view tests/test-import-bypass.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.

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "purge=" >> $HGRCPATH

  $ shortlog() {
  >     hg log -G --template '{rev}:{node|short} {author} {date|hgdate} - {branch} - {desc|firstline}\n'
  > }

Test --bypass with other options

  $ hg init repo-options
  $ cd repo-options
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ echo a >> a
  $ hg branch foo
  marked working directory as branch foo
  (branches are permanent and global, did you want a bookmark?)
  $ hg ci -Am changea
  $ hg export . > ../test.diff
  $ hg up null
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

Test importing an existing revision
(this also tests that "hg import" disallows combination of '--exact'
and '--edit')

  $ hg import --bypass --exact --edit ../test.diff
  abort: cannot use --exact with --edit
  [255]
  $ hg import --bypass --exact ../test.diff
  applying ../test.diff
  $ shortlog
  o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |
  o  0:07f494440405 test 0 0 - default - adda
  

Test failure without --exact

  $ hg import --bypass ../test.diff
  applying ../test.diff
  unable to find 'a' for patching
  abort: patch failed to apply
  [255]
  $ hg st
  $ shortlog
  o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |
  o  0:07f494440405 test 0 0 - default - adda
  

Test --user, --date and --message

  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg import --bypass --u test2 -d '1 0' -m patch2 ../test.diff
  applying ../test.diff
  $ cat .hg/last-message.txt
  patch2 (no-eol)
  $ shortlog
  o  2:2e127d1da504 test2 1 0 - default - patch2
  |
  | o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |/
  @  0:07f494440405 test 0 0 - default - adda
  
  $ hg rollback
  repository tip rolled back to revision 1 (undo import)

Test --import-branch
(this also tests that editor is not invoked for '--bypass', if the
patch contains the commit message, regardless of '--edit')

  $ HGEDITOR=cat hg import --bypass --import-branch --edit ../test.diff
  applying ../test.diff
  $ shortlog
  o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |
  @  0:07f494440405 test 0 0 - default - adda
  
  $ hg rollback
  repository tip rolled back to revision 1 (undo import)

Test --strip

  $ hg import --bypass --strip 0 - <<EOF
  > # HG changeset patch
  > # User test
  > # Date 0 0
  > # Branch foo
  > # Node ID 4e322f7ce8e3e4203950eac9ece27bf7e45ffa6c
  > # Parent  07f4944404050f47db2e5c5071e0e84e7a27bba9
  > changea
  > 
  > diff -r 07f494440405 -r 4e322f7ce8e3 a
  > --- a	Thu Jan 01 00:00:00 1970 +0000
  > +++ a	Thu Jan 01 00:00:00 1970 +0000
  > @@ -1,1 +1,2 @@
  >  a
  > +a
  > EOF
  applying patch from stdin
  $ hg rollback
  repository tip rolled back to revision 1 (undo import)

Test --strip with --bypass

  $ mkdir -p dir/dir2
  $ echo bb > dir/dir2/b
  $ echo cc > dir/dir2/c
  $ echo d > dir/d
  $ hg ci -Am 'addabcd'
  adding dir/d
  adding dir/dir2/b
  adding dir/dir2/c
  $ shortlog
  @  2:d805bc8236b6 test 0 0 - default - addabcd
  |
  | o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |/
  o  0:07f494440405 test 0 0 - default - adda
  
  $ hg import --bypass --strip 2 --prefix dir/ - <<EOF
  > # HG changeset patch
  > # User test
  > # Date 0 0
  > # Branch foo
  > changeabcd
  > 
  > diff --git a/foo/a b/foo/a
  > new file mode 100644
  > --- /dev/null
  > +++ b/foo/a
  > @@ -0,0 +1 @@
  > +a
  > diff --git a/foo/dir2/b b/foo/dir2/b2
  > rename from foo/dir2/b
  > rename to foo/dir2/b2
  > diff --git a/foo/dir2/c b/foo/dir2/c
  > --- a/foo/dir2/c
  > +++ b/foo/dir2/c
  > @@ -0,0 +1 @@
  > +cc
  > diff --git a/foo/d b/foo/d
  > deleted file mode 100644
  > --- a/foo/d
  > +++ /dev/null
  > @@ -1,1 +0,0 @@
  > -d
  > EOF
  applying patch from stdin

  $ shortlog
  o  3:5bd46886ca3e test 0 0 - default - changeabcd
  |
  @  2:d805bc8236b6 test 0 0 - default - addabcd
  |
  | o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |/
  o  0:07f494440405 test 0 0 - default - adda
  
  $ hg diff --change 3 --git
  diff --git a/dir/a b/dir/a
  new file mode 100644
  --- /dev/null
  +++ b/dir/a
  @@ -0,0 +1,1 @@
  +a
  diff --git a/dir/d b/dir/d
  deleted file mode 100644
  --- a/dir/d
  +++ /dev/null
  @@ -1,1 +0,0 @@
  -d
  diff --git a/dir/dir2/b b/dir/dir2/b2
  rename from dir/dir2/b
  rename to dir/dir2/b2
  diff --git a/dir/dir2/c b/dir/dir2/c
  --- a/dir/dir2/c
  +++ b/dir/dir2/c
  @@ -1,1 +1,2 @@
   cc
  +cc
  $ hg -q --config extensions.strip= strip .

