changeset 26013:38f92d12357c

copy: add flag for disabling copy tracing

Copy tracing can be up to 80% of rebase time when rebasing stacks of commits in
large repos (hundreds of thousands of files).  This provides the option of
turning off the majority of copy tracing. It does not turn off _forwardcopies()
since that is used to carry copy information inside a commit across a rebase.

This will affect the situation where a user edits a file, then rebases on top of
commits that have moved that file. The move will not be detected and the user
will have to manually resolve the issue (possibly by redoing the rebase with
this flag off).

The reason to have a flag instead of trying to fix the actual copy tracing
performance is that copy tracing is fundamentally an O(number of files in the
repo) operation.  In order to know if file X in the rebase source was copied
anywhere, we have to walk the filelog for every new file that exists in the
rebase destination (i.e. a file in the destination that is not in the common
ancestor).  Without an index that lets us trace forward (i.e. from file Y in the
common ancestor forward to the rebase destination), it will never be an O(number
of changes in my branch) operation.

In mozilla-central, rebasing a 3 commit stack across 20,000 revs goes from 39s
to 11s.

--- a/mercurial/copies.py	Tue Aug 11 15:06:02 2015 -0400
+++ b/mercurial/copies.py	Tue Jan 27 11:26:27 2015 -0800
@@ -191,6 +191,9 @@
     return cm
 
 def _backwardrenames(a, b):
+    if a._repo.ui.configbool('experimental', 'disablecopytrace'):
+        return {}
+
     # Even though we're not taking copies into account, 1:n rename situations
     # can still exist (e.g. hg cp a b; hg mv a c). In those cases we
     # arbitrarily pick one of the renames.
@@ -264,6 +267,12 @@
     if c2.node() is None and c1.node() == repo.dirstate.p1():
         return repo.dirstate.copies(), {}, {}, {}
 
+    # Copy trace disabling is explicitly below the node == p1 logic above
+    # because the logic above is required for a simple copy to be kept across a
+    # rebase.
+    if repo.ui.configbool('experimental', 'disablecopytrace'):
+        return {}, {}, {}, {}
+
     limit = _findlimit(repo, c1.rev(), c2.rev())
     if limit is None:
         # no common ancestor, no copies
@@ -513,7 +522,12 @@
     copies between fromrev and rev.
     '''
     exclude = {}
-    if skiprev is not None:
+    if (skiprev is not None and
+        not repo.ui.configbool('experimental', 'disablecopytrace')):
+        # disablecopytrace skips this line, but not the entire function because
+        # the line below is O(size of the repo) during a rebase, while the rest
+        # of the function is much faster (and is required for carrying copy
+        # metadata across the rebase anyway).
         exclude = pathcopies(repo[fromrev], repo[skiprev])
     for dst, src in pathcopies(repo[fromrev], repo[rev]).iteritems():
         # copies.pathcopies returns backward renames, so dst might not

--- a/tests/test-copy-move-merge.t	Tue Aug 11 15:06:02 2015 -0400
+++ b/tests/test-copy-move-merge.t	Tue Jan 27 11:26:27 2015 -0800
@@ -59,4 +59,107 @@
   1
   2
 
+Test disabling copy tracing
+
+- first verify copy metadata was kept
+
+  $ hg up -qC 2
+  $ hg rebase --keep -d 1 -b 2 --config extensions.rebase=
+  rebasing 2:add3f11052fa "other" (tip)
+  merging b and a to b
+  merging c and a to c
+
+  $ cat b
+  0
+  1
+  2
+
+- next verify copy metadata is lost when disabled
+
+  $ hg strip -r . --config extensions.strip=
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  saved backup bundle to $TESTTMP/t/.hg/strip-backup/550bd84c0cd3-fc575957-backup.hg (glob)
+  $ hg up -qC 2
+  $ hg rebase --keep -d 1 -b 2 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 2:add3f11052fa "other" (tip)
+  remote changed a which local deleted
+  use (c)hanged version or leave (d)eleted? c
+
+  $ cat b
+  1
+  2
+
   $ cd ..
+
+Verify disabling copy tracing still keeps copies from rebase source
+
+  $ hg init copydisable
+  $ cd copydisable
+  $ touch a
+  $ hg ci -Aqm 'add a'
+  $ touch b
+  $ hg ci -Aqm 'add b, c'
+  $ hg cp b x
+  $ echo x >> x
+  $ hg ci -qm 'copy b->x'
+  $ hg up -q 1
+  $ touch z
+  $ hg ci -Aqm 'add z'
+  $ hg log -G -T '{rev} {desc}\n'
+  @  3 add z
+  |
+  | o  2 copy b->x
+  |/
+  o  1 add b, c
+  |
+  o  0 add a
+  
+  $ hg rebase -d . -b 2 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 2:6adcf8c12e7d "copy b->x"
+  saved backup bundle to $TESTTMP/copydisable/.hg/strip-backup/6adcf8c12e7d-ce4b3e75-backup.hg (glob)
+  $ hg up -q 3
+  $ hg log -f x -T '{rev} {desc}\n'
+  3 copy b->x
+  1 add b, c
+
+  $ cd ../
+
+Verify we duplicate existing copies, instead of detecting them
+
+  $ hg init copydisable3
+  $ cd copydisable3
+  $ touch a
+  $ hg ci -Aqm 'add a'
+  $ hg cp a b
+  $ hg ci -Aqm 'copy a->b'
+  $ hg mv b c
+  $ hg ci -Aqm 'move b->c'
+  $ hg up -q 0
+  $ hg cp a b
+  $ echo b >> b
+  $ hg ci -Aqm 'copy a->b (2)'
+  $ hg log -G -T '{rev} {desc}\n'
+  @  3 copy a->b (2)
+  |
+  | o  2 move b->c
+  | |
+  | o  1 copy a->b
+  |/
+  o  0 add a
+  
+  $ hg rebase -d 2 -s 3 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 3:47e1a9e6273b "copy a->b (2)" (tip)
+  saved backup bundle to $TESTTMP/copydisable3/.hg/strip-backup/47e1a9e6273b-2d099c59-backup.hg (glob)
+
+  $ hg log -G -f b
+  @  changeset:   3:76024fb4b05b
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     copy a->b (2)
+  |
+  o  changeset:   0:ac82d8b1f7c4
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     add a
+