D4099: narrow: move .hg/narrowspec to .hg/store/narrowspec (BC)

[pulkit (Pulkit Goyal)]

pulkit added a comment.


  In https://phab.mercurial-scm.org/D4099#64270, @durin42 wrote:
  
  > In https://phab.mercurial-scm.org/D4099#64268, @pulkit wrote:
  >
  > > In https://phab.mercurial-scm.org/D4099#64266, @durin42 wrote:
  > >
  > > > There are non-Google users of narrow at this point (recall we've gotten non-Googler patches), so please publish the temporary migration hack someplace for the benefit of the other users.
  > > >
  > > > (A phabricator review that we immediately abandon would probably be fine, but we should definitely make a note in the relnotes for 4.8)
  > >
  > >
  > > Yes, we might roll-out narrow with mercurial 4.7 first, so this script will be of great help. (BTW, isn't it just a move of file?)
  >
  >
  > It's "just" a move, but typically the way we handle these migrations at Google is we write an extension that does one of the following:
  >
  > 1. Hijacks reads for the new file and reads the old file
  > 2. Hijacks reads for the new file if it doesn't exist and moves the new file
  >
  >   we run in mode 1 when we're doing the rollout and might roll back, then switch to mode 2 when we're past the rubicon on the rollout and can finalize the data migration. Once everyone has run the extension in mode 2 for a while, we reap the extension.
  
  
  Oh, I missed that clients need to be updated in real time. It will really be great if this extension is shared. Thanks @durin42 for the explanation.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D4099

To: martinvonz, durin42, #hg-reviewers
Cc: pulkit, yuja, mercurial-devel