tests/test-bundle.out

named branches: server branchmap wire protocol support (issue736)

The repository command, 'branchmap', returns a dictionary, branchname
-> [branchheads], and will be 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 patches accomplish.


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.

Co-contributor: Sune Foldager <[e-mail]>

====== Setting up test
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
created new head
1 files updated, 0 files merged, 2 files removed, 0 files unresolved
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
4 files, 9 changesets, 7 total revisions
====== Bundle --all
9 changesets found
====== Bundle test to full.hg
searching for changes
9 changesets found
====== Unbundle full.hg in test
adding changesets
adding manifests
adding file changes
added 0 changesets with 0 changes to 4 files
(run 'hg update' to get a working copy)
====== Verify empty
changeset:   -1:000000000000
tag:         tip
user:        
date:        Thu Jan 01 00:00:00 1970 +0000

checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
0 files, 0 changesets, 0 total revisions
====== Pull full.hg into test (using --cwd)
pulling from ../full.hg
searching for changes
no changes found
====== Pull full.hg into empty (using --cwd)
pulling from ../full.hg
requesting all changes
adding changesets
adding manifests
adding file changes
added 9 changesets with 7 changes to 4 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
====== Rollback empty
rolling back last transaction
====== Pull full.hg into empty again (using --cwd)
pulling from ../full.hg
requesting all changes
adding changesets
adding manifests
adding file changes
added 9 changesets with 7 changes to 4 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
====== Pull full.hg into test (using -R)
pulling from full.hg
searching for changes
no changes found
====== Pull full.hg into empty (using -R)
pulling from full.hg
searching for changes
no changes found
====== Rollback empty
rolling back last transaction
====== Pull full.hg into empty again (using -R)
pulling from full.hg
requesting all changes
adding changesets
adding manifests
adding file changes
added 9 changesets with 7 changes to 4 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
====== Log -R full.hg in fresh empty
changeset:   8:836ac62537ab
tag:         tip
parent:      3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3m

changeset:   7:80fe151401c2
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3m

changeset:   6:1e3f6b843bd6
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3

changeset:   5:024e4e7df376
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.2

changeset:   4:5f4f3ceb285e
parent:      0:5649c9d34dd8
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.1

changeset:   3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3

changeset:   2:d62976ca1e50
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.2

changeset:   1:10b2180f755b
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.1

changeset:   0:5649c9d34dd8
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.0

====== Pull ../full.hg into empty (with hook)
changegroup hook: HG_NODE=5649c9d34dd87d0ecb5fd39672128376e83b22e1 HG_SOURCE=pull HG_URL=bundle:../full.hg 
pulling from bundle://../full.hg
requesting all changes
adding changesets
adding manifests
adding file changes
added 9 changesets with 7 changes to 4 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
====== Rollback empty
rolling back last transaction
====== Log -R bundle:empty+full.hg
8 7 6 5 4 3 2 1 0 
====== Pull full.hg into empty again (using -R; with hook)
changegroup hook: HG_NODE=5649c9d34dd87d0ecb5fd39672128376e83b22e1 HG_SOURCE=pull HG_URL=bundle:empty+full.hg 
pulling from full.hg
requesting all changes
adding changesets
adding manifests
adding file changes
added 9 changesets with 7 changes to 4 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
====== Create partial clones
requesting all changes
adding changesets
adding manifests
adding file changes
added 4 changesets with 4 changes to 1 files
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
====== Log -R full.hg in partial
changeset:   8:836ac62537ab
tag:         tip
parent:      3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3m

changeset:   7:80fe151401c2
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3m

changeset:   6:1e3f6b843bd6
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3

changeset:   5:024e4e7df376
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.2

changeset:   4:5f4f3ceb285e
parent:      0:5649c9d34dd8
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.1

changeset:   3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3

changeset:   2:d62976ca1e50
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.2

changeset:   1:10b2180f755b
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.1

changeset:   0:5649c9d34dd8
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.0

====== Incoming full.hg in partial
comparing with bundle://../full.hg
searching for changes
changeset:   4:5f4f3ceb285e
parent:      0:5649c9d34dd8
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.1

changeset:   5:024e4e7df376
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.2

changeset:   6:1e3f6b843bd6
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3

changeset:   7:80fe151401c2
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3m

changeset:   8:836ac62537ab
tag:         tip
parent:      3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3m

====== Outgoing -R full.hg vs partial2 in partial
comparing with ../partial2
searching for changes
changeset:   4:5f4f3ceb285e
parent:      0:5649c9d34dd8
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.1

changeset:   5:024e4e7df376
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.2

changeset:   6:1e3f6b843bd6
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3

changeset:   7:80fe151401c2
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3m

changeset:   8:836ac62537ab
tag:         tip
parent:      3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3m

====== Outgoing -R does-not-exist.hg vs partial2 in partial
abort: No such file or directory: ../does-not-exist.hg
====== Direct clone from bundle (all-history)
requesting all changes
adding changesets
adding manifests
adding file changes
added 9 changesets with 7 changes to 4 files (+1 heads)
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
changeset:   8:836ac62537ab
tag:         tip
parent:      3:ac69c658229d
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     0.3m

changeset:   7:80fe151401c2
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     1.3m

====== Unbundle incremental bundles into fresh empty in one go
1 changesets found
1 changesets found
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
====== test for 540d1059c802
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
searching for changes
1 changesets found
comparing with ../bundle.hg
searching for changes
changeset:   2:ed1b79f46b9a
tag:         tip
parent:      0:bbd179dfa0a7
user:        test
date:        Thu Jan 01 00:00:00 1970 +0000
summary:     change foo

===== test that verify bundle does not traceback
abort: 00changelog.i@bbd179dfa0a7: unknown parent!
abort: cannot verify bundle or remote repos
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
2 files, 2 changesets, 2 total revisions
====== diff against bundle
diff -r 836ac62537ab anotherfile
--- a/anotherfile	Mon Jan 12 13:46:40 1970 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,4 +0,0 @@
-0
-1
-2
-3