# How does FastCGI work under the covers? **URL:** \ **Category:** NGINX\ **Created:** [June 30, 2013, 11:11pm UTC](https://www.ruby-forum.com/t/how-does-fastcgi-work-under-the-covers/235568 "2013-06-30T23:11:57Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [June 30, 2013, 11:11pm UTC](https://www.ruby-forum.com/t/how-does-fastcgi-work-under-the-covers/235568/1 "2013-06-30T23:11:57Z")
Hello Everybody, I have a simple question about the Nginx FastCGI implementation. Let’s say that 1,000 web browsers are requesting pages from our server, and we’re using FastCGI within Nginx. While the FastCGI specification permits sending little pieces of each request (“multiplexing” them), my understanding is that most (all?) implementations don’t do this. Therefore, (1) does Nginx FastCGI provide exactly one complete HTTP request at a time? (2) does Nginx FastCGI want us to respond to that particular HTTP request before it gives us the next one? The reason that I ask is this: If my FastCGI server is high-latency, I’m wondering if it can get lots of requests to work on, or if it will have to finish one and only then get the next one, and only Nginx knows the answer to this question. 🙂 Many thanks for your kind help, and I hope that I didn’t miss the answer to this question in my search of the archives. kgk Posted at Nginx Forum: > **[How does FastCGI work under the covers?](https://forum.nginx.org/read.php?2,240429,240429#msg-240429)** > > Hello Everybody, I have a simple question about the Nginx FastCGI implementation. Let's say that 1,000 web browsers are requesting pages from our server, and we're using FastCGI within Nginx. While the FastCGI specification permits sending little... ---
**Author:** ![kgk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/edb3f5/32.png) [@kgk](https://www.ruby-forum.com/u/kgk)\ **Post date:** [July 1, 2013, 12:36am UTC](https://www.ruby-forum.com/t/how-does-fastcgi-work-under-the-covers/235568/2 "2013-07-01T00:36:04Z")
Hello! On Sun, Jun 30, 2013 at 05:10:23PM -0400, kgk wrote: > (1) does Nginx FastCGI provide exactly one complete HTTP request at a > time? > > (2) does Nginx FastCGI want us to respond to that particular HTTP request > before it gives us the next one? > > The reason that I ask is this: If my FastCGI server is high-latency, I’m > wondering if it can get lots of requests to work on, or if it will have to > finish one and only then get the next one, and only Nginx knows the answer > to this question. 🙂 FastCGI multiplexing isn’t used by nginx. That is, within a single connection to a fastcgi application only one request is sent, and then nginx will wait for a response. More connections will be opened if there are multiple simulteneous requests. – Maxim D. > **[nginx: donation](http://nginx.org/en/donation.html)** ---
**Author:** ![kgk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/edb3f5/32.png) [@kgk](https://www.ruby-forum.com/u/kgk)\ **Post date:** [July 1, 2013, 6:21pm UTC](https://www.ruby-forum.com/t/how-does-fastcgi-work-under-the-covers/235568/3 "2013-07-01T18:21:08Z")
Hello Maxim, Thank you so much for answering my previous questions! Now I have a few more: 1. Will Nginx provide a FastCGI request only when it is 100% complete, i.e., the browser has provided every necessary byte? 2. Will Nginx always accept 100% of a FastCGI response and hold it inside internal buffers (or on disk), and not wait for the client (= web browser)? kgk Maxim D. Wrote: * * * > * * * > > nginx mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [mailman.nginx.org archive](http://mailman.nginx.org/mailman/listinfo/nginx) Posted at Nginx Forum: [http://forum.nginx.org/read.php?2,240429,240453#msg-240453](http://forum.nginx.org/read.php?2,240429,240453#msg-240453) ---
**Author:** ![kgk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/edb3f5/32.png) [@kgk](https://www.ruby-forum.com/u/kgk)\ **Post date:** [July 1, 2013, 7:09pm UTC](https://www.ruby-forum.com/t/how-does-fastcgi-work-under-the-covers/235568/4 "2013-07-01T19:09:02Z")
Hello! On Mon, Jul 01, 2013 at 11:57:21AM -0400, kgk wrote: > Hello Maxim, > > Thank you so much for answering my previous questions! Now I have a few > more: > > 1. Will Nginx provide a FastCGI request only when it is 100% complete, > i.e., the browser has provided every necessary byte? Yes. > 1. Will Nginx always accept 100% of a FastCGI response and hold it inside > internal buffers (or on disk), and not wait for the client (= web browser)? Depends on configuration, see [Module ngx\_http\_fastcgi\_module](http://nginx.org/r/fastcgi_max_temp_file_size). – Maxim D. > **[nginx: donation](http://nginx.org/en/donation.html)**