Hello!

On Thu, May 04, 2017 at 02:50:53AM -0400, Michael Corn wrote:

> I'm trying to limit the overall disk usage for the cache + any temp files.
>
> I have specified:
> proxy_cache_path /tmp/cache max_size=50m
> use_temp_path=off;
> proxy_max_temp_file_size 1m;
>
> Yet, what I observe is that the temp file will grow to the full size of the
> file being retrieved from the upstream, ignoring the value of
> proxy_max_temp_file_size, and ignoring the max_size for the cache. Only
> after the file is brought over completely does the cache manager kick in and
> delete something older from the cache to bring it back in line with the 50mb
> limit.
>
> For example, if I had in the cache file1 (20 MB) and file2 (20 MB), and I
> receive a request for file3 which is 20 MB, the total size of the /tmp/cache
> directory will grow to 60 MB. Only after file3 is received in its entirety
> will file1 be deleted bringing the size back down to 40 MB.
>
> I don't mind setting use_temp_path=on, but in that case as well the temp
> file grows beyond the proxy_max_temp_file_size.
>
> Any advice?

What you are trying to do is not going to work.

First of all, proxy_max_temp_file_size is ignored when using
cache. Quoting http://nginx.org/r/proxy_max_temp_file_size:

: This restriction does not apply to responses that will be cached
: or stored on disk.

As for the cache max_size parameter, it is maintained by the cache
manager process, and it does so after the files are already in
the cache. Quoting http://nginx.org/r/proxy_cache_path:

: The special "cache manager" process monitors the maximum cache
: size set by the max_size parameter. When this size is exceeded, it
: removes the least recently used data.

Moreover, cache manager may be busy with other tasks or just
sleeping, so there is inevitable difference between max_size
configured and possible maximum size of the cache.

--
Maxim Dounin
http://nginx.org/
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