view tests/test-demandimport.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

from mercurial import demandimport
demandimport.enable()

import re

rsub = re.sub
def f(obj):
    l = repr(obj)
    l = rsub("0x[0-9a-fA-F]+", "0x?", l)
    l = rsub("from '.*'", "from '?'", l)
    l = rsub("'<[a-z]*>'", "'<whatever>'", l)
    return l

import os

print "os =", f(os)
print "os.system =", f(os.system)
print "os =", f(os)

from mercurial import util

print "util =", f(util)
print "util.system =", f(util.system)
print "util =", f(util)
print "util.system =", f(util.system)

import re as fred
print "fred =", f(fred)

import sys as re
print "re =", f(re)

print "fred =", f(fred)
print "fred.sub =", f(fred.sub)
print "fred =", f(fred)

print "re =", f(re)
print "re.stderr =", f(re.stderr)
print "re =", f(re)