[tahoe-lafs-trac-stream] [tahoe-lafs] #1382: immutable peer selection refactoring and enhancements

[tahoe-lafs]

#1382: immutable peer selection refactoring and enhancements
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     Reporter:  kevan    |      Owner:  markberger
         Type:           |     Status:  new
  enhancement            |  Milestone:  1.11.0
     Priority:  major    |    Version:  1.8.2
    Component:  code-    |   Keywords:  review-needed servers-of-happiness
  peerselection          |  blocks-release
   Resolution:           |
Launchpad Bug:           |
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Comment (by daira):

 Replying to [comment:62 zooko]:
 > So I suspect that is_happy_enough() isn't calculating exactly the right
 function, but we don't notice because it gets called only for well-
 distributed things, by test_upload, so "return True" also works for the
 current tests. (I tried this, and {{{return True}}} does indeed give the
 correct answer for all queries that test_upload.py sends to the
 {{{is_happy_enough}}} function.)
 > But it seems like we ought to replace it with a function that calculates
 the correct thing, to avoid confusing future test-writers.
 >
 > So Mark: please write a new {{{is_happy_enough}}}, or explain to me why
 I'm wrong, or replace the call to {{{is_happy_enough}}} with a call to
 {{{allmydata.util.happinessutil.servers_of_happiness}}}.

 Calling {{{allmydata.util.happinessutil.servers_of_happiness}}} from
 {{{is_happy_enough}}} and trusting the result would not preserve the
 intent of the test, because there might be a bug in {{{happinessutil}}}
 that would then propagate to the test and result in a false pass.

 Since the test only checks for happiness rather than unhappiness, it would
 be possible to call a function in {{{servers_of_happiness}}} that returns
 a purported maximum matching, and check that it actually is a matching. It
 is not necessary to check that the matching is maximum, because not being
 maximum could only cause the test to fail; it could not cause a false
 pass.

-- 
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1382#comment:65>
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