# Serving stale items from cache **URL:** \ **Category:** NGINX\ **Created:** [September 1, 2011, 7:49am UTC](https://www.ruby-forum.com/t/serving-stale-items-from-cache/211315 "2011-09-01T07:49:41Z")\ **Posts on this page:** 5\ **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:** [September 1, 2011, 7:49am UTC](https://www.ruby-forum.com/t/serving-stale-items-from-cache/211315/1 "2011-09-01T07:49:41Z")
I have a web application where the objects are expensive to generate, yet each individual object is accessed infrequently (a few times a week). The dataset in total is about 24 GB. Can Nginx be configured to cache these items for a short amount of time (say 20 minutes), but also have a relatively long (i.e. 7 days) stale setting so clients will always get a fast response (but at the same time will trigger an update of the cached item). proxy\_cache\_path /var/lib/nginx/cache levels=2:2:2 keys\_zone=staticfilecache:512m inactive=7d max\_size=25000m; # serve stale cache when the cache is updating, or there is a timeout or error. proxy\_cache\_use\_stale timeout updating error invalid\_header http\_500 http\_502 http\_503 http\_504; proxy\_cache\_valid 200 20m; My understanding is that the by setting proxy\_cache\_path to inactive=7d, cached items will be kept for 7 days and available to be served as stale objects. Basically any request that comes in after 20 minutes will get a stale object from the cache for up to 7 days (and at the same time refresh the cache with the latest version from the backend). However, in testing, it appears that stale objects are not returned, but instead a fresh request is made to my appservers. Here is some sample data from my logs (Notice the $upstream\_cache\_status and $request\_time at the end of the log line) 71.111.3.11 - - [31/Aug/2011:19:44:26 +0000] “GET /?p=3093 HTTP/1.1” 200 3849 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.215 Safari/535.1” - EXPIRED 15.789 71.111.3.11 - - [31/Aug/2011:19:44:42 +0000] “GET /?p=3093 HTTP/1.1” 200 3849 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.215 Safari/535.1” - HIT 0.000 71.111.3.11 - - [31/Aug/2011:19:51:02 +0000] “GET /?p=3093 HTTP/1.1” 200 3849 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.215 Safari/535.1” - HIT 0.000 71.111.3.11 - - [31/Aug/2011:20:01:50 +0000] “GET /?p=3093 HTTP/1.1” 200 3849 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.215 Safari/535.1” - HIT 0.000 71.111.3.11 - - [31/Aug/2011:21:03:56 +0000] “GET /?p=3093 HTTP/1.1” 200 3851 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1” - EXPIRED 0.725 71.111.3.11 - - [31/Aug/2011:21:14:55 +0000] “GET /?p=3093 HTTP/1.1” 200 3851 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1” - HIT 0.000 71.111.3.11 - - [31/Aug/2011:21:54:18 +0000] “GET /?p=3093 HTTP/1.1” 200 3833 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1” - EXPIRED 0.856 71.111.3.11 - - [31/Aug/2011:22:01:25 +0000] “GET /?p=3093 HTTP/1.1” 200 3833 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1” - HIT 0.000 71.111.3.11 - - [01/Sep/2011:00:02:01 +0000] “GET /?p=3093 HTTP/1.1” 200 3847 “-” “Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_7\_1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1” - MISS 11.019 Basically I’m trying to keep my cache warm, without overwhelming my app servers. Is this doable? Thanks! Erik ---
**Author:** ![Erik\_Wickstrom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/3ab097/32.png) [@Erik\_Wickstrom](https://www.ruby-forum.com/u/Erik_Wickstrom)\ **Post date:** [September 2, 2011, 6:00pm UTC](https://www.ruby-forum.com/t/serving-stale-items-from-cache/211315/2 "2011-09-02T18:00:23Z")
Erik, That’s not currently doable with nginx. Proxy\_cache\_use\_stale directive works when you’ve got your backend down. What you want is more like doing a triggered update of the content in background and it’s not possible at this time. Hope this helps ---
**Author:** ![Erik\_Wickstrom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/3ab097/32.png) [@Erik\_Wickstrom](https://www.ruby-forum.com/u/Erik_Wickstrom)\ **Post date:** [September 22, 2011, 10:04pm UTC](https://www.ruby-forum.com/t/serving-stale-items-from-cache/211315/3 "2011-09-22T22:04:33Z")
I would love to see this too in Nginx. The pattern is described here: [Two HTTP Caching Extensions](http://www.mnot.net/blog/2007/12/12/stale) The only software I’ve seen this implemented in is Squid 2.7 (stale-while-revalidate). From time to time I see backends taking 800ms+ to generate a page at low traffic. It would be nice to hide most of these requests to the end user. Posted at Nginx Forum: > **[Re: Serving stale items from cache](https://forum.nginx.org/read.php?2,214606,215654#msg-215654)** > > I have a web application where the objects are expensive to generate, yet each individual object is accessed infrequently (a few times a week). The dataset in total is about 24 GB. Can Nginx be configured to cache these items for a short amount of... ---
**Author:** ![Erik\_Wickstrom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/3ab097/32.png) [@Erik\_Wickstrom](https://www.ruby-forum.com/u/Erik_Wickstrom)\ **Post date:** [September 23, 2011, 1:05am UTC](https://www.ruby-forum.com/t/serving-stale-items-from-cache/211315/4 "2011-09-23T01:05:38Z")
proxy\_cache\_use\_stale updating does soemthing similar. You may could do something like (from the docs) proxy\_cache\_bypass $http\_my\_secret\_header; without a corresponding proxy\_no\_cache and that should make nginx go to the origin server but cache the results. –Brian ---
**Author:** ![Erik\_Wickstrom](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/3ab097/32.png) [@Erik\_Wickstrom](https://www.ruby-forum.com/u/Erik_Wickstrom)\ **Post date:** [September 22, 2011, 11:10pm UTC](https://www.ruby-forum.com/t/serving-stale-items-from-cache/211315/5 "2011-09-22T23:10:05Z")
I ended up using Varnish for this. I set a long TTL for the cache, and then another long “grace” period for those expired objects. Then I use a script to loop through all of my URLs and rewarm the cache every few days. [https://www.varnish-cache.org/trac/wiki/VCLExampleHashAlwaysMiss](https://www.varnish-cache.org/trac/wiki/VCLExampleHashAlwaysMiss) Seems to be working.