[squid-users] rock storage and max-swap-rate

[Alex Rousskov]

On 01/18/2018 05:35 PM, Ivan Larionov wrote:

> * Multiple squid swap in or swap out ops reading/writing contiguous
> blocks could be merged into one 256KB IO operation.

> * Random squid operations could be handled as single 32KB IO operation.

FWIW, on a busy Squid with a large disk cache in a stable state, there
should be virtually no mergeable/contiguous swap requests (first bullet)
due to random nature of rock slot assignment.

Alex.


> On Thu, Jan 18, 2018 at 3:20 PM, Amos Jeffries wrote:
> 
>     On 19/01/18 12:04, Ivan Larionov wrote:
> 
>         Thank you for the fast reply!
> 
>         read_ops and write_ops is AWS EBS metric and in general it
>         correlates with OS-level reads/s writes/s stats which iostat shows.
> 
>         So if I understand you correctly max-swap-rate doesn't limit
>         disk IOPS but limits squid swap ops instead and every squid
>         operation could in theory use more than 1 disk IO operation.
>         This means we can't really say "limit swap ops to 1500 because
>         our disk can handle 1500 iops" but should figure out the number
>         after testing different values.
> 
>         Ok, I suppose I'll just do what Rock documentation says – will
>         test different values and figure out what works for us.
> 
> 
> 
>     If you know what the OS level IOP size is (eg usually 4KB) and the
>     Squid rock IOP size Alex mentioned of 32KB. That should give you a
>     number to divide the disk IOPS limit you want with to get a rough
>     estimate for the appropriate Squid setting.
> 
>     The tuning bit is just to see how much variance from that is caused
>     by your traffic objects being different from the 32KB slot size.
> 
> 
>     Amos
> 
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> 
> 
> -- 
> With best regards, Ivan Larionov.
> 
> 
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