Is a nginx thread locked until the query completes?

Question

I have a nginx with 4 threads. The nginx is in front of 5 mongrels. Sometimes a query a mongrel is running takes very long. If 4 such queries occur simultaneously does that mean that all 4 threads of nginx are busy and will lock out further requests until a thread is free?

Answer 1

As far as I know nginx threads serve multiple connections, multiplexing them by syscalls (like "epol" and "kqueue"). So, while it loops it would check syscalls to return something from backends sometimes, but it would certainly be able to reply to clients.