view tests/notcapable @ 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

# Disable the $CAP wire protocol capability.

if test -z "$CAP"
then
    echo "CAP environment variable not set."
fi

cat > notcapable-$CAP.py << EOF
from mercurial import extensions, peer, localrepo
def extsetup():
    extensions.wrapfunction(peer.peerrepository, 'capable', wrapcapable)
    extensions.wrapfunction(localrepo.localrepository, 'peer', wrappeer)
def wrapcapable(orig, self, name, *args, **kwargs):
    if name in '$CAP'.split(' '):
        return False
    return orig(self, name, *args, **kwargs)
def wrappeer(orig, self):
    # Since we're disabling some newer features, we need to make sure local
    # repos add in the legacy features again.
    return localrepo.locallegacypeer(self)
EOF

echo '[extensions]' >> $HGRCPATH
echo "notcapable-$CAP = `pwd`/notcapable-$CAP.py" >> $HGRCPATH