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setdiscovery: make progress on most connected groups each roundtrip...
setdiscovery: make progress on most connected groups each roundtrip Consider history like this: o | o | | | o | | | o |/ o | o | | | o | | | o |/ o | o | | | o | | | o |/ o ~ Assume the left mainline is available in the remote repo and the other commits are only in the local repo. Also imagine that instead of 3 local branches with 3 commits on each, there are 1000 branches (the number of commits on each doesn't matter much here). In such a scenario, the current setdiscovery code will pick a sample size of 200 among these branches and ask the remote which of them it has. However, the discovery for each such branch is completely independent of the discovery for the others -- knowing whether the remote has a commit in one branch doesn't give us any information about the other branches. The discovery will therefore take at least 5 roundtrips (maybe more depending on which commit in each linear chain was sampled). Since the discovery for each branch is independent, there is no reason to let one branch wait for another, so this patch makes it so we sample at least as many commits as there are branches. It may still happen (it's very likely, even) that we get multiple samples from one branch and none from another, but that will even out over a few rounds and I think this is still a big improvement. Because of http header size limits, we still use the old behavior unless experimental.httppostargs=true. I've timed this by running `hg debugdiscovery mozilla-unified --debug` in the mozilla-try repo. Both repos were local. Before this patch, last part of the output was: 2249 total queries in 5276.4859s elapsed time: 5276.652634 seconds heads summary: total common heads: 13 also local heads: 4 also remote heads: 8 both: 4 local heads: 28317 common: 4 missing: 28313 remote heads: 12 common: 8 unknown: 4 local changesets: 2014901 common: 530373 missing: 1484528 common heads: 1dad417c28ad 4a108e94d3e2 4d7ef530fffb 5350524bb654 777e60ca8853 7d97fafba271 9cd2ab4d0029 a55ce37217da d38398e5144e dcc6d7a0dc00 e09297892ada e24ec6070d7b fd559328eaf3 After this patch, the output was (including all the samples, since there were so few now): taking initial sample query 2; still undecided: 1599476, sample size is: 108195 sampling from both directions query 3; still undecided: 810922, sample size is: 194158 sampling from both directions query 4; still undecided: 325882, sample size is: 137302 sampling from both directions query 5; still undecided: 111459, sample size is: 74586 sampling from both directions query 6; still undecided: 26805, sample size is: 23960 sampling from both directions query 7; still undecided: 2549, sample size is: 2528 sampling from both directions query 8; still undecided: 21, sample size is: 21 8 total queries in 24.5064s elapsed time: 24.670051 seconds heads summary: total common heads: 13 also local heads: 4 also remote heads: 8 both: 4 local heads: 28317 common: 4 missing: 28313 remote heads: 12 common: 8 unknown: 4 local changesets: 2014901 common: 530373 missing: 1484528 common heads: 1dad417c28ad 4a108e94d3e2 4d7ef530fffb 5350524bb654 777e60ca8853 7d97fafba271 9cd2ab4d0029 a55ce37217da d38398e5144e dcc6d7a0dc00 e09297892ada e24ec6070d7b fd559328eaf3 Differential Revision: https://phab.mercurial-scm.org/D2647

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subrepos.txt
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Subrepositories let you nest external repositories or projects into a
parent Mercurial repository, and make commands operate on them as a
group.
Mercurial currently supports Mercurial, Git, and Subversion
subrepositories.
Subrepositories are made of three components:
1. Nested repository checkouts. They can appear anywhere in the
parent working directory.
2. Nested repository references. They are defined in ``.hgsub``, which
should be placed in the root of working directory, and
tell where the subrepository checkouts come from. Mercurial
subrepositories are referenced like::
path/to/nested = https://example.com/nested/repo/path
Git and Subversion subrepos are also supported::
path/to/nested = [git]git://example.com/nested/repo/path
path/to/nested = [svn]https://example.com/nested/trunk/path
where ``path/to/nested`` is the checkout location relatively to the
parent Mercurial root, and ``https://example.com/nested/repo/path``
is the source repository path. The source can also reference a
filesystem path.
Note that ``.hgsub`` does not exist by default in Mercurial
repositories, you have to create and add it to the parent
repository before using subrepositories.
3. Nested repository states. They are defined in ``.hgsubstate``, which
is placed in the root of working directory, and
capture whatever information is required to restore the
subrepositories to the state they were committed in a parent
repository changeset. Mercurial automatically record the nested
repositories states when committing in the parent repository.
.. note::
The ``.hgsubstate`` file should not be edited manually.
