What happens to a waiting WebSocket connection on a TCP level when server is busy (blocked)

I am load testing my WebSocket Tornado server, running on Ubuntu Server 14.04.

I am playing with a big client machine loading 60,000 users, 150 a second (that's what my small server can comfortably take). Client is a RedHat machine. When a load test suite finishes, I have to wait a few seconds to be able to rerun.

Within these few seconds, my websocket server is handling closing of the 60,000 connections. I can see it in my graphite dashboard (the server logs every connect and and disconnect information there).

I am also logging relevant outputs of the netstat -s and ss -s commands to my graphite dashboard. When the test suite finishes, I can immediately see tcp established seconds dropping from 60,000 to ~0. Other socket states (closed, timewait, synrecv, orphaned) remain constant, very low. My client's sockets go to timewait for a short period and then this number goes to 0 too. When I immediately rerun the suite, and all the tcp sockets on both ends are free, but the server has not finished processing of the previous closing batch yet, I see no changes on the tcp socket level until the server is finished processing and starts accepting new connections again.

My question is - where is the information about the sockets waiting to be established stored (RedHat and Ubuntu)? No counter/queue length that I am tracking shows this.

Thanks in advance.