# Does Nginx block on file IO? **URL:** \ **Category:** NGINX\ **Created:** [May 2, 2011, 2:26am UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458 "2011-05-02T02:26:57Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\ **Post date:** [May 2, 2011, 2:26am UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/1 "2011-05-02T02:26:57Z")
Hi. I was always under the impression that Nginx is non-blocking for file IO. Then I was told it wasn’t. I’m considering using Nginx to serve static images. Pretty much every connection will result in a file IO. If Nginx blocks for file IO, then using Nginx here wouldn’t be any better than using Apache, right? Every connection will lead to a file IO which blocks the entire Nginx process. So to serve 500 concurrent connections I’ll need 500 Nginx processes. Would Nginx work in such a use case? Any tips on how to use Nginx for serving static media? Thanks. Posted at Nginx Forum: > **[Does Nginx block on file IO?](https://forum.nginx.org/read.php?2,194884,194884#msg-194884)** > > Hi. I was always under the impression that Nginx is non-blocking for file IO. Then I was told it wasn't. I'm considering using Nginx to serve static images. Pretty much every connection will result in a file IO. If Nginx blocks for file IO, then... ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 3:55am UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/2 "2011-05-02T03:55:11Z")
## Andy Wrote: > I was always under the impression that Nginx is > non-blocking for file IO. Then I was told it > wasn’t. Actually AIO support was added not so long ago. It can be non-blocking for file IO on systems with AIO. > If Nginx blocks for file IO, then > using Nginx here wouldn’t be any better than using > Apache, right? How is it even related? There is a difference between getting a file from disk and serving it to the client from buffer. You can get it really fast and block for a very little time but than send it to the client very slowly. So asynchronous front-end would be a really good idea. Other than that you might find that neither nginx nor apache can serve your images fast enough from any common filesystem. You will need something like Bitcask to go farther. The idea is to get an entire image to the buffer in a single disk seek. Posted at Nginx Forum: [http://forum.nginx.org/read.php?2,194884,194891#msg-194891](http://forum.nginx.org/read.php?2,194884,194891#msg-194891) ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 7:23am UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/3 "2011-05-02T07:23:42Z")
Hi, > I was always under the impression that Nginx is non-blocking for file > IO. Then I was told it wasn’t. That depends on your configuration on on capabilities of your operating system. Asynchronous file I/O is available on recent versions of Linux, Solaris, DragonFly, FreeBSD, NetBSD, MacOSX. > I’m considering using Nginx to serve static images. Pretty much every > connection will result in a file IO. No, it won’t. Recently served files should be in your OS’s buffer cache. > If Nginx blocks for file IO, then > using Nginx here wouldn’t be any better than using Apache, right? Every > connection will lead to a file IO which blocks the entire Nginx process. > So to serve 500 concurrent connections I’ll need 500 Nginx processes. If that would be the case (buffer cache hit rate would be very low) and you would be using magnetic disks, then yes, you’d be better off with a web server than uses per-client lightweight processes or threads. Best regards, Piotr S. \< [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) \> ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 7:30am UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/4 "2011-05-02T07:30:29Z")
Hi, > How is it even related? There is a difference between getting a file > from disk and serving it to the client from buffer. You can get it > really fast and block for a very little time but than send it to the > client very slowly. It’s actually very related, because with event-driven programming, you’re blocking _all_ worker’s clients on the single disk I/O. Best regards, Piotr S. \< [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) \> ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 1:17pm UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/5 "2011-05-02T13:17:50Z")
