view tests/test-double-merge.t @ 26945:8a256cee72c8 stable

tags: create new sortdict for performance reasons

sortdict internally maintains a list of keys in insertion order. When a
key is replaced via __setitem__, we .remove() from this list. This
involves a linear scan and array adjustment. This is an expensive
operation.

The tags reading code was calling into sortdict.__setitem__ for each tag
in a read .hgtags revision. For repositories with thousands of tags or
thousands of .hgtags revisions, the overhead from list.remove()
noticeable.

This patch creates a new sortdict() so __setitem__ calls don't incur a
list.remove.

This doesn't appear to have any performance impact on my Firefox
repository. But that's only because tags reading doesn't show up in
profiles to begin with. I'm still waiting to hear from a user with over
10,000 tags and hundreds of heads on the impact of this patch.

  $ hg init repo
  $ cd repo

  $ echo line 1 > foo
  $ hg ci -qAm 'add foo'

copy foo to bar and change both files
  $ hg cp foo bar
  $ echo line 2-1 >> foo
  $ echo line 2-2 >> bar
  $ hg ci -m 'cp foo bar; change both'

in another branch, change foo in a way that doesn't conflict with
the other changes
  $ hg up -qC 0
  $ echo line 0 > foo
  $ hg cat foo >> foo
  $ hg ci -m 'change foo'
  created new head

we get conflicts that shouldn't be there
  $ hg merge -P
  changeset:   1:484bf6903104
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     cp foo bar; change both
  
  $ hg merge --debug
    searching for copies back to rev 1
    unmatched files in other:
     bar
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     src: 'foo' -> dst: 'bar' *
    checking for directory renames
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: e6dc8efe11cc, local: 6a0df1dad128+, remote: 484bf6903104
   preserving foo for resolve of bar
   preserving foo for resolve of foo
   bar: remote copied from foo -> m (premerge)
  picked tool ':merge' for bar (binary False symlink False)
  merging foo and bar to bar
  my bar@6a0df1dad128+ other bar@484bf6903104 ancestor foo@e6dc8efe11cc
   premerge successful
   foo: versions differ -> m (premerge)
  picked tool ':merge' for foo (binary False symlink False)
  merging foo
  my foo@6a0df1dad128+ other foo@484bf6903104 ancestor foo@e6dc8efe11cc
   premerge successful
  0 files updated, 2 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

contents of foo
  $ cat foo
  line 0
  line 1
  line 2-1

contents of bar
  $ cat bar
  line 0
  line 1
  line 2-2

  $ cd ..