Adding a Subrepository
======================
If ``.hgsub`` does not exist, create it and add it to the parent
repository. Clone or checkout the external projects where you want it
to live in the parent repository. Edit ``.hgsub`` and add the
subrepository entry as described above. At this point, the
subrepository is tracked and the next commit will record its state in
``.hgsubstate`` and bind it to the committed changeset.
Synchronizing a Subrepository
=============================
Subrepos do not automatically track the latest changeset of their
sources. Instead, they are updated to the changeset that corresponds
with the changeset checked out in the top-level changeset. This is so
developers always get a consistent set of compatible code and
libraries when they update.
Thus, updating subrepos is a manual process. Simply check out target
subrepo at the desired revision, test in the top-level repo, then
commit in the parent repository to record the new combination.
Deleting a Subrepository
========================
To remove a subrepository from the parent repository, delete its
reference from ``.hgsub``, then remove its files.
Interaction with Mercurial Commands
===================================
:add: add does not recurse in subrepos unless -S/--subrepos is
specified. However, if you specify the full path of a file in a
subrepo, it will be added even without -S/--subrepos specified.
Subversion subrepositories are currently silently
ignored.
:addremove: addremove does not recurse into subrepos unless
-S/--subrepos is specified. However, if you specify the full
path of a directory in a subrepo, addremove will be performed on
it even without -S/--subrepos being specified. Git and
Subversion subrepositories will print a warning and continue.
:archive: archive does not recurse in subrepositories unless
-S/--subrepos is specified.
:cat: Git subrepositories only support exact file matches.
Subversion subrepositories are currently ignored.
:commit: commit creates a consistent snapshot of the state of the
entire project and its subrepositories. If any subrepositories
have been modified, Mercurial will abort. Mercurial can be made
to instead commit all modified subrepositories by specifying
-S/--subrepos, or setting "ui.commitsubrepos=True" in a
configuration file (see :hg:`help config`). After there are no
longer any modified subrepositories, it records their state and
finally commits it in the parent repository. The --addremove
option also honors the -S/--subrepos option. However, Git and
Subversion subrepositories will print a warning and abort.
:diff: diff does not recurse in subrepos unless -S/--subrepos is
specified. However, if you specify the full path of a file or
directory in a subrepo, it will be diffed even without
-S/--subrepos being specified. Subversion subrepositories are
currently silently ignored.
:files: files does not recurse into subrepos unless -S/--subrepos is
specified. However, if you specify the full path of a file or
directory in a subrepo, it will be displayed even without
-S/--subrepos being specified. Git and Subversion subrepositories
are currently silently ignored.
:forget: forget currently only handles exact file matches in subrepos.
Git and Subversion subrepositories are currently silently ignored.
:incoming: incoming does not recurse in subrepos unless -S/--subrepos
is specified. Git and Subversion subrepositories are currently
silently ignored.
:outgoing: outgoing does not recurse in subrepos unless -S/--subrepos
is specified. Git and Subversion subrepositories are currently
silently ignored.
:pull: pull is not recursive since it is not clear what to pull prior
to running :hg:`update`. Listing and retrieving all
subrepositories changes referenced by the parent repository pulled
changesets is expensive at best, impossible in the Subversion
case.
:push: Mercurial will automatically push all subrepositories first
when the parent repository is being pushed. This ensures new
subrepository changes are available when referenced by top-level
repositories. Push is a no-op for Subversion subrepositories.
:serve: serve does not recurse into subrepositories unless
-S/--subrepos is specified. Git and Subversion subrepositories
are currently silently ignored.
:status: status does not recurse into subrepositories unless
-S/--subrepos is specified. Subrepository changes are displayed as
regular Mercurial changes on the subrepository
elements. Subversion subrepositories are currently silently
ignored.
:remove: remove does not recurse into subrepositories unless
-S/--subrepos is specified. However, if you specify a file or
directory path in a subrepo, it will be removed even without
-S/--subrepos. Git and Subversion subrepositories are currently
silently ignored.
:update: update restores the subrepos in the state they were
originally committed in target changeset. If the recorded
changeset is not available in the current subrepository, Mercurial
will pull it in first before updating. This means that updating
can require network access when using subrepositories.
Remapping Subrepositories Sources
=================================
A subrepository source location may change during a project life,
invalidating references stored in the parent repository history. To
fix this, rewriting rules can be defined in parent repository ``hgrc``
file or in Mercurial configuration. See the ``[subpaths]`` section in
hgrc(5) for more details.