view tests/test-requires.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 t
  $ cd t
  $ echo a > a
  $ hg add a
  $ hg commit -m test
  $ rm .hg/requires
  $ hg tip
  abort: index 00changelog.i unknown format 2!
  [255]
  $ echo indoor-pool > .hg/requires
  $ hg tip
  abort: unknown repository format: requires features 'indoor-pool' (upgrade Mercurial)!
  [255]
  $ echo outdoor-pool >> .hg/requires
  $ hg tip
  abort: unknown repository format: requires features 'indoor-pool', 'outdoor-pool' (upgrade Mercurial)!
  [255]

  $ cd ..