Davi Arnaut wrote:
But that's a corner case. There is no reason in doing this for small files (common case). For example, in a enterprise grade server memory is cheap and permanent storage is slow and expensive.
If permanent storage is slow and expensive, what on earth is the admin doing trying to turn on a disk cache?
However luckily though the typical modern OS helps by RAM caching common disk access, the argument has been made here before that a disk cache gives same or better performance than the memory cache.
Please don't forget that mod_cache, by design, is a generic RFC2616 caching proxy bolted onto the frontend of the webserver, and that means you can cache virtually any well behaved application - from mod_perl, to CGI, to mod_python, mod_proxy, whatever.
And also don't forget that compared to the speed at which a webserver can generate data, the typical client is many orders of maginitude slower at swallowing that data. So your big expensive mod_perl, CGI, mod_python, etc sits around waiting for the client to get on with it and download the response, using resources better spent elsewhere.
A very common use case is for a caching proxy is to take the load off an expensive application server, and usually this is deployed as a separate piece of kit in front of the webserver. With mod_cache, you can offload this inside the server itself, which simplifies your setup.
In short, this is not a corner case.
Also, httpd seems to be faster delivering data by sendfile than delivering data from memory buckets. That's more of a performance bug in httpd though.It's not all httpd fault. Sendfile avoids memory copying/context switches/etc behind the scenes (in the kernel) because it "talks" directly to the underlying file system. When you have the memory already in user space there isn't much that you can do, the kernel has to copy it..etc.
Exactly - another strong argument to make sure that when you turn on the disk cache, you serve the network off the disk cache.
Regards, Graham --
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