view tests/test-context.py @ 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

import os
from mercurial import hg, ui, context, encoding

u = ui.ui()

repo = hg.repository(u, 'test1', create=1)
os.chdir('test1')

# create 'foo' with fixed time stamp
f = open('foo', 'w')
f.write('foo\n')
f.close()
os.utime('foo', (1000, 1000))

# add+commit 'foo'
repo[None].add(['foo'])
repo.commit(text='commit1', date="0 0")

print "workingfilectx.date =", repo[None]['foo'].date()

# test memctx with non-ASCII commit message

def filectxfn(repo, memctx, path):
    return context.memfilectx("foo", "")

ctx = context.memctx(repo, ['tip', None],
                     encoding.tolocal("Gr\xc3\xbcezi!"),
                     ["foo"], filectxfn)
ctx.commit()
for enc in "ASCII", "Latin-1", "UTF-8":
    encoding.encoding = enc
    print "%-8s: %s" % (enc, repo["tip"].description())