annotate tests/test-merge5.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

  $ hg init
  $ echo This is file a1 > a
  $ echo This is file b1 > b
  $ hg add a b
  $ hg commit -m "commit #0"
  $ echo This is file b22 > b
  $ hg commit -m "comment #1"
  $ hg update 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm b
  $ hg commit -A -m "comment #2"
  removing b
  created new head
  $ hg update 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg update
  abort: crosses branches (merge branches or update --check to force update)
  [255]
  $ rm b
  $ hg update -c
  abort: uncommitted local changes
  [255]
  $ hg revert b
  $ hg update -c
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mv a c

In theory, we shouldn't need the "-y" below, but it prevents this test
from hanging when "hg update" erroneously prompts the user for "keep
or delete".

Should abort:

  $ hg update -y 1
  abort: crosses branches (merge branches or use --clean to discard changes)
  [255]
  $ mv c a

Should succeed:

  $ hg update -y 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved