view tests/test-convert-bzr.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.

#require bzr

  $ . "$TESTDIR/bzr-definitions"

create and rename on the same file in the same step

  $ mkdir test-createandrename
  $ cd test-createandrename
  $ bzr init -q source

test empty repo conversion (issue3233)

  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...

back to the rename stuff

  $ cd source
  $ echo a > a
  $ echo c > c
  $ echo e > e
  $ bzr add -q a c e
  $ bzr commit -q -m 'Initial add: a, c, e'
  $ bzr mv a b
  a => b
  $ bzr mv c d
  c => d
  $ bzr mv e f
  e => f
  $ echo a2 >> a
  $ mkdir e
  $ bzr add -q a e
  $ bzr commit -q -m 'rename a into b, create a, rename c into d'
  $ cd ..
  $ hg convert source source-hg
  scanning source...
  sorting...
  converting...
  1 Initial add: a, c, e
  0 rename a into b, create a, rename c into d
  $ glog -R source-hg
  o  1@source "rename a into b, create a, rename c into d" files: a b c d e f
  |
  o  0@source "Initial add: a, c, e" files: a c e
  

manifest

  $ hg manifest -R source-hg -r tip
  a
  b
  d
  f

test --rev option

  $ hg convert -r 1 source source-1-hg
  initializing destination source-1-hg repository
  scanning source...
  sorting...
  converting...
  0 Initial add: a, c, e
  $ glog -R source-1-hg
  o  0@source "Initial add: a, c, e" files: a c e
  

test with filemap

  $ cat > filemap <<EOF
  > exclude a
  > EOF
  $ hg convert --filemap filemap source source-filemap-hg
  initializing destination source-filemap-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial add: a, c, e
  0 rename a into b, create a, rename c into d
  $ hg -R source-filemap-hg manifest -r tip
  b
  d
  f

convert from lightweight checkout

  $ bzr checkout --lightweight source source-light
  $ hg convert -s bzr source-light source-light-hg
  initializing destination source-light-hg repository
  warning: lightweight checkouts may cause conversion failures, try with a regular branch instead.
  $TESTTMP/test-createandrename/source-light does not look like a Bazaar repository
  abort: source-light: missing or unsupported repository
  [255]

extract timestamps that look just like hg's {date|isodate}:
yyyy-mm-dd HH:MM zzzz (no seconds!)
compare timestamps

  $ cd source
  $ bzr log | \
  >   sed '/timestamp/!d;s/.\{15\}\([0-9: -]\{16\}\):.. \(.[0-9]\{4\}\)/\1 \2/' \
  >   > ../bzr-timestamps
  $ cd ..
  $ hg -R source-hg log --template "{date|isodate}\n" > hg-timestamps
  $ cmp bzr-timestamps hg-timestamps || diff -u bzr-timestamps hg-timestamps
  $ cd ..

merge

  $ mkdir test-merge
  $ cd test-merge
  $ cat > helper.py <<EOF
  > import sys
  > from bzrlib import workingtree
  > wt = workingtree.WorkingTree.open('.')
  > 
  > message, stamp = sys.argv[1:]
  > wt.commit(message, timestamp=int(stamp))
  > EOF
  $ bzr init -q source
  $ cd source
  $ echo content > a
  $ echo content2 > b
  $ bzr add -q a b
  $ bzr commit -q -m 'Initial add'
  $ cd ..
  $ bzr branch -q source source-improve
  $ cd source
  $ echo more >> a
  $ python ../helper.py 'Editing a' 100
  $ cd ../source-improve
  $ echo content3 >> b
  $ python ../helper.py 'Editing b' 200
  $ cd ../source
  $ bzr merge -q ../source-improve
  $ bzr commit -q -m 'Merged improve branch'
  $ cd ..
  $ hg convert --datesort source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  3 Initial add
  2 Editing a
  1 Editing b
  0 Merged improve branch
  $ glog -R source-hg
  o    3@source "Merged improve branch" files:
  |\
  | o  2@source-improve "Editing b" files: b
  | |
  o |  1@source "Editing a" files: a
  |/
  o  0@source "Initial add" files: a b
  
  $ cd ..

#if symlink execbit

symlinks and executable files

  $ mkdir test-symlinks
  $ cd test-symlinks
  $ bzr init -q source
  $ cd source
  $ touch program
  $ chmod +x program
  $ ln -s program altname
  $ mkdir d
  $ echo a > d/a
  $ ln -s a syma
  $ bzr add -q altname program syma d/a
  $ bzr commit -q -m 'Initial setup'
  $ touch newprog
  $ chmod +x newprog
  $ rm altname
  $ ln -s newprog altname
  $ chmod -x program
  $ bzr add -q newprog
  $ bzr commit -q -m 'Symlink changed, x bits changed'
  $ cd ..
  $ hg convert source source-hg
  initializing destination source-hg repository
  scanning source...
  sorting...
  converting...
  1 Initial setup
  0 Symlink changed, x bits changed
  $ manifest source-hg 0
  % manifest of 0
  644 @ altname
  644   d/a
  755 * program
  644 @ syma
  $ manifest source-hg tip
  % manifest of tip
  644 @ altname
  644   d/a
  755 * newprog
  644   program
  644 @ syma

test the symlinks can be recreated

  $ cd source-hg
  $ hg up
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg cat syma; echo
  a
  $ cd ../..

#endif

Multiple branches

  $ bzr init-repo -q --no-trees repo
  $ bzr init -q repo/trunk
  $ bzr co repo/trunk repo-trunk
  $ cd repo-trunk
  $ echo a > a
  $ bzr add -q a
  $ bzr ci -qm adda
  $ bzr tag trunk-tag
  Created tag trunk-tag.
  $ bzr switch -b branch
  Tree is up to date at revision 1.
  Switched to branch: *repo/branch/ (glob)
  $ sleep 1
  $ echo b > b
  $ bzr add -q b
  $ bzr ci -qm addb
  $ bzr tag branch-tag
  Created tag branch-tag.
  $ bzr switch --force ../repo/trunk
  Updated to revision 1.
  Switched to branch: */repo/trunk/ (glob)
  $ sleep 1
  $ echo a >> a
  $ bzr ci -qm changea
  $ cd ..
  $ hg convert --datesort repo repo-bzr
  initializing destination repo-bzr repository
  scanning source...
  sorting...
  converting...
  2 adda
  1 addb
  0 changea
  updating tags
  $ (cd repo-bzr; glog)
  o  3@default "update tags" files: .hgtags
  |
  o  2@default "changea" files: a
  |
  | o  1@branch "addb" files: b
  |/
  o  0@default "adda" files: a
  

Test tags (converted identifiers are not stable because bzr ones are
not and get incorporated in extra fields).

  $ hg -R repo-bzr tags
  tip                                3:* (glob)
  branch-tag                         1:* (glob)
  trunk-tag                          0:* (glob)

Nested repositories (issue3254)

  $ bzr init-repo -q --no-trees repo/inner
  $ bzr init -q repo/inner/trunk
  $ bzr co repo/inner/trunk inner-trunk
  $ cd inner-trunk
  $ echo b > b
  $ bzr add -q b
  $ bzr ci -qm addb
  $ cd ..
  $ hg convert --datesort repo noinner-bzr
  initializing destination noinner-bzr repository
  scanning source...
  sorting...
  converting...
  2 adda
  1 addb
  0 changea
  updating tags