view tests/test-merge-force.t @ 26623:5a95fe44121d

clonebundles: support for seeding clones from pre-generated bundles

Cloning can be an expensive operation for servers because the server
generates a bundle from existing repository data at request time. For
a large repository like mozilla-central, this consumes 4+ minutes
of CPU time on the server. It also results in significant network
utilization. Multiplied by hundreds or even thousands of clients and
the ensuing load can result in difficulties scaling the Mercurial server.

Despite generation of bundles being deterministic until the next
changeset is added, the generation of bundles to service a clone request
is not cached. Each clone thus performs redundant work. This is
wasteful.

This patch introduces the "clonebundles" extension and related
client-side functionality to help alleviate this deficiency. The
client-side feature is behind an experimental flag and is not enabled by
default.

It works as follows:

1) Server operator generates a bundle and makes it available on a
   server (likely HTTP).
2) Server operator defines the URL of a bundle file in a
   .hg/clonebundles.manifest file.
3) Client `hg clone`ing sees the server is advertising bundle URLs.
4) Client fetches and applies the advertised bundle.
5) Client performs equivalent of `hg pull` to fetch changes made since
   the bundle was created.

Essentially, the server performs the expensive work of generating a
bundle once and all subsequent clones fetch a static file from
somewhere. Scaling static file serving is a much more manageable
problem than scaling a Python application like Mercurial. Assuming your
repository grows less than 1% per day, the end result is 99+% of CPU
and network load from clones is eliminated, allowing Mercurial servers
to scale more easily. Serving static files also means data can be
transferred to clients as fast as they can consume it, rather than as
fast as servers can generate it. This makes clones faster.

Mozilla has implemented similar functionality of this patch on
hg.mozilla.org using a custom extension. We are hosting bundle files in
Amazon S3 and CloudFront (a CDN) and have successfully offloaded
>1 TB/day in data transfer from hg.mozilla.org, freeing up significant
bandwidth and CPU resources. The positive impact has been stellar and
I believe it has proved its value to be included in Mercurial core. I
feel it is important for the client-side support to be enabled in core
by default because it means that clients will get faster, more reliable
clones and will enable server operators to reduce load without
requiring any client-side configuration changes (assuming clients are
up to date, of course).

The scope of this feature is narrowly and specifically tailored to
cloning, despite "serve pulls from pre-generated bundles" being a valid
and useful feature. I would eventually like for Mercurial servers to
support transferring *all* repository data via statically hosted files.
You could imagine a server that siphons all pushed data to bundle files
and instructs clients to apply a stream of bundles to reconstruct all
repository data. This feature, while useful and powerful, is
significantly more work to implement because it requires the server
component have awareness of discovery and a mapping of which changesets
are in which files. Full, clone bundles, by contrast, are much simpler.

The wire protocol command is named "clonebundles" instead of something
more generic like "staticbundles" to leave the door open for a new, more
powerful and more generic server-side component with minimal backwards
compatibility implications. The name "bundleclone" is used by Mozilla's
extension and would cause problems since there are subtle differences
in Mozilla's extension.

Mozilla's experience with this idea has taught us that some form of
"content negotiation" is required. Not all clients will support all
bundle formats or even URLs (advanced TLS requirements, etc). To ensure
the highest uptake possible, a server needs to advertise multiple
versions of bundles and clients need to be able to choose the most
appropriate from that list one. The "attributes" in each
server-advertised entry facilitate this filtering and sorting. Their
use will become apparent in subsequent patches.

Initial inspiration and credit for the idea of cloning from static files
belongs to Augie Fackler and his "lookaside clone" extension proof of
concept.

Set up a base, local, and remote changeset, as well as the working copy state.
Files names are of the form base_remote_local_working-copy. For example,
content1_content2_content1_content2-untracked represents a
file that was modified in the remote changeset, left untouched in the
local changeset, and then modified in the working copy to match the
remote content, then finally forgotten.

