Re: [RFC] byte hit ratio

On 08.02.2012 07:48, Alex Rousskov wrote:
> On 02/07/2012 05:00 AM, Amos Jeffries wrote:
>> On 7/02/2012 9:40 p.m., Henrik Nordström wrote:
>>> tis 2012-02-07 klockan 14:01 +1300 skrev Amos Jeffries:
>>>> We have a long history of questions and bugs mentioning negative
>>>> numbers in the byte hit ratio.
>>>>
>>>> I've always thought it was a bug we had not tracked down, but the
>>>> FAQ
>>>> says it is correct.
>>>>
>>>> http://wiki.squid-cache.org/SquidFaq/InnerWorkings#Why_do_I_see_negative_byte_hit_ratio.3F
>>>>
>>> Yes.. it's based on the difference between traffic squid<-servers
>>> and
>>> clients<-squid. This can be negative (more traffic squid<-servers
>>> than
>>> clients<-squid) in some situations.
>>>
>>> - retried requests
>>> - range retreival being processed by Squid
>>> - continued download after client disconnects (quick_abort_...)
>>
>> Wiki also mentions cache digests but ...
>> " /*
>> * This ugly hack is here to prevent the user from seeing a
>> * negative byte hit ratio. When we fetch a cache digest from
>> * a neighbor, it gets treated like a cache miss because the
>> * object is consumed internally. Thus, we subtract cache
>> * digest bytes out before calculating the byte hit ratio.
>> */
>> cd = CountHist[0].cd.kbytes_recv.kb -
>> CountHist[minutes].cd.kbytes_recv.kb;
>> "
>
> I think that hack should be removed (why would we want to lie about
> bandwidth usage?) but I may be missing some deeper reasons why it was
> added.
>
>>
>> Which one is inaccurate?
>> "Hits as % of traffic sent" with calculation of (net traffic /
>> client
>> bytes)
>> or
>> "Net traffic gain/loss" with calculation of (net traffic /
>> client_bytes)
>> or
>> "Hits as % of client traffic" with calculation of ( sum_hits /
>> client_bytes )
>>
>> One guess which one we have today ...
>
> I think the bandwidth G/L formula should be something like:
>
> (client - server) / client
>
> Note how it is independent from the definition of what a "hit" is.

This is my proposals point exactly.

PS. in the above, "net traffic" == (client - server)

>
> The name is a separate question.
>
> We could use a similar formula to report "hit ratio" as well (just
> use
> message counts instead of bytes) but that would be somewhat against
> the
> "standard practice". I am not against adding a separate "message G/L"
> line for that.

Okay. So if I get this you are in favour of only a text change.

Amos
Received on Tue Feb 07 2012 - 22:52:13 MST