view tests/test-convert-hg-sink.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.

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > convert=
  > [convert]
  > hg.saverev=False
  > EOF
  $ hg init orig
  $ cd orig
  $ echo foo > foo
  $ echo bar > bar
  $ hg ci -qAm 'add foo and bar'
  $ hg rm foo
  $ hg ci -m 'remove foo'
  $ mkdir foo
  $ echo file > foo/file
  $ hg ci -qAm 'add foo/file'
  $ hg tag some-tag
  $ hg tag -l local-tag
  $ hg log
  changeset:   3:593cbf6fb2b4
  tag:         local-tag
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag some-tag for changeset ad681a868e44
  
  changeset:   2:ad681a868e44
  tag:         some-tag
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo/file
  
  changeset:   1:cbba8ecc03b7
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     remove foo
  
  changeset:   0:327daa9251fa
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add foo and bar
  
  $ hg phase --public -r tip
  $ cd ..
  $ hg convert orig new 2>&1 | grep -v 'subversion python bindings could not be loaded'
  initializing destination new repository
  scanning source...
  sorting...
  converting...
  3 add foo and bar
  2 remove foo
  1 add foo/file
  0 Added tag some-tag for changeset ad681a868e44
  $ cd new
  $ hg log -G --template '{rev} {node|short} ({phase}) "{desc}"\n'
  o  3 593cbf6fb2b4 (public) "Added tag some-tag for changeset ad681a868e44"
  |
  o  2 ad681a868e44 (public) "add foo/file"
  |
  o  1 cbba8ecc03b7 (public) "remove foo"
  |
  o  0 327daa9251fa (public) "add foo and bar"
  

  $ hg out ../orig
  comparing with ../orig
  searching for changes
  no changes found
  [1]

dirstate should be empty:

  $ hg debugstate
  $ hg parents -q
  $ hg up -C
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg copy bar baz

put something in the dirstate:

  $ hg debugstate > debugstate
  $ grep baz debugstate
  a   0         -1 unset               baz
  copy: bar -> baz

add a new revision in the original repo

  $ cd ../orig
  $ echo baz > baz
  $ hg ci -qAm 'add baz'
  $ cd ..
  $ hg convert orig new 2>&1 | grep -v 'subversion python bindings could not be loaded'
  scanning source...
  sorting...
  converting...
  0 add baz
  $ cd new
  $ hg out ../orig
  comparing with ../orig
  searching for changes
  no changes found
  [1]

dirstate should be the same (no output below):

  $ hg debugstate > new-debugstate
  $ diff debugstate new-debugstate

no copies

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg debugrename baz
  baz not renamed
  $ cd ..

test tag rewriting

  $ cat > filemap <<EOF
  > exclude foo
  > EOF
  $ hg convert --filemap filemap orig new-filemap 2>&1 | grep -v 'subversion python bindings could not be loaded'
  initializing destination new-filemap repository
  scanning source...
  sorting...
  converting...
  4 add foo and bar
  3 remove foo
  2 add foo/file
  1 Added tag some-tag for changeset ad681a868e44
  0 add baz
  $ cd new-filemap
  $ hg tags
  tip                                2:3c74706b1ff8
  some-tag                           0:ba8636729451
  $ cd ..


Test cases for hg-hg roundtrip

Helper

  $ glog()
  > {
  >     hg log -G --template '{rev} {node|short} ({phase}) "{desc}" files: {files}\n' $*
  > }

Create a tricky source repo

  $ hg init source
  $ cd source

  $ echo 0 > 0
  $ hg ci -Aqm '0: add 0'
  $ echo a > a
  $ mkdir dir
  $ echo b > dir/b
  $ hg ci -qAm '1: add a and dir/b'
  $ echo c > dir/c
  $ hg ci -qAm '2: add dir/c'
  $ hg copy a e
  $ echo b >> b
  $ hg ci -qAm '3: copy a to e, change b'
  $ hg up -qr -3
  $ echo a >> a
  $ hg ci -qAm '4: change a'
  $ hg merge
  merging a and e to e
  2 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg copy b dir/d
  $ hg ci -qAm '5: merge 2 and 3, copy b to dir/d'
  $ echo a >> a
  $ hg ci -qAm '6: change a'

  $ hg mani
  0
  a
  b
  dir/b
  dir/c
  dir/d
  e
  $ hg phase --public -r tip
  $ glog
  @  6 0613c8e59a3d (public) "6: change a" files: a
  |
  o    5 717e9b37cdb7 (public) "5: merge 2 and 3, copy b to dir/d" files: dir/d e
  |\
  | o  4 86a55cb968d5 (public) "4: change a" files: a
  | |
  o |  3 0e6e235919dd (public) "3: copy a to e, change b" files: b e
  | |
  o |  2 0394b0d5e4f7 (public) "2: add dir/c" files: dir/c
  |/
  o  1 333546584845 (public) "1: add a and dir/b" files: a dir/b
  |
  o  0 d1a24e2ebd23 (public) "0: add 0" files: 0
  
  $ cd ..