  $ hg init

Create base changeset

  $ python $TESTDIR/generate-working-copy-states.py state 3 1
  $ hg addremove -q --similarity 0
  $ hg commit -qm 'base'

Create remote changeset

  $ python $TESTDIR/generate-working-copy-states.py state 3 2
  $ hg addremove -q --similarity 0
  $ hg commit -qm 'remote'

Create local changeset

  $ hg update -q 0
  $ python $TESTDIR/generate-working-copy-states.py state 3 3
  $ hg addremove -q --similarity 0
  $ hg commit -qm 'local'

Set up working directory

  $ python $TESTDIR/generate-working-copy-states.py state 3 wc
  $ hg addremove -q --similarity 0
  $ hg forget *_*_*_*-untracked
  $ rm *_*_*_missing-*

  $ hg status -A
  M content1_content1_content1_content4-tracked
  M content1_content1_content3_content1-tracked
  M content1_content1_content3_content4-tracked
  M content1_content2_content1_content2-tracked
  M content1_content2_content1_content4-tracked
  M content1_content2_content2_content1-tracked
  M content1_content2_content2_content4-tracked
  M content1_content2_content3_content1-tracked
  M content1_content2_content3_content2-tracked
  M content1_content2_content3_content4-tracked
  M content1_missing_content1_content4-tracked
  M content1_missing_content3_content1-tracked
  M content1_missing_content3_content4-tracked
  M missing_content2_content2_content4-tracked
  M missing_content2_content3_content2-tracked
  M missing_content2_content3_content4-tracked
  M missing_missing_content3_content4-tracked
  A content1_content1_missing_content1-tracked
  A content1_content1_missing_content4-tracked
  A content1_content2_missing_content1-tracked
  A content1_content2_missing_content2-tracked
  A content1_content2_missing_content4-tracked
  A content1_missing_missing_content1-tracked
  A content1_missing_missing_content4-tracked
  A missing_content2_missing_content2-tracked
  A missing_content2_missing_content4-tracked
  A missing_missing_missing_content4-tracked
  R content1_content1_content1_content1-untracked
  R content1_content1_content1_content4-untracked
  R content1_content1_content1_missing-untracked
  R content1_content1_content3_content1-untracked
  R content1_content1_content3_content3-untracked
  R content1_content1_content3_content4-untracked
  R content1_content1_content3_missing-untracked
  R content1_content2_content1_content1-untracked
  R content1_content2_content1_content2-untracked
  R content1_content2_content1_content4-untracked
  R content1_content2_content1_missing-untracked
  R content1_content2_content2_content1-untracked
  R content1_content2_content2_content2-untracked
  R content1_content2_content2_content4-untracked
  R content1_content2_content2_missing-untracked
  R content1_content2_content3_content1-untracked
  R content1_content2_content3_content2-untracked
  R content1_content2_content3_content3-untracked
  R content1_content2_content3_content4-untracked
  R content1_content2_content3_missing-untracked
  R content1_missing_content1_content1-untracked
  R content1_missing_content1_content4-untracked
  R content1_missing_content1_missing-untracked
  R content1_missing_content3_content1-untracked
  R content1_missing_content3_content3-untracked
  R content1_missing_content3_content4-untracked
  R content1_missing_content3_missing-untracked
  R missing_content2_content2_content2-untracked
  R missing_content2_content2_content4-untracked
  R missing_content2_content2_missing-untracked
  R missing_content2_content3_content2-untracked
  R missing_content2_content3_content3-untracked
  R missing_content2_content3_content4-untracked
  R missing_content2_content3_missing-untracked
  R missing_missing_content3_content3-untracked
  R missing_missing_content3_content4-untracked
  R missing_missing_content3_missing-untracked
  ! content1_content1_content1_missing-tracked
  ! content1_content1_content3_missing-tracked
  ! content1_content1_missing_missing-tracked
  ! content1_content2_content1_missing-tracked
  ! content1_content2_content2_missing-tracked
  ! content1_content2_content3_missing-tracked
  ! content1_content2_missing_missing-tracked
  ! content1_missing_content1_missing-tracked
  ! content1_missing_content3_missing-tracked
  ! content1_missing_missing_missing-tracked
  ! missing_content2_content2_missing-tracked
  ! missing_content2_content3_missing-tracked
  ! missing_content2_missing_missing-tracked
  ! missing_missing_content3_missing-tracked
  ! missing_missing_missing_missing-tracked
  ? content1_content1_missing_content1-untracked
  ? content1_content1_missing_content4-untracked
  ? content1_content2_missing_content1-untracked
  ? content1_content2_missing_content2-untracked
  ? content1_content2_missing_content4-untracked
  ? content1_missing_missing_content1-untracked
  ? content1_missing_missing_content4-untracked
  ? missing_content2_missing_content2-untracked
  ? missing_content2_missing_content4-untracked
  ? missing_missing_missing_content4-untracked
  C content1_content1_content1_content1-tracked
  C content1_content1_content3_content3-tracked
  C content1_content2_content1_content1-tracked
  C content1_content2_content2_content2-tracked
  C content1_content2_content3_content3-tracked
  C content1_missing_content1_content1-tracked
  C content1_missing_content3_content3-tracked
  C missing_content2_content2_content2-tracked
  C missing_content2_content3_content3-tracked
  C missing_missing_content3_content3-tracked

