Re: [squid-users] Optimal maximum cache size

Hi Amos,

Amos Jeffries wrote:
>> Is there such a thing as too much disk cache? Presumably squid has to
>> have some way of checking this cache, and at some point it takes longer
>> to look for a cached page than to serve it direct. At what point do you
>> hit that sort of problem, or is it so large no human mind should worry?
>> :)
>>
>> Paul
>> IT Systems Admin
>
> Disk cache is limited by access time and ironically RAM.
>
> Squid holds an in-memory index of 10MB-ram per GB-disk. With large disk
> caches this can fill RAM pretty fast, particularly if the cache is full of
> small objects. Large objects use less index space more disk.
>
> Some with smaller systems hit the limit at 20-100GB, others in cache farms
> reach TB.
>
> As for the speed of lookup vs DIRECT. If anyone has stats, please let us
> know.

I can't understand under what circumstances the cache Lookup will be
slower than DIRECT lookup unless one has a net connection faster than
the disks!

For a 20 GB cache with 1175539 on-disk objects:

Median Service Times (seconds) 5 min 60 min:
         HTTP Requests (All): 1.24267 1.38447
         Cache Misses: 1.54242 1.71839
         Cache Hits: 0.00919 0.00865
         Near Hits: 1.38447 1.62803
         Not-Modified Replies: 0.00179 0.00091
         DNS Lookups: 0.04237 0.04433
         ICP Queries: 0.00102 0.00096

The cache Lookup is 170 times faster than DIRECT lookups!

MAYBE, if I use a bigger cache say, 100-300 GB, the results could be
different. But I believe that running multiple Squid boxes with smaller
caches (10-30 GB) is always better than running 1 single Squid box with
a (100-300 GB) cache.

The benefits of running multiple smaller caches far outweigh running a
single large cache.

But this is only my opinion.

 From my guess and experience, to run a 300 GB cache, one needs about 6
GB of memory! But I can't imagine how to manage a 300 GB cache if it
gets corrupted!

Thanking you...

>
> Amos
>
>
>
>

-- 
With best regards and good wishes,
Yours sincerely,
Tek Bahadur Limbu
System Administrator
(TAG/TDG Group)
Jwl Systems Department
Worldlink Communications Pvt. Ltd.
Jawalakhel, Nepal
http://www.wlink.com.np
http://teklimbu.wordpress.com