# Proxy\_cache **URL:** \ **Category:** NGINX\ **Created:** [April 24, 2011, 4:59pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166 "2011-04-24T16:59:37Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\ **Post date:** [April 24, 2011, 4:59pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/1 "2011-04-24T16:59:37Z")
Hi Is there a way to know if a file has been cached/is currently being downloaded to cache without requesting the file? I.e. can I query the cache table somehow? I am trying to stop new files being written multiple times to disk when they are requested more than once at the same time (currently a new file can be being written 10’s of times to disk at once which kills the server) Many thanks as always ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 25, 2011, 4:12am UTC](https://www.ruby-forum.com/t/proxy-cache/206166/2 "2011-04-25T04:12:08Z")
On Sunday, April 24, 2011, Richard K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Is there a way to know if a file has been cached/is currently being downloaded > to cache without requesting the file? > I.e. can I query the cache table somehow? > I am trying to stop new files being written multiple times proxy\_cache\_use\_stale updating; > **[GitHub - nginxinc/nginx-wiki: ARCHIVED -- Source for the now archived NGINX Wiki...](https://github.com/nginxinc/nginx-wiki)** > > ARCHIVED -- Source for the now archived NGINX Wiki section of https://www.nginx.com – RPM ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 25, 2011, 4:22am UTC](https://www.ruby-forum.com/t/proxy-cache/206166/3 "2011-04-25T04:22:41Z")
Thanks, I already set “proxy\_cache\_use\_stale updating” But what if the file is completely new…? there is no stale file to serve ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 25, 2011, 8:57pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/4 "2011-04-25T20:57:03Z")
Hello! On Mon, Apr 25, 2011 at 02:22:23AM +0000, Richard K. wrote: > Thanks, I already set “proxy\_cache\_use\_stale updating” > But what if the file is completely new..? there is no stale file to serve Currently, there is no good way to handle this. Solution is usually called “busy locks” (search list archives for details), but it’s not ready yet. Maxim D. ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 25, 2011, 9:00pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/5 "2011-04-25T21:00:09Z")
On Sun, Apr 24, 2011 at 9:22 PM, Richard K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Thanks, I already set “proxy\_cache\_use\_stale updating” > But what if the file is completely new..? there is no stale file to serve Ah, I see… the first request for a new file would put it into the updating state, but there would be no stale version to serve. I’m not sure what happens in that case, but I would suspect that all of those requests go to the back end. This should be a very short-lived condition though. In the majority of the cases we’re talking milliseconds, unless the files are really large or the back-end is really slow. Say you had a 50 MB video file and your back-end was something like Amazon S3… I could see many many requests for that file coming in at the same time the first was still processing. I’m not sure what the best thing to do in that case would be. The options, I think, would be: 1. return a 404 (or some temporary error code) until the cache is primed (that doesn’t seem like good default behavior) 2. block all other requests until the first is finished (also seems problematic, especially if the first request is taking forever) 3. pass all requests to the back-end until there is a valid cache entry I suspect nginx chooses option #3. Are you saying that you want to do #2? Or something else entirely? Varnish seems to do #2 by default: > **[404 Page not found](https://www.varnish.org/docs/tutorial/handling_misbehaving_servers.html)** > > Varnish is a powerful, flexible HTTP accelerator that speeds up web applications by caching content and optimizing delivery. – RPM ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 25, 2011, 10:13pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/6 "2011-04-25T22:13:44Z")
Ideal situation is initiate one request to back-end then for each additional request start sending the (still incomplete) cached file at the same rate it’s being downloaded into the cache (I cache after just 1 hit) I’m talking video files 400-500mb crossing the Atlantic… Not fast at all and can get seriously congested once it starts getting the same file over and over in this “first cache” syndrome Anything I can do to help/test please let me know 🙂 Keep up the good work Sent from my iPhone ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 26, 2011, 4:29pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/7 "2011-04-26T16:29:12Z")
Hehe, I actually came up with the same conclusion… except that I’m running varnish in front of nginx Interestingly varnish has added a feature in their super-latest development version that streams and caches at the same time, but it only does it for the first request (subsequent requests still wait until the cache has been completed)… ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 26, 2011, 4:24pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/8 "2011-04-26T16:24:52Z")
On Mon, Apr 25, 2011 at 3:13 PM, Richard K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Ideal situation is initiate one request to back-end then for each additional > request start sending the (still incomplete) cached file at the same rate it’s > being downloaded into the cache (I cache after just 1 hit) > > I’m talking video files 400-500mb crossing the Atlantic… Not fast at all and > can get seriously congested once it starts getting the same file over and over in > this “first cache” syndrome > > Anything I can do to help/test please let me know 🙂 > Keep up the good work If this is an immediate problem (i.e. it is killing your monthly bandwidth bill), I would suggest setting up varnish behind nginx, and add a specific location for the video files in question. It will give you behavior closer to what you need (only making one request for the file over the slow link). You could then choose to expand varnish usage to other files after careful testing. This will complicate your stack, but such is life. Varnish just meets your particular use case better at this point. I’m no C developer, just an nginx user, but I suspect any change in this area would be a lot of work and slow in coming for nginx. I think it might be possible to do something all-nginx by having nginx proxy to itself for these files, and using something like [GitHub - nginxinc/nginx-wiki: ARCHIVED -- Source for the now archived NGINX Wiki section of https://www.nginx.com · GitHub](http://wiki.nginx.org/HttpLimitReqModule) on the “backend” nginx server which then proxies to your real origin… but it would be kind of hackish. – RPM ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 26, 2011, 5:20pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/9 "2011-04-26T17:20:29Z")
On 25 Abr 2011 21h13 WEST, removed\_email\_address@domain.invalid wrote: Just thinking out loud. Perhaps you can avoid using Varnish altogether and staying purely nginx by using agentzh’s Embedded Lua Module. Just an idea. — appa ---
**Author:** ![rkoskela](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ce73a5/32.png) [@rkoskela](https://www.ruby-forum.com/u/rkoskela)\ **Post date:** [April 29, 2011, 3:03pm UTC](https://www.ruby-forum.com/t/proxy-cache/206166/10 "2011-04-29T15:03:58Z")
I already use it for somethings… But what way would you use it to fix this problem? It can do a lot of things lol…