Merge with remote

# Notes:
# - local and remote changed content1_content2_*_content2-untracked
#   in the same way, so it could potentially be left alone

  $ hg merge -f --tool internal:merge3 'desc("remote")'
  local changed content1_missing_content1_content4-tracked which remote deleted
  use (c)hanged version or (d)elete? c
  local changed content1_missing_content3_content3-tracked which remote deleted
  use (c)hanged version or (d)elete? c
  local changed content1_missing_content3_content4-tracked which remote deleted
  use (c)hanged version or (d)elete? c
  local changed content1_missing_missing_content4-tracked which remote deleted
  use (c)hanged version or (d)elete? c
  remote changed content1_content2_content1_content1-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content1_content2-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content1_content4-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content1_missing-tracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content1_missing-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content2_content1-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content2_content2-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content2_content4-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content2_missing-tracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content2_missing-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content3_content1-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content3_content2-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content3_content3-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content3_content4-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content3_missing-tracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_content3_missing-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_missing_content1-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_missing_content2-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_missing_content4-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_missing_missing-tracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  remote changed content1_content2_missing_missing-untracked which local deleted
  use (c)hanged version or leave (d)eleted? c
  merging content1_content2_content1_content4-tracked
  merging content1_content2_content2_content1-tracked
  merging content1_content2_content2_content4-tracked
  merging content1_content2_content3_content1-tracked
  merging content1_content2_content3_content3-tracked
  merging content1_content2_content3_content4-tracked
  merging content1_content2_missing_content1-tracked
  merging content1_content2_missing_content4-tracked
  merging missing_content2_content2_content4-tracked
  merging missing_content2_content3_content3-tracked
  merging missing_content2_content3_content4-tracked
  merging missing_content2_missing_content4-tracked
  merging missing_content2_missing_content4-untracked
  warning: conflicts while merging content1_content2_content1_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging content1_content2_content2_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging content1_content2_content3_content3-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging content1_content2_content3_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging content1_content2_missing_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging missing_content2_content2_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging missing_content2_content3_content3-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging missing_content2_content3_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging missing_content2_missing_content4-tracked! (edit, then use 'hg resolve --mark')
  warning: conflicts while merging missing_content2_missing_content4-untracked! (edit, then use 'hg resolve --mark')
  39 files updated, 3 files merged, 8 files removed, 10 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
  [1]

Check which files need to be resolved (should correspond to the output above).
This should be the files for which the base (1st filename segment), the remote
(2nd segment) and the working copy (4th segment) are all different.

Interestingly, one untracked file got merged and added, which corresponds to the
odd 'if force and branchmerge and different' case in manifestmerge().

  $ hg resolve -l
  U content1_content2_content1_content4-tracked
  R content1_content2_content2_content1-tracked
  U content1_content2_content2_content4-tracked
  R content1_content2_content3_content1-tracked
  U content1_content2_content3_content3-tracked
  U content1_content2_content3_content4-tracked
  R content1_content2_missing_content1-tracked
  U content1_content2_missing_content4-tracked
  U missing_content2_content2_content4-tracked
  U missing_content2_content3_content3-tracked
  U missing_content2_content3_content4-tracked
  U missing_content2_missing_content4-tracked
  U missing_content2_missing_content4-untracked

Check status and file content

Some files get added (e.g. content1_content2_content1_content1-untracked)

It is not intuitive that content1_content2_content1_content4-tracked gets
merged while content1_content2_content1_content4-untracked gets overwritten.
Any *_content2_*-untracked triggers the modified/deleted prompt and then gets
overwritten.

