mercurial/discovery.py

revlog: improve delta generation heuristics for generaldelta

Without this change, pulls (and clones) into a generaldelta repository could
generate very inefficient revlogs, the size of which could be at least twice
the original size.

This was caused by the generated delta chains covering too large distances,
causing new chains to be built far too often. This change addresses the
problem by forcing a delta against second parent or against the previous
revision, when the first parent delta is in danger of creating a long chain.

# discovery.py - protocol changeset discovery functions
#
# Copyright 2010 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from node import nullid, short
from i18n import _
import util, setdiscovery, treediscovery

def findcommonincoming(repo, remote, heads=None, force=False):
    """Return a tuple (common, anyincoming, heads) used to identify the common
    subset of nodes between repo and remote.

    "common" is a list of (at least) the heads of the common subset.
    "anyincoming" is testable as a boolean indicating if any nodes are missing
      locally. If remote does not support getbundle, this actually is a list of
      roots of the nodes that would be incoming, to be supplied to
      changegroupsubset. No code except for pull should be relying on this fact
      any longer.
    "heads" is either the supplied heads, or else the remote's heads.

    If you pass heads and they are all known locally, the reponse lists justs
    these heads in "common" and in "heads".

    Please use findcommonoutgoing to compute the set of outgoing nodes to give
    extensions a good hook into outgoing.
    """

    if not remote.capable('getbundle'):
        return treediscovery.findcommonincoming(repo, remote, heads, force)

    if heads:
        allknown = True
        nm = repo.changelog.nodemap
        for h in heads:
            if nm.get(h) is None:
                allknown = False
                break
        if allknown:
            return (heads, False, heads)

    res = setdiscovery.findcommonheads(repo.ui, repo, remote,
                                       abortwhenunrelated=not force)
    common, anyinc, srvheads = res
    return (list(common), anyinc, heads or list(srvheads))

def findcommonoutgoing(repo, other, onlyheads=None, force=False, commoninc=None):
    '''Return a tuple (common, anyoutgoing, heads) used to identify the set
    of nodes present in repo but not in other.

    If onlyheads is given, only nodes ancestral to nodes in onlyheads (inclusive)
    are included. If you already know the local repo's heads, passing them in
    onlyheads is faster than letting them be recomputed here.

    If commoninc is given, it must the the result of a prior call to
    findcommonincoming(repo, other, force) to avoid recomputing it here.

    The returned tuple is meant to be passed to changelog.findmissing.'''
    common, _any, _hds = commoninc or findcommonincoming(repo, other, force=force)
    return (common, onlyheads or repo.heads())

def prepush(repo, remote, force, revs, newbranch):
    '''Analyze the local and remote repositories and determine which
    changesets need to be pushed to the remote. Return value depends
    on circumstances:

    If we are not going to push anything, return a tuple (None,
    outgoing) where outgoing is 0 if there are no outgoing
    changesets and 1 if there are, but we refuse to push them
    (e.g. would create new remote heads).

    Otherwise, return a tuple (changegroup, remoteheads), where
    changegroup is a readable file-like object whose read() returns
    successive changegroup chunks ready to be sent over the wire and
    remoteheads is the list of remote heads.'''
    commoninc = findcommonincoming(repo, remote, force=force)
    common, revs = findcommonoutgoing(repo, remote, onlyheads=revs,
                                      commoninc=commoninc, force=force)
    _common, inc, remoteheads = commoninc

    cl = repo.changelog
    outg = cl.findmissing(common, revs)

    if not outg:
        repo.ui.status(_("no changes found\n"))
        return None, 1

    if not force and remoteheads != [nullid]:
        if remote.capable('branchmap'):
            # Check for each named branch if we're creating new remote heads.
            # To be a remote head after push, node must be either:
            # - unknown locally
            # - a local outgoing head descended from update
            # - a remote head that's known locally and not
            #   ancestral to an outgoing head

            # 1. Create set of branches involved in the push.
            branches = set(repo[n].branch() for n in outg)

            # 2. Check for new branches on the remote.
            remotemap = remote.branchmap()
            newbranches = branches - set(remotemap)
            if newbranches and not newbranch: # new branch requires --new-branch
                branchnames = ', '.join(sorted(newbranches))
                raise util.Abort(_("push creates new remote branches: %s!")
                                   % branchnames,
                                 hint=_("use 'hg push --new-branch' to create"
                                        " new remote branches"))
            branches.difference_update(newbranches)

            # 3. Construct the initial oldmap and newmap dicts.
            # They contain information about the remote heads before and
            # after the push, respectively.
            # Heads not found locally are not included in either dict,
            # since they won't be affected by the push.
            # unsynced contains all branches with incoming changesets.
            oldmap = {}
            newmap = {}
            unsynced = set()
            for branch in branches:
                remotebrheads = remotemap[branch]
                prunedbrheads = [h for h in remotebrheads if h in cl.nodemap]
                oldmap[branch] = prunedbrheads
                newmap[branch] = list(prunedbrheads)
                if len(remotebrheads) > len(prunedbrheads):
                    unsynced.add(branch)

            # 4. Update newmap with outgoing changes.
            # This will possibly add new heads and remove existing ones.
            ctxgen = (repo[n] for n in outg)
            repo._updatebranchcache(newmap, ctxgen)

        else:
            # 1-4b. old servers: Check for new topological heads.
            # Construct {old,new}map with branch = None (topological branch).
            # (code based on _updatebranchcache)
            oldheads = set(h for h in remoteheads if h in cl.nodemap)
            newheads = oldheads.union(outg)
            if len(newheads) > 1:
                for latest in reversed(outg):
                    if latest not in newheads:
                        continue
                    minhrev = min(cl.rev(h) for h in newheads)
                    reachable = cl.reachable(latest, cl.node(minhrev))
                    reachable.remove(latest)
                    newheads.difference_update(reachable)
            branches = set([None])
            newmap = {None: newheads}
            oldmap = {None: oldheads}
            unsynced = inc and branches or set()

        # 5. Check for new heads.
        # If there are more heads after the push than before, a suitable
        # error message, depending on unsynced status, is displayed.
        error = None
        for branch in branches:
            newhs = set(newmap[branch])
            oldhs = set(oldmap[branch])
            if len(newhs) > len(oldhs):
                if error is None:
                    if branch:
                        error = _("push creates new remote heads "
                                  "on branch '%s'!") % branch
                    else:
                        error = _("push creates new remote heads!")
                    if branch in unsynced:
                        hint = _("you should pull and merge or "
                                 "use push -f to force")
                    else:
                        hint = _("did you forget to merge? "
                                 "use push -f to force")
                if branch:
                    repo.ui.debug("new remote heads on branch '%s'\n" % branch)
                for h in (newhs - oldhs):
                    repo.ui.debug("new remote head %s\n" % short(h))
        if error:
            raise util.Abort(error, hint=hint)

        # 6. Check for unsynced changes on involved branches.
        if unsynced:
            repo.ui.warn(_("note: unsynced remote changes!\n"))

    if revs is None:
        # use the fast path, no race possible on push
        cg = repo._changegroup(outg, 'push')
    else:
        cg = repo.getbundle('push', heads=revs, common=common)
    return cg, remoteheads