Serving stale items from cache

[Andrew Alexeev]

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

On Sep 1, 2011, at 9:48 AM, Erik Wickstrom wrote:

> 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
> 
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