[PATCH 1 of 3] add branchmap repository (and wire) command and capability
Sune Foldager
cryo at cyanite.org
Thu May 21 02:41:50 CDT 2009
# HG changeset patch
# User Sune Foldager <cryo at cyanite.org>
# Date 1242889818 -7200
# Node ID aa08c8294220bf4f5b8702c9353c6c13a64d73c2
# Parent 6062c6362b2e318fbc731d3aa1211b662d70c191
add branchmap repository (and wire) command and capability
The repository command, 'branchmap', returns a dictionary,
branchname -> [branchheads], and is implemented for localrepo, httprepo
and sshrepo.
The following wire format is used for returning data:
branchname1 branch1head2 branch1head2 ...
branchname2 ...
...
Branch names are URL encoded to escape white space, and branch heads are
sent as hex encoded node ids. All branches and all their heads are sent.
The background and motivation for this command is the desire for a
richer named branch semantics when pushing changesets. The details are
explained in the original proposal which is included below.
1. BACKGROUND
The algorithm currently implemented in Mercurial only considers the
graph theoretical heads when determining whether new heads are created,
rather than using the branch heads as a count (the algorithm considers a
branch head effectively closed when it is merged into another branch or
a new named branch is started from that point onward).
Our particular problem with the algorithm is that we'd like to see the
following case working without forcing a push:
Upsteam has:
(0:dev) ---- (1:dev)
\
`--- (2:stable)
Someone merges stable into dev:
(0:dev) ---- (1:dev) ------(3:dev)
\ /
`--- (2:stable) --------´
This can be pushed without --force (as it should).
Now someone else does some coding on stable (a bug fix, say):
(0:dev) ---- (1:dev) ------(3:dev)
\ /
`--- (2:stable) ---------´---------(4:stable)
This time we need --force to push.
We allow this to be pushed without using --force by getting all the
remote branch heads (by extending the wire protocol with a new
function).
We would, furthermore, also prefer if it is impossible to push a new
branch without --force (or a later --newbranch option so --force isn't
shoe-horned into too many disparate functions, if need be), except of
course in the case where the remote repository is empty.
This is what our patch accomplishes.
2. ALTERNATIVES
We have, of course, considered some alternatives to reconstructing
enough information to decide whether we are creating new remote branch
heads, before we added the new wire protocol command.
2.1. LOOKUP ON REMOTE
The main alternative is to use the information from remote.heads() and
remote.lookup() to try to reconstruct enough graph information to decide
whether we are creating new heads. This is not adequate as illustrated
below.
Remember that each lookup is typically a request-response pair over SSH
or HTTP(S).
If we have a simple repository at the remote end like this:
(0:dev) ---- (1:dev) ---- (3:stable)
\
`--- (2:dev)
then remote.heads() will yield [2, 3]. Assume we have nodes [0, 1, 2]
locally and want to create a new node, 4:dev, as a descendant from
(1:dev), which should be OK as 1:dev is a branch head.
If we do remote.lookup('dev') we will get [2]. Thus, we can get
information about whether a branch exists on the remote server or not,
but this does not solve our problem of figuring out whether we are
creating new heads or not.
Pushing 4:dev ought to be OK, since after the push, we still only have
two heads on branch a.
Using remote.lookup() and remote.heads() is thus not adequate to
consistently decide whether we are creating new remote heads (e.g. in
this situation the latter would never return 1:dev).
2.2. USING INCOMING TO RECONSTRUCT THE GRAPH
An alternative would be to use information equivalent to hg incoming to
get the full remote graph in addition to the local graph.
To do this, we would have to get a changegroup(subset) bundle
representing the remote end (which may be a substantial amount of data),
getting the branch heads from an instantiated bundlerepository, deleting
the bundle, and finally, we can compute the prepush logic.
While this is backwards compatible, it will cause a possibly substantial
slowdown of the push command as it first needs to pull in all changes.
3. FURTHER ARGUMENTS IN FAVOUR OF THE BRANCHMAP WIRE-PROTOCOL EXTENSION
Currently, the commands incoming and pull, work based on the tip of a
given branch if used with "-r branchname", making it hard to get all
revisions of a certain branch only (if it has multiple heads). This can
be solved by requesting the remote's branchheads and letting the
revisions to be used with the command be these heads. This can be done
by extending the commands with a new option, e.g.:
hg pull -b branchname
which will be turned into the equivalent of:
hg pull -r branchhead1 -r branchhead2 -r branchhead3
We have a simple follow-up patch that can do this ready as well
(although not submitted yet as it is pending the acceptance of the
branch patch).
4. WRAP-UP
We generally find that the branchmap wire protocol extension can provide
better named branch support to Mercurial. Currently, some things, like
the initial push scenario in this mail, are fairly counter-intuitive,
and the more often you have to force push, the more it is likely you
will get a lot of spurious and unnecessary merge nodes. Also,
restricting incoming and pull to all changes on a branch rather than
changes on the tip-most head would be a sensible extension to making
named branches a first class citizen in Mercurial. Currently, named
branches sometimes feel like a late-coming unwanted step-child.
We have run it in a production environment for a while, with fewer
multiple heads occurring in our repositories and fewer confused users as
a result.
Also, it fixes the long-standing issue 736.
Dirkjan and Benoit have furthermore discussed the possibility of
changing the wire protocol to being JSON-based, but for simplicity's
sake, we have not considered this in our patch.
If something like that is desired later on, we could add arguments to
the branchmap wire command, which would return JSON-based information.
