Re: questions about MinUptimeHidServDirectoryV2 in 0.2.1.2-alpha

[Scott Bennett <bennett@xxxxxxxxxx>]

     On Tue, 05 Aug 2008 15:01:06 +0200 Karsten Loesing
<karsten.loesing@xxxxxxx> wrote:
>|      The tor man page says,
>|
>| 	"MinUptimeHidServDirectoryV2 N seconds|minutes|hours|days|weeks
>| 		Minimum  uptime  of a v2 hidden service directory to be accepted
>| 		as such by authoritative directories. (Default: 24 hours)"
>|
>| My questions are, what is the justification for the default of 24
>hours?  And
>| why have this particular option at all?  Why not instead have a "no longer
>| fresh/up to date" indicator somewhere, much like the fresh-until line for
>| consensus/status documents, so that a server that beomes disconnected
>or goes
>| down for only a brief time will remain available to provide hidden service
>| directory service as much of the time as possible?  Or, better yet,
>why not
>| simply handle this issue the same way that it is handled for normal
>directory
>| (mirror) service?
>
>The default of 24 hours ensures that hidden service directories are
>available for the next few hours with a certain probability. The idea is
>that there are hundreds of hidden service directories at some point
>which are not authoritative any more, but provide a more scalable and
>robust storage than the three authoritative ones can. Hidden services
>and clients need to have a view as consistent as possible of which
>hidden service directories are out there, so that clients can find
>previously stored hidden service descriptors. The 24 hours have turned

     How is that different from the situation of normal directory mirrors?

>out to be a characteristic that allows distinguishing highly available
>relays from others. The rationale behind it is that a certain number of
>relay operators turn their relays off over night. The following diagram

     In other words, it is already covered by the "Guard" and "Stable"
flags from the authorities, right?

>shows the variation of relays with different minimum uptimes over an
>interval of 2+ months. You can see the difference between minimum
>uptimes of 16 hours and lower and those of 20 hours and higher. That is
>the reason for the default of 24 hours.
>
>http://freehaven.net/~karsten/dirnodesminuptime.pdf

      It's very pretty, but, given the legend, which I assume denotes
uptimes in hours, the axis labels are not helpful.  What exactly do
"Directory Size" and "Time Index" refer to?
>
>The option MinUptimeHidServDirectoryV2 is mainly there to perform tests
>with the distributed hidden service directory without having to wait for
>24 hours. It is not required to set it in the public Tor network. (It
>only has an effect on directory authorities anyway.)

     I understand that, though it is also useful for the operators of the
current authorities should the policy change.  What I still don't see is
the need for a 24-hour delay before a server stops being only potentially
useful and becomes actually useful.  Earlier today the HSDir count was
down to only *4*.  How is it thus helpful to keep other servers from being
available for use?
>
>I should probably make the design paper of the distributed hidden
>service directory available rather soon. It answers questions like yours.
>
>Hope that helps!

     Not particularly at present, but I'll revisit your graph after I find
out what your labels mean.


                                  Scott Bennett, Comm. ASMELG, CFIAG
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