[squid-users] What are recommended settings for optimal sharing of cache between SMP workers?

Hello,

Need some guidance for optimal sharing of cache amongst SMP workers
using Large rock.

Context:

I am using squid cache with 8 SMP workers and a 200 GB rock cache stored on SMP.
(Using squid-3.HEAD-20140127-r13248 which has LargeRock support to
cache objects > 32 KB).

I have set :
maximum_object_size 4 MB
cache_dir rock /mnt/squid-cache 204800 max-size=4194304
cache_mem 0 MB

My refresh pattern is very permissive which basically allows caching everything:
refresh_pattern . 129600 100% 129600 ignore-auth

Questions:

I am trying to test optimal caching behavior where after I have
downloaded 1 GB data (~16000 objects ~64KB each) the subsequent
download should all be cache hits.
However, I see several TCP misses in access.log. The hit ratio on
subsequent download of the same objects is ~85%.

1. Is this expected in a multiple worker setup? If yes, can you please
briefly explain what contributes towards these misses and how can this
be minimized?

2. I set cache_mem to 0 coz I believe cache_mem sharing is
opportunistic and hence all workers might not always share all objects
in cache_mem. Is that correct? What impact does cache_mem size have on
deterministic sharing of cache between workers.

3. Moreover are there any tips/guidelines to optimize % hit rate for
previously downloaded objects.

Thanks,
Rajiv
Received on Tue Feb 18 2014 - 09:52:28 MST