diff mercurial/treediscovery.py @ 14164:cb98fed52495

discovery: add new set-based discovery

Adds a new discovery method based on repeatedly sampling the still
undecided subset of the local node graph to determine the set of nodes
common to both the client and the server.

For small differences between client and server, it uses about the same
or slightly fewer roundtrips than the old tree-based discovery. For
larger differences, it typically reduces the number of roundtrips
drastically (from 150 to 4, for instance).

The old discovery code now lives in treediscovery.py, the new code is
in setdiscovery.py.

Still missing is a hook for extensions to contribute nodes to the
initial sample. For instance, Augie's remotebranches could contribute
the last known state of the server's heads.

Credits for the actual sampler and computing common heads instead of
bases go to Benoit Boissinot.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/treediscovery.py	Mon May 02 19:21:30 2011 +0200
@@ -0,0 +1,151 @@
+# 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, error
+
+def findcommonincoming(repo, remote, heads=None, force=False):
+    """Return a tuple (common, fetch, 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.
+    "fetch" is a list of roots of the nodes that would be incoming, to be
+      supplied to changegroupsubset.
+    "heads" is either the supplied heads, or else the remote's heads.
+    """
+
+    m = repo.changelog.nodemap
+    search = []
+    fetch = set()
+    seen = set()
+    seenbranch = set()
+    base = set()
+
+    if not heads:
+        heads = remote.heads()
+
+    if repo.changelog.tip() == nullid:
+        base.add(nullid)
+        if heads != [nullid]:
+            return [nullid], [nullid], list(heads)
+        return [nullid], [], []
+
+    # assume we're closer to the tip than the root
+    # and start by examining the heads
+    repo.ui.status(_("searching for changes\n"))
+
+    unknown = []
+    for h in heads:
+        if h not in m:
+            unknown.append(h)
+        else:
+            base.add(h)
+
+    heads = unknown
+    if not unknown:
+        return list(base), [], []
+
+    req = set(unknown)
+    reqcnt = 0
+
+    # search through remote branches
+    # a 'branch' here is a linear segment of history, with four parts:
+    # head, root, first parent, second parent
+    # (a branch always has two parents (or none) by definition)
+    unknown = remote.branches(unknown)
+    while unknown:
+        r = []
+        while unknown:
+            n = unknown.pop(0)
+            if n[0] in seen:
+                continue
+
+            repo.ui.debug("examining %s:%s\n"
+                          % (short(n[0]), short(n[1])))
+            if n[0] == nullid: # found the end of the branch
+                pass
+            elif n in seenbranch:
+                repo.ui.debug("branch already found\n")
+                continue
+            elif n[1] and n[1] in m: # do we know the base?
+                repo.ui.debug("found incomplete branch %s:%s\n"
+                              % (short(n[0]), short(n[1])))
+                search.append(n[0:2]) # schedule branch range for scanning
+                seenbranch.add(n)
+            else:
+                if n[1] not in seen and n[1] not in fetch:
+                    if n[2] in m and n[3] in m:
+                        repo.ui.debug("found new changeset %s\n" %
+                                      short(n[1]))
+                        fetch.add(n[1]) # earliest unknown
+                    for p in n[2:4]:
+                        if p in m:
+                            base.add(p) # latest known
+
+                for p in n[2:4]:
+                    if p not in req and p not in m:
+                        r.append(p)
+                        req.add(p)
+            seen.add(n[0])
+
+        if r:
+            reqcnt += 1
+            repo.ui.progress(_('searching'), reqcnt, unit=_('queries'))
+            repo.ui.debug("request %d: %s\n" %
+                        (reqcnt, " ".join(map(short, r))))
+            for p in xrange(0, len(r), 10):
+                for b in remote.branches(r[p:p + 10]):
+                    repo.ui.debug("received %s:%s\n" %
+                                  (short(b[0]), short(b[1])))
+                    unknown.append(b)
+
+    # do binary search on the branches we found
+    while search:
+        newsearch = []
+        reqcnt += 1
+        repo.ui.progress(_('searching'), reqcnt, unit=_('queries'))
+        for n, l in zip(search, remote.between(search)):
+            l.append(n[1])
+            p = n[0]
+            f = 1
+            for i in l:
+                repo.ui.debug("narrowing %d:%d %s\n" % (f, len(l), short(i)))
+                if i in m:
+                    if f <= 2:
+                        repo.ui.debug("found new branch changeset %s\n" %
+                                          short(p))
+                        fetch.add(p)
+                        base.add(i)
+                    else:
+                        repo.ui.debug("narrowed branch search to %s:%s\n"
+                                      % (short(p), short(i)))
+                        newsearch.append((p, i))
+                    break
+                p, f = i, f * 2
+            search = newsearch
+
+    # sanity check our fetch list
+    for f in fetch:
+        if f in m:
+            raise error.RepoError(_("already have changeset ")
+                                  + short(f[:4]))
+
+    base = list(base)
+    if base == [nullid]:
+        if force:
+            repo.ui.warn(_("warning: repository is unrelated\n"))
+        else:
+            raise util.Abort(_("repository is unrelated"))
+
+    repo.ui.debug("found new changesets starting at " +
+                 " ".join([short(f) for f in fetch]) + "\n")
+
+    repo.ui.progress(_('searching'), None)
+    repo.ui.debug("%d total queries\n" % reqcnt)
+
+    return base, list(fetch), heads