[GHC] #15938: Hadrian's recompilation check is extremely slow

[GHC]

#15938: Hadrian's recompilation check is extremely slow
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.8.1
       Component:  Build System      |              Version:  8.6.2
  (Hadrian)                          |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by NeilMitchell):

 Shake records cached oracles immediately and even if the build fails (but
 not if the parsing of the metadata fails, as you might expect). I'd treat
 the pause and the slow rebuild as entirely separate issues, since they
 likely have different causes. Of these, slow rebuild is the easiest one to
 reproduce - generally you shouldn't be running any command line tools
 during a rebuild, and if you do, you failed to cache something properly.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15938#comment:8>
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