Re: [squid-users] More on - How does (AUFS) squid decide which c

On 24-Aug-07 My Secret NSA Wiretap Overheard Henrik Nordstrom Saying :
> On fre, 2007-08-24 at 14:20 -0700, Nicole wrote:
>> > l2 = 256
>>
>> So, this should always be the same size?
>
> Yes, there is not much reason to change L2.
>
>> > L1 = at least cache_dir size * 2 / 256 / 256 / 13KB, or ca cache_dir in
>> > GB * 2. (13 KB is the estimated average object size)
>>
>> ca?
>
> yes? (circa) I rounded it a bit.. it's not an exact math. As long as it
> ends up in about those numbers.. L1 * L2 * L2 should be significantly
> more than the number of objects you have in the cache, and L2 should not
> be too big or too small.
>
>
>> I guess I am missing something?
>> 90000 * 2 / 256 / 256 = 2.746582 / 13000 = .0002112 ??
>
> You are missing an unit.. 90000 in the above should be 90000MB
>
> L1 = 90000MB * 2 / 256 / 256 / 13KB =
> 900000 * 1024 * 2 / 256 / 256 / 13 = 216
>
>> Could you provide an example or 2?
>
> simplified formula:
>
> L2 = 256
> L1 = cache_dir size / 500, rounded upwards on small numbers..
>
> If L2 is changed or you have a singnificantly different object size
> distribution then use the equation above. This simplified formula is
> only valid for L2 = 256 and average object size of about 13KB.
>
> Regards
> Henrik

 Wow, excellent, thank you.

 However, I would have thought the directory sizing would have slanted smaller.

 With this:
# cache_dir aufs Directory-Name Mbytes L1 L2 [options]
cache_dir aufs /cache0 24000 32 128
cache_dir aufs /cache1 90000 64 256
cache_dir aufs /cache2 90000 64 256
cache_dir aufs /cache3 90000 64 256

Each at about 80% of full (73 of 90G full)

 Holding:
Internal Data Structures:
        12450858 StoreEntries
        116215 StoreEntries with MemObjects
        116214 Hot Object Cache Items
        12,449,836 on-disk objects
        Mean Object Size: 12.43 KB

 I only have: (same on all dirs)
 ls -l /cache2/02/00 | wc -l = 257 files per dir

 So, perhaps should the formula then add a / by number of cache_dirs?
 Does it perhaps apply more assuming a single cache_dir?

 Or, does squid just really prefer more dirs to objects per dir?
 On FreeBSD, with things like directory hashing and such, I am curious how much
or who benefits from the larger tree.
 I would have thought it would like more per dir rather than less to keep
the dir table lookups smaller.

 Thanks for helping me understand more!

 Nicole

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