Since branch names are currently URL encoded, which includes encoding
the { character, such information can be easily distinguished from
old-style branchmap information, allowing backwards compatibility to be
maintained.
diff --git a/mercurial/hgweb/protocol.py b/mercurial/hgweb/protocol.py
--- a/mercurial/hgweb/protocol.py
+++ b/mercurial/hgweb/protocol.py
@@ -5,7 +5,7 @@
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2, incorporated herein by reference.
-import cStringIO, zlib, tempfile, errno, os, sys
+import cStringIO, zlib, tempfile, errno, os, sys, urllib
from mercurial import util, streamclone
from mercurial.node import bin, hex
from mercurial import changegroup as changegroupmod
@@ -17,6 +17,7 @@
__all__ = [
'lookup', 'heads', 'branches', 'between', 'changegroup',
'changegroupsubset', 'capabilities', 'unbundle', 'stream_out',
+ 'branchmap',
]
HGTYPE = 'application/mercurial-0.1'
@@ -37,6 +38,14 @@
req.respond(HTTP_OK, HGTYPE, length=len(resp))
yield resp
+def branchmap(repo, req):
+ branches = repo.branchmap()
+ heads = ['%s %s' % (urllib.quote(b), " ".join([hex(x) for x in branches[b]])) \
+ for b in branches]
+ resp = "\n".join(heads)
+ req.respond(HTTP_OK, HGTYPE, length=len(resp))
+ yield resp
+
def branches(repo, req):
nodes = []
if 'nodes' in req.form:
@@ -97,7 +106,7 @@
yield z.flush()
def capabilities(repo, req):
- caps = ['lookup', 'changegroupsubset']
+ caps = ['lookup', 'changegroupsubset', 'branchmap']
if repo.ui.configbool('server', 'uncompressed', untrusted=True):
caps.append('stream=%d' % repo.changelog.version)
if changegroupmod.bundlepriority:
diff --git a/mercurial/httprepo.py b/mercurial/httprepo.py
--- a/mercurial/httprepo.py
+++ b/mercurial/httprepo.py
@@ -145,6 +145,19 @@
except:
raise error.ResponseError(_("unexpected response:"), d)
+ def branchmap(self):
+ d = self.do_read("branchmap")
+ try:
+ branchmap = {}
+ for branchpart in d.splitlines():
+ branchheads = branchpart.split(' ')
+ branchname = urllib.unquote(branchheads[0])
+ branchheads = [bin(x) for x in branchheads[1:]]
+ branchmap[branchname] = branchheads
+ return branchmap
+ except:
+ raise error.ResponseError(_("unexpected response:"), d)
+
def branches(self, nodes):
n = " ".join(map(hex, nodes))
d = self.do_read("branches", nodes=n)
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -18,7 +18,7 @@
propertycache = util.propertycache
class localrepository(repo.repository):
- capabilities = set(('lookup', 'changegroupsubset'))
+ capabilities = set(('lookup', 'changegroupsubset', 'branchmap'))
supported = set('revlogv1 store fncache'.split())
def __init__(self, baseui, path=None, create=0):
@@ -360,6 +360,9 @@
return partial
+ def branchmap(self):
+ return self._branchheads()
+
def _branchheads(self):
tip = self.changelog.tip()
if self.branchcache is not None and self._branchcachetip == tip:
diff --git a/mercurial/sshrepo.py b/mercurial/sshrepo.py
--- a/mercurial/sshrepo.py
+++ b/mercurial/sshrepo.py
@@ -8,7 +8,7 @@
from node import bin, hex
from i18n import _
import repo, util, error
-import re
+import urllib, re
class remotelock(object):
def __init__(self, repo):
@@ -166,6 +166,19 @@
except:
self.abort(error.ResponseError(_("unexpected response:"), d))
+ def branchmap(self):
+ d = self.call("branchmap")
+ try:
+ branchmap = {}
+ for branchpart in d.splitlines():
+ branchheads = branchpart.split(' ')
+ branchname = urllib.unquote(branchheads[0])
+ branchheads = [bin(x) for x in branchheads[1:]]
+ branchmap[branchname] = branchheads
+ return branchmap
+ except:
+ raise error.ResponseError(_("unexpected response:"), d)
+
def branches(self, nodes):
n = " ".join(map(hex, nodes))
d = self.call("branches", nodes=n)
diff --git a/mercurial/sshserver.py b/mercurial/sshserver.py
--- a/mercurial/sshserver.py
+++ b/mercurial/sshserver.py
@@ -9,7 +9,7 @@
from i18n import _
from node import bin, hex
import streamclone, util, hook
-import os, sys, tempfile
+import os, sys, tempfile, urllib
class sshserver(object):
def __init__(self, ui, repo):
@@ -64,6 +64,11 @@
success = 0
self.respond("%s %s\n" % (success, r))
+ def do_branchmap(self):
+ h = self.repo.branchmap()
+ hs = ['%s %s' % (urllib.quote(b), " ".join([hex(x) for x in h[b]])) for b in h]
+ self.respond("\n".join(hs))
+
def do_heads(self):
h = self.repo.heads()
self.respond(" ".join(map(hex, h)) + "\n")
@@ -77,7 +82,7 @@
capabilities: space separated list of tokens
'''
- caps = ['unbundle', 'lookup', 'changegroupsubset']
+ caps = ['unbundle', 'lookup', 'changegroupsubset', 'branchmap']
if self.ui.configbool('server', 'uncompressed'):
caps.append('stream=%d' % self.repo.changelog.version)
self.respond("capabilities: %s\n" % (' '.join(caps),))
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