A lot of untracked files become tracked, for example
content1_content2_content2_content2-untracked.

*_missing_missing_missing-tracked is reported as removed ('R'), which
doesn't make sense since the file did not exist in the parent, but on the
other hand, merged-in additions are reported as modifications, which is
almost as strange.

missing_missing_content3_missing-tracked becomes removed ('R'), even though
the remote side did not touch the file

  $ for f in `python $TESTDIR/generate-working-copy-states.py filelist 3`
  > do
  >   echo
  >   hg status -A $f
  >   if test -f $f
  >   then
  >     cat $f
  >   else
  >     echo '<missing>'
  >   fi
  >   if test -f ${f}.orig
  >   then
  >     echo ${f}.orig:
  >     cat ${f}.orig
  >   fi
  > done
  
  C content1_content1_content1_content1-tracked
  content1
  
  R content1_content1_content1_content1-untracked
  content1
  
  M content1_content1_content1_content4-tracked
  content4
  
  R content1_content1_content1_content4-untracked
  content4
  
  ! content1_content1_content1_missing-tracked
  <missing>
  
  R content1_content1_content1_missing-untracked
  <missing>
  
  M content1_content1_content3_content1-tracked
  content1
  
  R content1_content1_content3_content1-untracked
  content1
  
  C content1_content1_content3_content3-tracked
  content3
  
  R content1_content1_content3_content3-untracked
  content3
  
  M content1_content1_content3_content4-tracked
  content4
  
  R content1_content1_content3_content4-untracked
  content4
  
  ! content1_content1_content3_missing-tracked
  <missing>
  
  R content1_content1_content3_missing-untracked
  <missing>
  
  A content1_content1_missing_content1-tracked
  content1
  
  ? content1_content1_missing_content1-untracked
  content1
  
  A content1_content1_missing_content4-tracked
  content4
  
  ? content1_content1_missing_content4-untracked
  content4
  
  ! content1_content1_missing_missing-tracked
  <missing>
  
  content1_content1_missing_missing-untracked: * (glob)
  <missing>
  
  M content1_content2_content1_content1-tracked
  content2
  
  M content1_content2_content1_content1-untracked
  content2
  
  M content1_content2_content1_content2-tracked
  content2
  
  M content1_content2_content1_content2-untracked
  content2
  
  M content1_content2_content1_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  content1
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  content1_content2_content1_content4-tracked.orig:
  content4
  
  M content1_content2_content1_content4-untracked
  content2
  
  M content1_content2_content1_missing-tracked
  content2
  
  M content1_content2_content1_missing-untracked
  content2
  
  M content1_content2_content2_content1-tracked
  content2
  
  M content1_content2_content2_content1-untracked
  content2
  
  C content1_content2_content2_content2-tracked
  content2
  
  M content1_content2_content2_content2-untracked
  content2
  
  M content1_content2_content2_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  content1
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  content1_content2_content2_content4-tracked.orig:
  content4
  
  M content1_content2_content2_content4-untracked
  content2
  
  M content1_content2_content2_missing-tracked
  content2
  
  M content1_content2_content2_missing-untracked
  content2
  
  M content1_content2_content3_content1-tracked
  content2
  
  M content1_content2_content3_content1-untracked
  content2
  
  M content1_content2_content3_content2-tracked
  content2
  
  M content1_content2_content3_content2-untracked
  content2
  
  M content1_content2_content3_content3-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content3
  ||||||| base
  content1
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  content1_content2_content3_content3-tracked.orig:
  content3
  
  M content1_content2_content3_content3-untracked
  content2
  
  M content1_content2_content3_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  content1
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  content1_content2_content3_content4-tracked.orig:
  content4
  
