Martin,

On Jan 11, 2012, at 7:31 PM, Martin Loy wrote:

In some situations, mod_aclr2 helps to avoid excessive disk I/O, especially for big static responses.

When nginx is used as a local reverse proxy and proxy_buffering is enabled, every upstream reponse which can not fit into proxy buffers may be temporarily saved on disk:

http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_buffering http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_temp_path

For example, we have to process the request for 700mb video file, without mod_aclr2:

1) nginx sends the request to apache 2) apache sends 700mb file back to nginx 3) nginx saves received file on disk (proxy_temp_path) and starts sending it back to the client

and with mod_aclr2:

1) nginx sends the request to apache 2) apache sends a few bytes header with X-Accel-Redirect back to nginx 3) nginx starts sending the file directly from disk

You save your time and your disk at step #2.

Of course, you also may use proxy_cache along with mod_aclr2, but if your disks are fast enough, probably you won't need to do any caching at all.

Hope this helps.