Convert excluding rev 0 and dir/ (and thus rev2):

  $ cat << EOF > filemap
  > exclude dir
  > EOF

  $ hg convert --filemap filemap source dest --config convert.hg.revs=1::
  initializing destination dest repository
  scanning source...
  sorting...
  converting...
  5 1: add a and dir/b
  4 2: add dir/c
  3 3: copy a to e, change b
  2 4: change a
  1 5: merge 2 and 3, copy b to dir/d
  0 6: change a

Verify that conversion skipped rev 2:

  $ glog -R dest
  o  4 78814e84a217 (draft) "6: change a" files: a
  |
  o    3 f7cff662c5e5 (draft) "5: merge 2 and 3, copy b to dir/d" files: e
  |\
  | o  2 ab40a95b0072 (draft) "4: change a" files: a
  | |
  o |  1 bd51f17597bf (draft) "3: copy a to e, change b" files: b e
  |/
  o  0 a4a1dae0fe35 (draft) "1: add a and dir/b" files: 0 a
  

Verify mapping correct in both directions:

  $ cat source/.hg/shamap
  a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5 333546584845f70c4cfecb992341aaef0e708166
  bd51f17597bf32268e68a560b206898c3960cda2 0e6e235919dd8e9285ba8eb5adf703af9ad99378
  ab40a95b00725307e79c2fd271000aa8af9759f4 86a55cb968d51770cba2a1630d6cc637b574580a
  f7cff662c5e581e6f3f1a85ffdd2bcb35825f6ba 717e9b37cdb7eb9917ca8e30aa3f986e6d5b177d
  78814e84a217894517c2de392b903ed05e6871a4 0613c8e59a3ddb9789072ef52f1ed13496489bb4
  $ cat dest/.hg/shamap
  333546584845f70c4cfecb992341aaef0e708166 a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5
  0394b0d5e4f761ced559fd0bbdc6afc16cb3f7d1 a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5
  0e6e235919dd8e9285ba8eb5adf703af9ad99378 bd51f17597bf32268e68a560b206898c3960cda2
  86a55cb968d51770cba2a1630d6cc637b574580a ab40a95b00725307e79c2fd271000aa8af9759f4
  717e9b37cdb7eb9917ca8e30aa3f986e6d5b177d f7cff662c5e581e6f3f1a85ffdd2bcb35825f6ba
  0613c8e59a3ddb9789072ef52f1ed13496489bb4 78814e84a217894517c2de392b903ed05e6871a4

Verify meta data converted correctly:

  $ hg -R dest log -r 1 --debug -p --git
  changeset:   1:bd51f17597bf32268e68a560b206898c3960cda2
  phase:       draft
  parent:      0:a4a1dae0fe3514cefd9b8541b7abbc8f44f946d5
  parent:      -1:0000000000000000000000000000000000000000
  manifest:    1:040c72ed9b101773c24ac314776bfc846943781f
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files+:      b e
  extra:       branch=default
  description:
  3: copy a to e, change b
  
  
  diff --git a/b b/b
  new file mode 100644
  --- /dev/null
  +++ b/b
  @@ -0,0 +1,1 @@
  +b
  diff --git a/a b/e
  copy from a
  copy to e
  
Verify files included and excluded correctly:

  $ hg -R dest manifest -r tip
  0
  a
  b
  e


Make changes in dest and convert back:

  $ hg -R dest up -q
  $ echo dest > dest/dest
  $ hg -R dest ci -Aqm 'change in dest'
  $ hg -R dest tip
  changeset:   5:a2e0e3cc6d1d
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     change in dest
  

(converting merges back after using a filemap will probably cause chaos so we
exclude merges.)

  $ hg convert dest source --config convert.hg.revs='!merge()'
  scanning source...
  sorting...
  converting...
  0 change in dest

Verify the conversion back:

  $ hg -R source log --debug -r tip
  changeset:   7:e6d364a69ff1248b2099e603b0c145504cade6f0
  tag:         tip
  phase:       draft
  parent:      6:0613c8e59a3ddb9789072ef52f1ed13496489bb4
  parent:      -1:0000000000000000000000000000000000000000
  manifest:    7:aa3e9542f3b76d4f1f1b2e9c7ce9dbb48b6a95ec
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files+:      dest
  extra:       branch=default
  description:
  change in dest
  
  
Files that had been excluded are still present:

  $ hg -R source manifest -r tip
  0
  a
  b
  dest
  dir/b
  dir/c
  dir/d
  e

More source changes

  $ cd source
  $ echo 1 >> a
  $ hg ci -m '8: source first branch'
  created new head
  $ hg up -qr -2
  $ echo 2 >> a
  $ hg ci -m '9: source second branch'
  $ hg merge -q --tool internal:local
  $ hg ci -m '10: source merge'
  $ echo >> a
  $ hg ci -m '11: source change'

  $ hg mani
  0
  a
  b
  dest
  dir/b
  dir/c
  dir/d
  e

  $ glog -r 6:
  @  11 0c8927d1f7f4 (draft) "11: source change" files: a
  |
  o    10 9ccb7ee8d261 (draft) "10: source merge" files: a
  |\
  | o  9 f131b1518dba (draft) "9: source second branch" files: a
  | |
  o |  8 669cf0e74b50 (draft) "8: source first branch" files: a
  | |
  | o  7 e6d364a69ff1 (draft) "change in dest" files: dest
  |/
  o  6 0613c8e59a3d (public) "6: change a" files: a
  |
  $ cd ..

