Apache Friends Support Forum

Where is the configuration file for mod_mem_cache? I don't see anything in httpd.conf or any extra config files associated with it.

Feel free to insert the configuration lines wherever you want, either directly in httpd.conf or in an external file and include that file in httpd.conf

Nobbie wrote:Feel free to insert the configuration lines wherever you want, either directly in httpd.conf or in an external file and include that file in httpd.conf

Thanks.
I noticed the mod_mem_cache module is loaded in the httpd.conf file so I assumed it was "running" using a default configuration. The html web site files do indeed seem to be cached. I guess this must be linux caching the files. Is there a significant performance gain using mod_mem_cache in addition to the linux cache ?

I've read that mod_disk_cache is faster than mod_mem_cache. I wonder if there is a significant performance gain using mod_disk_cache in addition to the linux cache ?

I guess this must be linux caching the files.

Linux is not caching files.

But maybe your browser (or proxy, or web application) is doing this.

so I assumed it was "running" using a default configuration.

Correct. (and the default for mod_cache is to cache nothing)

Thanks for your quick reply. You replied faster than I could finish my post.

I added a question about mod_mem_cache vs mod_disk_cache.

Anyway... you commented that linux does not cache files. Seems to me the linux kernel uses a disk file cache to speed up disk access. Am I missing something here?

bigpcman wrote:Seems to me the linux kernel uses a disk file cache to speed up disk access. Am I missing something here?

Linux file system (i.e. extfs2/3, reiserfs etc.) is a caching file system, but caching does not take place on file level, but (one layer beyond) on block level. A block is the smallest unit of disk I/O. Block size depends on disk size and number of blocks, it is determined during disk format ("mkfs" command in linux/unix).

The cache is builtin in the file system driver, i.e. in the linux kernel. You cannot configure or modify it, it is used automatically.

As I am not really a fan of stacked cachings (usually the most powerfull caching is done by the OS), i dont think that there is a measurable performance gain by using several stacking algorithms at different levels/layers. You should run some benchmarks on your system to find out, if additional caching really raises performanceof your webserver.