view tests/test-issue1175.t @ 32200:4d504e541d3d

rebase: use matcher to optimize manifestmerge

The old merge code would call manifestmerge and calculate the complete diff
between the source to the destination. In many cases, like rebase, the vast
majority of differences between the source and destination are irrelevant
because they are differences between the destination and the common ancestor
only, and therefore don't affect the merge. Since most actions are 'keep', all
the effort to compute them is wasted.

Instead, let's compute the difference between the source and the common ancestor
and only perform the diff of those files against the merge destination. When
using treemanifest, this lets us avoid loading almost the entire tree when
rebasing from a very old ancestor. This speeds up rebase of an old stack of 27
commits by 20x.

In mozilla-central, without treemanifest, when rebasing a commit from
default~100000 to default, this speeds up the manifestmerge step from 2.6s to
1.2s.  However, the additional diff adds an overhead to all manifestmerge calls,
especially for flat manifests. When rebasing a commit from default~1 to default
it appears to add 100ms in mozilla-central. While we could put this optimization
behind a flag, I think the fact that it makes merge O(number of changes being
applied) instead of O(number of changes between X and Y) justifies it.

https://bz.mercurial-scm.org/1175

  $ hg init
  $ touch a
  $ hg ci -Am0
  adding a

  $ hg mv a a1
  $ hg ci -m1

  $ hg co 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg mv a a2
  $ hg up
  note: possible conflict - a was renamed multiple times to:
   a2
   a1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg ci -m2

  $ touch a
  $ hg ci -Am3
  adding a

  $ hg mv a b
  $ hg ci -Am4 a

  $ hg ci --debug --traceback -Am5 b
  committing files:
  b
  warning: can't find ancestor for 'b' copied from 'a'!
  committing manifest
  committing changelog
  committed changeset 5:83a687e8a97c80992ba385bbfd766be181bfb1d1

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  4 files, 6 changesets, 4 total revisions

  $ hg export --git tip
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 83a687e8a97c80992ba385bbfd766be181bfb1d1
  # Parent  1d1625283f71954f21d14c3d44d0ad3c019c597f
  5
  
  diff --git a/b b/b
  new file mode 100644

https://bz.mercurial-scm.org/show_bug.cgi?id=4476

  $ hg init foo
  $ cd foo
  $ touch a && hg ci -Aqm a
  $ hg mv a b
  $ echo b1 >> b
  $ hg ci -Aqm b1
  $ hg up 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg mv a b
  $ echo b2 >> b
  $ hg ci -Aqm b2
  $ hg graft 1
  grafting 1:5974126fad84 "b1"
  merging b
  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]
  $ echo a > b
  $ echo b3 >> b
  $ hg resolve --mark b
  (no more unresolved files)
  continue: hg graft --continue
  $ hg graft --continue
  grafting 1:5974126fad84 "b1"
  warning: can't find ancestor for 'b' copied from 'a'!
  $ hg log -f b -T 'changeset:   {rev}:{node|short}\nsummary:     {desc}\n\n'
  changeset:   3:376d30ccffc0
  summary:     b1
  
  changeset:   2:416baaa2e5e4
  summary:     b2
  
  changeset:   0:3903775176ed
  summary:     a