On 03/27/2012 10:42 AM, Peter Gaughran wrote:
With the recent (enlightening) posts from Christian, Marcus et al, I was wondering what the metrics actually are for calculating cache_mem and cache_dir? I've read (for Linux at least) aufs is superior to diskd, so I've made the appropriate decision, but any time any reference is made to size of caches or directory depth, figures are mentioned that seem to be obeying formulae, but I've yet to find the actual formulae? Are they any other critical parameters I should be wary of, resource wise? I've had a look over the Squid wiki, and various other sources, but can't seem to find a definitive answer? Apologies if I'm being daft and missing something that's well known :) Our current setup is a 32 gig, single CPU (E5620) with 4 15k 300 gig disks available for disk cache (o/s is elsewhere).
I think there is no one-formula-fits-all since sites have different user groups which visit different sets of websites which have different caching patterns. Having said that, there are rules of thumb. There are various trade-offs: memory-cache vs disk-cache vs no-cache (retrieve again) speed vs investment no-cache can be faster than disk-cache but needs more bandwidth memory-cache is faster than disk-cache and no-cache From the above is seems logical to have a large memory-cache. Prices and specs of bandwidth vary. Based on your bandwidth you can decide where to invest: more bandwidth or very fast disks. If bandwidth is cheap, a server with only a memory cache and no disk cache can be a proper configuration. Squid is CPU bound and up to version 3.1.x is bound by the speed of a single CPU core. The not yet released 3.2 uses multiple cores. So currently, the faster the CPU, the better and the more cache a CPU has, the better. In your particular case with 4 high speed disks and 32 GB memory you could choose for 4 aufs cache directories: 1 per disk total disk cache of 300 GB (4,2 GB in-memory index) memory-cache of 22 GB This leaves 6 GB for all other resources: - other memory usage by Squid - other processes - OS including file system buffers and network buffers You need a very large swap for squid to be able to fork. At least 32 GB swap but I think that 64 GB is better. This is only a suggested setup. Always look carefully at the system behavior, especially swap. Marcus
