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[or-cvs] r9993: Describe a simpler implementation for proposal 108, and note (in tor/trunk: . doc/spec/proposals)
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- Subject: [or-cvs] r9993: Describe a simpler implementation for proposal 108, and note (in tor/trunk: . doc/spec/proposals)
- From: nickm@xxxxxxxx
- Date: Fri, 20 Apr 2007 13:17:15 -0400 (EDT)
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Date: 2007-04-20 13:17:13 -0400 (Fri, 20 Apr 2007)
New Revision: 9993
r12760@Kushana: nickm | 2007-04-20 11:23:21 -0400
Describe a simpler implementation for proposal 108, and note some limitations in the proposal.
Property changes on: tor/trunk
svk:merge ticket from /tor/trunk [r12760] on c95137ef-5f19-0410-b913-86e773d04f59
--- tor/trunk/doc/spec/proposals/108-mtbf-based-stability.txt 2007-04-19 19:52:30 UTC (rev 9992)
+++ tor/trunk/doc/spec/proposals/108-mtbf-based-stability.txt 2007-04-20 17:17:13 UTC (rev 9993)
@@ -23,17 +23,17 @@
Replace the current rule for setting the Stable flag with:
- "Stable" -- A router is 'Stable' if it is active and its observed MTBF
- for the past month is at or above the median MTBF for active routers.
+ "Stable" -- A router is 'Stable' if it is active and its observed Stability
+ for the past month is at or above the median Stability for active routers.
Routers are never called stable if they are running a version of Tor
known to drop circuits stupidly. (0.1.1.10-alpha through 0.1.1.16-rc
are stupid this way.)
- MTBF shall be defined as the mean length of the runs observed by a
+ Stability shall be defined as the mean length of the runs observed by a
given directory authority. A run begins when an authority decides
that the server is Running, and ends when the authority decides that
the server is not Running. In-progress runs are counted when
- measuring MTBF.
+ measuring Stability.
@@ -44,3 +44,18 @@
Surely somebody has done this kinds of thing before.
+ "A router's Stability shall be defined as the sum of $alpha ^ d$ for every
+ $d$ such that the router was not observed to be unavailable $d$ days ago."
+ This allows a simpler implementation: every day, we multiply yesterday's
+ Stability by alpha, and if the router was running for all of today, we add
+ Authorities can have false positives and false negatives when trying to
+ tell whether a router is up or down. So long as these aren't terribly
+ wrong, and so long as they aren't significantly biased, we should be able
+ to use them to estimate stability pretty well.