Hello! On Sun, May 16, 2021 at 04:46:17PM +0000, Lucas Rolff wrote:
> Hi everyone, > > I have a few questions regarding proxy_cache and the use of > proxy_cache_min_uses in nginx: > > Let’s assume you have an nginx server with proxy_cache enabled, > and you’ve set proxy_cache_min_uses to 5; > > Q1: How does nginx internally keep track of the count for > min_uses? Is it using SHM to do it (and counts towards the > key_zone limit?), or something else? > > Q2: How long time does nginx keep this information for the > number of accesses. Let’s say the file gets visited once in a 24 > hour period; Would nginx keep the counter at 1 for that whole > period, or are there some set timeout where it’s “flushed”. > > Q3: If you have a user who decides to access files with a random > query string on it; We want to prevent caching this to fill up > the storage (The main reason for setting the > proxy_cache_min_uses in the first place) – but are we gonna fill > up the memory (and keys_zone limit) regardless; If yes – is > there a way to prevent this? > > Basically the goal is to understand even just broadly how > min_uses are counted, and possibly how to prevent memory from > being eaten up in case someone decides to access the same URL > once with millions of requests – if there’s any way to flush out > the memory for example, for anything that haven’t yet reached > the proxy_cache_min_uses if it indeed uses up memory. The proxy_cache_min_uses basically means that if nginx sees a request whose uses count not reached the specified limit yet, it won't try to store the response to disk. It will, however, keep the key in the keys_zone with the relevant information, notably the number of uses seen so far. Quoting the proxy_cache_path directive description (http://nginx.org/r/proxy_cache_path): "In addition, all active keys and information about data are stored in a shared memory zone, whose name and size are configured by the keys_zone parameter. One megabyte zone can store about 8 thousand keys." Much like with any cache item, such keys are removed from the keys_zone if no matching requests are seen during the "inactive" time. Similarly, least recently used keys are removed if there is not enough room in the keys_zone. Much like with normal caching, you can control the cache key nginx uses. If you don't want to take query string into account, you may want to configure proxy_cache_key without the query string (see http://nginx.org/r/proxy_cache_key). -- Maxim Dounin http://mdounin.ru/ _______________________________________________ nginx mailing list nginx@nginx.org http://mailman.nginx.org/mailman/listinfo/nginx