  $ hg convert --filemap filemap source dest --config convert.hg.revs=3:
  scanning source...
  sorting...
  converting...
  3 8: source first branch
  2 9: source second branch
  1 10: source merge
  0 11: source change

  $ glog -R dest
  o  9 8432d597b263 (draft) "11: source change" files: a
  |
  o    8 632ffacdcd6f (draft) "10: source merge" files: a
  |\
  | o  7 049cfee90ee6 (draft) "9: source second branch" files: a
  | |
  o |  6 9b6845e036e5 (draft) "8: source first branch" files: a
  | |
  | @  5 a2e0e3cc6d1d (draft) "change in dest" files: dest
  |/
  o  4 78814e84a217 (draft) "6: change a" files: a
  |
  o    3 f7cff662c5e5 (draft) "5: merge 2 and 3, copy b to dir/d" files: e
  |\
  | o  2 ab40a95b0072 (draft) "4: change a" files: a
  | |
  o |  1 bd51f17597bf (draft) "3: copy a to e, change b" files: b e
  |/
  o  0 a4a1dae0fe35 (draft) "1: add a and dir/b" files: 0 a
  
  $ cd ..

Two way tests

  $ hg init 0
  $ echo f > 0/f
  $ echo a > 0/a-only
  $ echo b > 0/b-only
  $ hg -R 0 ci -Aqm0

  $ cat << EOF > filemap-a
  > exclude b-only
  > EOF
  $ cat << EOF > filemap-b
  > exclude a-only
  > EOF
  $ hg convert --filemap filemap-a 0 a
  initializing destination a repository
  scanning source...
  sorting...
  converting...
  0 0
  $ hg -R a up -q
  $ echo a > a/f
  $ hg -R a ci -ma

  $ hg convert --filemap filemap-b 0 b
  initializing destination b repository
  scanning source...
  sorting...
  converting...
  0 0
  $ hg -R b up -q
  $ echo b > b/f
  $ hg -R b ci -mb

  $ tail */.hg/shamap
  ==> 0/.hg/shamap <==
  86f3f774ffb682bffb5dc3c1d3b3da637cb9a0d6 8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a
  dd9f218eb91fb857f2a62fe023e1d64a4e7812fe 8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a
  
  ==> a/.hg/shamap <==
  8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a 86f3f774ffb682bffb5dc3c1d3b3da637cb9a0d6
  
  ==> b/.hg/shamap <==
  8a028c7c77f6c7bd6d63bc3f02ca9f779eabf16a dd9f218eb91fb857f2a62fe023e1d64a4e7812fe

  $ hg convert a 0
  scanning source...
  sorting...
  converting...
  0 a

  $ hg convert b 0
  scanning source...
  sorting...
  converting...
  0 b

  $ hg -R 0 log -G
  o  changeset:   2:637fbbbe96b6
  |  tag:         tip
  |  parent:      0:8a028c7c77f6
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     b
  |
  | o  changeset:   1:ec7b9c96e692
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    summary:     a
  |
  @  changeset:   0:8a028c7c77f6
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     0
  
  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...

  $ hg -R 0 up -r1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo f >> 0/f
  $ hg -R 0 ci -mx

  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 x

  $ hg -R a log -G -T '{rev} {desc|firstline} ({files})\n'
  o  2 x (f)
  |
  @  1 a (f)
  |
  o  0 0 (a-only f)
  
  $ hg -R a mani -r tip
  a-only
  f

An additional round, demonstrating that unchanged files don't get converted

  $ echo f >> 0/f
  $ echo f >> 0/a-only
  $ hg -R 0 ci -m "extra f+a-only change"

  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 extra f+a-only change

  $ hg -R a log -G -T '{rev} {desc|firstline} ({files})\n'
  o  3 extra f+a-only change (f)
  |
  o  2 x (f)
  |
  @  1 a (f)
  |
  o  0 0 (a-only f)
  

Conversion after rollback

  $ hg -R a rollback -f
  repository tip rolled back to revision 2 (undo convert)

  $ hg convert --filemap filemap-b 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 extra f+a-only change

  $ hg -R a log -G -T '{rev} {desc|firstline} ({files})\n'
  o  3 extra f+a-only change (f)
  |
  o  2 x (f)
  |
  @  1 a (f)
  |
  o  0 0 (a-only f)
  
Convert with --full adds and removes files that didn't change

  $ echo f >> 0/f
  $ hg -R 0 ci -m "f"
  $ hg convert --filemap filemap-b --full 0 a --config convert.hg.revs=1::
  scanning source...
  sorting...
  converting...
  0 f
  $ hg -R a status --change tip
  M f
  A b-only
  R a-only