tests/test-walkrepo.py

obsolete: order of magnitude speedup in _computebumpedset

Reminder: a changeset is said "bumped" if it tries to obsolete a immutable
          changeset.


The previous algorithm for computing bumped changeset was:

    1) Get all public changesets
    2) Find all they successors
    3) Search for stuff that are eligible for being "bumped"
       (mutable and non obsolete)

The entry size of this algorithm is `O(len(public))` which is mostly the same as
`O(len(repo))`. Even this this approach mean fewer obsolescence marker are
traveled, this is not very scalable.

The new algorithm is:

    1) For each potential bumped changesets (non obsolete mutable)
    2) iterate over precursors
    3) if a precursors is public. changeset is bumped

We travel more obsolescence marker, but the entry size is much smaller since
the amount of potential bumped should remains mostly stable with time `O(1)`.

On some confidential gigantic repo this move bumped computation from 15.19s to
0.46s (×33 speedup…). On "smaller" repo (mercurial, cubicweb's review) no
significant gain were seen. The additional traversal of obsolescence marker is
probably probably counter balance the advantage of it.

Other optimisation could be done in the future (eg: sharing precursors cache
for divergence detection)

import os
from mercurial import hg, ui
from mercurial.scmutil import walkrepos
from mercurial.util import checklink
from os import mkdir, chdir
from os.path import join as pjoin

u = ui.ui()
sym = checklink('.')

hg.repository(u, 'top1', create=1)
mkdir('subdir')
chdir('subdir')
hg.repository(u, 'sub1', create=1)
mkdir('subsubdir')
chdir('subsubdir')
hg.repository(u, 'subsub1', create=1)
chdir(os.path.pardir)
if sym:
    os.symlink(os.path.pardir, 'circle')
    os.symlink(pjoin('subsubdir', 'subsub1'), 'subsub1')

def runtest():
    reposet = frozenset(walkrepos('.', followsym=True))
    if sym and (len(reposet) != 3):
        print "reposet = %r" % (reposet,)
        print ("Found %d repositories when I should have found 3"
               % (len(reposet),))
    if (not sym) and (len(reposet) != 2):
        print "reposet = %r" % (reposet,)
        print ("Found %d repositories when I should have found 2"
               % (len(reposet),))
    sub1set = frozenset((pjoin('.', 'sub1'),
                         pjoin('.', 'circle', 'subdir', 'sub1')))
    if len(sub1set & reposet) != 1:
        print "sub1set = %r" % (sub1set,)
        print "reposet = %r" % (reposet,)
        print "sub1set and reposet should have exactly one path in common."
    sub2set = frozenset((pjoin('.', 'subsub1'),
                         pjoin('.', 'subsubdir', 'subsub1')))
    if len(sub2set & reposet) != 1:
        print "sub2set = %r" % (sub2set,)
        print "reposet = %r" % (reposet,)
        print "sub1set and reposet should have exactly one path in common."
    sub3 = pjoin('.', 'circle', 'top1')
    if sym and sub3 not in reposet:
        print "reposet = %r" % (reposet,)
        print "Symbolic links are supported and %s is not in reposet" % (sub3,)

runtest()
if sym:
    # Simulate not having symlinks.
    del os.path.samestat
    sym = False
    runtest()