Maxim,

I dug a bit deeper and here is the nginx access log showing the 499 status request, and then a repost of the same request:

XX.XX.XXX.253 - - [06/Jun/2013:21:09:08 -0700] "POST /actions/execute.php HTTP/1.1" 499 0 "https://dev.mydomain.com/execute" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.110 Safari/537.36"

XX.XXX.XXX.253 - - [06/Jun/2013:21:11:32 -0700] "POST /actions/execute.php HTTP/1.1" 200 673 "https://dev.mydomain.com/execute" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.110 Safari/537.36"

I obviously need a solution, since I am essentially creating duplicate transactions. This only happens when the execute.php takes a long time though. In jQuery when I am making the AJAX request I am setting the timeout to 15 minutes. Is there anything else I can look at or try?

Thanks for the help.