[squid-users] Enable caching

[Alex Rousskov]

On 4/5/23 09:27, Alex Rousskov wrote:
> On 4/5/23 06:07, Andrey K wrote:
> 
>> Previously, caching was disabled on our proxy servers. Now we need to 
>> cache some content (files about 10 MB in size).
>> So we changed the squid.conf:
> 
>> cache_dir ufs /data/squid/cache 32000 16 256 max-size=12000000
>>
>> We have 24 workers on each proxy.
> 
> UFS-based cache_dirs are not supported in multi-worker configurations 
> and, in most cases, should not be used in such configurations. The 
> combination will violate basic HTTP caching rules and may crash Squid 
> and/or corrupt responses.
> 
> 
>> We saw that some requests were taken from the cache, and some were not.
>> The documentation says:
>> "In SMP configurations, cache_dir must not precede the workers option 
>> and should use configuration macros or conditionals to give each 
>> worker interested in disk caching a dedicated cache directory."
> 
> The official documentation quoted above is stale and very misleading in 
> modern Squids. Ignore it. I will try to find the time to post a PR to 
> fix this.

Done at https://github.com/squid-cache/squid/pull/1394

Alex.



>> So we switched to a rock cache_dir:
>> cache_dir rock /data/squid/cache 32000 max-size=12000000
>>
>> Now everything seems to be working fine in the test environment, but I 
>> found limitations on the RockStore 
>> (https://wiki.squid-cache.org/Features/RockStore:
>> "Objects larger than 32,000 bytes cannot be cached when cache_dirs are 
>> shared among workers."
> 
> The Feature/RockStore page is stale and can easily mislead. In general, 
> Feature/Foo wiki pages are often development-focused and get stale with 
> time. They cannot be reliably used as a Squid feature documentation.
> 
> 
>> Does this mean that RockStore is not suitable for caching large files?
> 
> No, it does not. Rock storage has evolved since that Feature page was 
> written. You can see the following wiki page discussing evolved rock 
> storage design, but that page probably has some stale info as well:
> https://wiki.squid-cache.org/Features/LargeRockStore
> 
> 
>> Should I switch back to the UFS and configure 24 cache_dirs
> 
> If everything is "working fine", then you should not. Otherwise, I 
> recommend discussing specific problems before switching to that 
> unsupported and dangerous hack.