Hi Amos,
On Sat, 25 Apr 2009, Amos Jeffries wrote:
>> ipcache_low 90
>> # ipcache_high 95
>> ipcache_high 95
>> cache_mem 1024 MB
>> # cache_swap_low 90
>> cache_swap_low 90
>> # cache_swap_high 95
>> cache_swap_high 95
>
> For cache >1GB the difference of 5% between high/low can mean long
> periods spent garbage-collecting the disk storage. This is a major drag.
> You can shrink the gap if you like less disk delay there.
Could you elaborate on this a little? If I understand correctly from the
comments in the template squid.conf:
(swap_usage < cache_swap_low)
-> no cache removal
(cache_swap_low < swap_usage < cache_swap_high)
-> cache removal attempts to maintain (swap_usage == cache_swap_log)
(swap_usage ~> cache_swap_high)
-> cache removal becomes aggressive until (swap_usage == cache_swap_log)
It seems like you're saying that aggressive removal is a big drag on the
disk so you should hit it early rather than late so the drag is not for
a long period. Would it be better to calculate an absolute figure (say
200MB) and work out what percentage of your cache that is? It seems like
the 95% high watermark is probably quite low for large caches too?
I have 2x400GB caches. A 5% gap would leave 20GB to delete aggressively
which might take quite some time alright. A 500MB gap would be 0.125.
cache_swap_low 97.875
cache_swap_high 98
Can we use floating point numbers here? Would it make more sense for squid
to offer absolute watermarks (in MB offset from the total size)?
Gavin