## Piotr S. Wrote: > It’s actually very related, because with > event-driven programming, you’re > blocking _all_ worker’s clients on the single disk > I/O. I know, but imagine how much memory you can save and use for file system cache if you are not running apache. Which can make fat more greater impact on your performance. You can’t just say that nginx is the same as apache just because it’s blocking on file I/O. So still, it depends on the type of load you are having. And if you are not serving 100 megabytes of data to 500 clients but a lot more you are most likely to get better results with asynchronous server even with blocking file I/O. Posted at Nginx Forum: [http://forum.nginx.org/read.php?2,194884,194939#msg-194939](http://forum.nginx.org/read.php?2,194884,194939#msg-194939) ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 1:06pm UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/6 "2011-05-02T13:06:41Z")
On Mon, 2011-05-02 at 07:29 +0200, Piotr S. wrote: > Hi, > > > How is it even related? There is a difference between getting a file > > from disk and serving it to the client from buffer. You can get it > > really fast and block for a very little time but than send it to the > > client very slowly. > > It’s actually very related, because with event-driven programming, you’re > blocking _all_ worker’s clients on the single disk I/O. If you expect file IO to block, use more nginx processes than cores. I dont think that async IO on Linux is really worth using, although I will do some benchmarks. You might try switching to FreeBSD as well. I think that node.js currently uses a thread pool for async IO on Linux (possibly all platforms, except maybe Windows), with sync IO in the background. Linux kernel aio was designed for programs like databases that manage their own buffer caches, not for normal file IO. If you dont cache the results it will be slow (unless anything has changed recently, will do some testing). Justin ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 8:11pm UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/7 "2011-05-02T20:11:31Z")
On Sun, 2011-05-01 at 20:26 -0400, Andy wrote: > Hi. > > I was always under the impression that Nginx is non-blocking for file > IO. Then I was told it wasn’t. > > I’m considering using Nginx to serve static images. Pretty much every > connection will result in a file IO. If Nginx blocks for file IO, then > using Nginx here wouldn’t be any better than using Apache, right? Every > connection will lead to a file IO which blocks the entire Nginx process. > So to serve 500 concurrent connections I’ll need 500 Nginx processes. You cannot take a single measure such as concurrent requests independent of requests per second and make a good prediction about performance requirements. If you have 500 concurrent requests, and each request takes an average of 1ms, then you could conceivably serve all 500 requests within 0.5 seconds with a single worker, which is quite reasonable. People have reported serving 10K requests per second using Nginx on rather modest hardware (laptops even). You’ll probably find that your OS is the bottleneck, not Nginx (and you should focus your performance tuning at that level - TCP buffers and the like). It’s also worth pointing out that if you currently have 500 concurrent requests on Apache, that number may actually decrease with Nginx, assuming requests are finished faster (i.e. if Nginx finishes each request twice as fast as Apache, you’d only see 250 concurrent requests, while requests per second would double). Obviously that’s simplified, but hopefully clarifies my point. In any case, no need to have a worker per request, just start with the recommendation of 1 worker per core and tune from there. It’s true that the _concurrent_ number of requests is limited by the number of workers you have (the remaining requests will be served serially as each worker is freed), but in practice, it becomes academic. Serialization is going to happen at some level, even if you have a threaded server, so basically software threads buy you little more than the feeling of concurrency at the cost of massive amounts of memory. > Would Nginx work in such a use case? Any tips on how to use Nginx for > serving static media? Serving static content is actually where Nginx has been demonstrated to outperform Apache by a wide margin, in no small part because it leaves lots of memory for filesystem caching, and also because it causes less context-switches than a threaded server. At the end of the day, you should do some performance testing, since performance is going to depend a lot on factors that will only be revealed on your particular setup and your particular data (number and size of files, cache misses, etc). Regards, Cliff ---
**Author:** ![andy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@andy](https://www.ruby-forum.com/u/andy)\ **Post date:** [May 2, 2011, 1:26pm UTC](https://www.ruby-forum.com/t/does-nginx-block-on-file-io/206458/8 "2011-05-02T13:26:29Z")
## jjjx128 Wrote: > And if you are not serving 100 megabytes > of data to 500 clients but a lot more you are most > likely to get better results with asynchronous > server even with blocking file I/O. Sorry, bad example, in this case your data will fit in file system cache and you still will be better off with nginx bacuase of all the context switches you save. Anyway there might be some very special case where disks are overloaded and access patterns are truly random. Although this never happens in real world. Posted at Nginx Forum: [http://forum.nginx.org/read.php?2,194884,194941#msg-194941](http://forum.nginx.org/read.php?2,194884,194941#msg-194941)