  M content1_content2_content3_content4-untracked
  content2
  
  M content1_content2_content3_missing-tracked
  content2
  
  M content1_content2_content3_missing-untracked
  content2
  
  M content1_content2_missing_content1-tracked
  content2
  
  M content1_content2_missing_content1-untracked
  content2
  
  M content1_content2_missing_content2-tracked
  content2
  
  M content1_content2_missing_content2-untracked
  content2
  
  M content1_content2_missing_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  content1
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  content1_content2_missing_content4-tracked.orig:
  content4
  
  M content1_content2_missing_content4-untracked
  content2
  
  M content1_content2_missing_missing-tracked
  content2
  
  M content1_content2_missing_missing-untracked
  content2
  
  R content1_missing_content1_content1-tracked
  <missing>
  
  R content1_missing_content1_content1-untracked
  content1
  
  M content1_missing_content1_content4-tracked
  content4
  
  R content1_missing_content1_content4-untracked
  content4
  
  R content1_missing_content1_missing-tracked
  <missing>
  
  R content1_missing_content1_missing-untracked
  <missing>
  
  R content1_missing_content3_content1-tracked
  <missing>
  
  R content1_missing_content3_content1-untracked
  content1
  
  C content1_missing_content3_content3-tracked
  content3
  
  R content1_missing_content3_content3-untracked
  content3
  
  M content1_missing_content3_content4-tracked
  content4
  
  R content1_missing_content3_content4-untracked
  content4
  
  R content1_missing_content3_missing-tracked
  <missing>
  
  R content1_missing_content3_missing-untracked
  <missing>
  
  R content1_missing_missing_content1-tracked
  <missing>
  
  ? content1_missing_missing_content1-untracked
  content1
  
  A content1_missing_missing_content4-tracked
  content4
  
  ? content1_missing_missing_content4-untracked
  content4
  
  R content1_missing_missing_missing-tracked
  <missing>
  
  content1_missing_missing_missing-untracked: * (glob)
  <missing>
  
  C missing_content2_content2_content2-tracked
  content2
  
  M missing_content2_content2_content2-untracked
  content2
  
  M missing_content2_content2_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  missing_content2_content2_content4-tracked.orig:
  content4
  
  M missing_content2_content2_content4-untracked
  content2
  
  M missing_content2_content2_missing-tracked
  content2
  
  M missing_content2_content2_missing-untracked
  content2
  
  M missing_content2_content3_content2-tracked
  content2
  
  M missing_content2_content3_content2-untracked
  content2
  
  M missing_content2_content3_content3-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content3
  ||||||| base
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  missing_content2_content3_content3-tracked.orig:
  content3
  
  M missing_content2_content3_content3-untracked
  content2
  
  M missing_content2_content3_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  missing_content2_content3_content4-tracked.orig:
  content4
  
  M missing_content2_content3_content4-untracked
  content2
  
  M missing_content2_content3_missing-tracked
  content2
  
  M missing_content2_content3_missing-untracked
  content2
  
  M missing_content2_missing_content2-tracked
  content2
  
  M missing_content2_missing_content2-untracked
  content2
  
  M missing_content2_missing_content4-tracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  missing_content2_missing_content4-tracked.orig:
  content4
  
  M missing_content2_missing_content4-untracked
  <<<<<<< local: 0447570f1af6 - test: local
  content4
  ||||||| base
  =======
  content2
  >>>>>>> other: 85100b8c675b  - test: remote
  missing_content2_missing_content4-untracked.orig:
  content4
  
  M missing_content2_missing_missing-tracked
  content2
  
  M missing_content2_missing_missing-untracked
  content2
  
  C missing_missing_content3_content3-tracked
  content3
  
  R missing_missing_content3_content3-untracked
  content3
  
  M missing_missing_content3_content4-tracked
  content4
  
  R missing_missing_content3_content4-untracked
  content4
  
  R missing_missing_content3_missing-tracked
  <missing>
  
  R missing_missing_content3_missing-untracked
  <missing>
  
  A missing_missing_missing_content4-tracked
  content4
  
  ? missing_missing_missing_content4-untracked
  content4
  
  R missing_missing_missing_missing-tracked
  <missing>
  
  missing_missing_missing_missing-untracked: * (glob)
  <missing>