ). So my question is do we clear out the instance_group_member table after deleting instances? If not, why could we not do it? Thank you very much for help. . -- Best Regards, Jiatong Shen