I thought it would be interesting to see some performance testing. This time we simulate 1000 request with 5 concurent connections.

[demo]# ab -c 5 -n 1000 http://demo.livehelperchat.com/index.php/chat/syncuser/6/22/1e16f65d63f270401f90082a6fac9f3200ddab5d
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking demo.livehelperchat.com (be patient)
Completed 100 requests
Completed 200 requests
Completed 300 requests
Completed 400 requests
Completed 500 requests
Completed 600 requests
Completed 700 requests
Completed 800 requests
Completed 900 requests
Completed 1000 requests
Finished 1000 requests

Server Software:        nginx
Server Hostname:        demo.livehelperchat.com
Server Port:            80

Document Path:          /index.php/chat/syncuser/6/22/1e16f65d63f270401f90082a6fac9f3200ddab5d
Document Length:        103 bytes

Concurrency Level:      5
Time taken for tests:   5.349 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Total transferred:      462000 bytes
HTML transferred:       103000 bytes
Requests per second:    186.94 [#/sec] (mean)
Time per request:       26.746 [ms] (mean)
Time per request:       5.349 [ms] (mean, across all concurrent requests)
Transfer rate:          84.34 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:    15   27  17.0     24     235
Waiting:       15   27  17.0     24     235
Total:         15   27  17.0     24     235

Percentage of the requests served within a certain time (ms)
  50%     24
  66%     25
  75%     27
  80%     28
  90%     35
  95%     41
  98%     52
  99%     73
 100%    235 (longest request)

As you see application can handle about 180 requests per second. Having in mind that this request during chat is send every 3.5 seconds. We can support upto 600 chatting users at the same time if my calculations are correct :) (180*3.5 = 630)