view tests/test-convert-bzr-treeroot.t @ 17970:0b03454abae7

ancestor: faster algorithm for difference of ancestor sets

One of the major reasons rebase is slow in large repositories is
the computation of the detach set: the set of ancestors of the
changesets to rebase not in the destination parent. This is currently
done via a revset that does two walks all the way to the root of
the DAG. Instead of doing that, to find ancestors of a set <revs>
not in another set <common> we walk up the tree in reverse revision
number order, maintaining sets of nodes visited from <revs>, <common>
or both.

For the common case where the sets are close both topologically and
in revision number (relative to repository size), this has been
found to speed up rebase by around 15-20%. When the nodes are farther
apart and the DAG is highly branching, it is harder to say which
would win.

Here's how long computing the detach set takes in a linear repository
with over 400000 changesets, rebasing near tip:

Rebasing across 4 changesets
Revset method: 2.2s
New algorithm: 0.00015s

Rebasing across 250 changesets
Revset method: 2.2s
New algorithm: 0.00069s

Rebasing across 10000 changesets
Revset method: 2.4s
New algorithm: 0.019s

  $ . "$TESTDIR/bzr-definitions"
  $ cat > treeset.py <<EOF
  > import sys
  > from bzrlib import workingtree
  > wt = workingtree.WorkingTree.open('.')
  > 
  > message, rootid = sys.argv[1:]
  > wt.set_root_id('tree_root-%s' % rootid)
  > wt.commit(message)
  > EOF

change the id of the tree root

  $ mkdir test-change-treeroot-id
  $ cd test-change-treeroot-id
  $ bzr init -q source
  $ cd source
  $ echo content > file
  $ bzr add -q file
  $ bzr commit -q -m 'Initial add'
  $ python ../../treeset.py 'Changed root' new
  $ cd ..
  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial add
  0 Changed root
  $ manifest source-hg tip
  % manifest of tip
  644   file

  $ cd ..