Test unsupported combinations

  $ hg import --bypass --no-commit ../test.diff
  abort: cannot use --no-commit with --bypass
  [255]
  $ hg import --bypass --similarity 50 ../test.diff
  abort: cannot use --similarity with --bypass
  [255]
  $ hg import --exact --prefix dir/ ../test.diff
  abort: cannot use --exact with --prefix
  [255]

Test commit editor
(this also tests that editor is invoked, if the patch doesn't contain
the commit message, regardless of '--edit')

  $ cat > ../test.diff <<EOF
  > diff -r 07f494440405 -r 4e322f7ce8e3 a
  > --- a/a	Thu Jan 01 00:00:00 1970 +0000
  > +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  > @@ -1,1 +1,2 @@
  > -a
  > +b
  > +c
  > EOF
  $ HGEDITOR=cat hg import --bypass ../test.diff
  applying ../test.diff
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'default'
  HG: changed a
  abort: empty commit message
  [255]

Test patch.eol is handled
(this also tests that editor is not invoked for '--bypass', if the
commit message is explicitly specified, regardless of '--edit')

  $ $PYTHON -c 'file("a", "wb").write("a\r\n")'
  $ hg ci -m makeacrlf
  $ HGEDITOR=cat hg import -m 'should fail because of eol' --edit --bypass ../test.diff
  applying ../test.diff
  patching file a
  Hunk #1 FAILED at 0
  abort: patch failed to apply
  [255]
  $ hg --config patch.eol=auto import -d '0 0' -m 'test patch.eol' --bypass ../test.diff
  applying ../test.diff
  $ shortlog
  o  3:c606edafba99 test 0 0 - default - test patch.eol
  |
  @  2:872023de769d test 0 0 - default - makeacrlf
  |
  | o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |/
  o  0:07f494440405 test 0 0 - default - adda
  

Test applying multiple patches

  $ hg up -qC 0
  $ echo e > e
  $ hg ci -Am adde
  adding e
  created new head
  $ hg export . > ../patch1.diff
  $ hg up -qC 1
  $ echo f > f
  $ hg ci -Am addf
  adding f
  $ hg export . > ../patch2.diff
  $ cd ..
  $ hg clone -r1 repo-options repo-multi1
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 1 files
  updating to branch foo
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd repo-multi1
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg import --bypass ../patch1.diff ../patch2.diff
  applying ../patch1.diff
  applying ../patch2.diff
  $ shortlog
  o  3:bc8ca3f8a7c4 test 0 0 - default - addf
  |
  o  2:16581080145e test 0 0 - default - adde
  |
  | o  1:4e322f7ce8e3 test 0 0 - foo - changea
  |/
  @  0:07f494440405 test 0 0 - default - adda
  

Test applying multiple patches with --exact

  $ cd ..
  $ hg clone -r1 repo-options repo-multi2
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 1 files
  updating to branch foo
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd repo-multi2
  $ hg import --bypass --exact ../patch1.diff ../patch2.diff
  applying ../patch1.diff
  applying ../patch2.diff
  $ shortlog
  o  3:d60cb8989666 test 0 0 - foo - addf
  |
  | o  2:16581080145e test 0 0 - default - adde
  | |
  @ |  1:4e322f7ce8e3 test 0 0 - foo - changea
  |/
  o  0:07f494440405 test 0 0 - default - adda
  

  $ cd ..

Test avoiding editor invocation at applying the patch with --exact
even if commit message is empty

  $ cd repo-options

  $ echo a >> a
  $ hg commit -m ' '
  $ hg tip -T "{node}\n"
  1b77bc7d1db9f0e7f1716d515b630516ab386c89
  $ hg export -o ../empty-log.diff .
  $ hg update -q -C ".^1"
  $ hg --config extensions.strip= strip -q tip
  $ HGEDITOR=cat hg import --exact --bypass ../empty-log.diff
  applying ../empty-log.diff
  $ hg tip -T "{node}\n"
  1b77bc7d1db9f0e7f1716d515b630516ab386c89

  $ cd ..

#if symlink execbit

Test complicated patch with --exact

  $ hg init repo-exact
  $ cd repo-exact
  $ echo a > a
  $ echo c > c
  $ echo d > d
  $ echo e > e
  $ echo f > f
  $ chmod +x f
  $ ln -s c linkc
  $ hg ci -Am t
  adding a
  adding c
  adding d
  adding e
  adding f
  adding linkc
  $ hg cp a aa1
  $ echo b >> a
  $ echo b > b
  $ hg add b
  $ hg cp a aa2
  $ echo aa >> aa2
  $ chmod +x e
  $ chmod -x f
  $ ln -s a linka
  $ hg rm d
  $ hg rm linkc
  $ hg mv c cc
  $ hg ci -m patch
  $ hg export --git . > ../test.diff
  $ hg up -C null
  0 files updated, 0 files merged, 7 files removed, 0 files unresolved
  $ hg purge
  $ hg st
  $ hg import --bypass --exact ../test.diff
  applying ../test.diff

The patch should have matched the exported revision and generated no additional
data. If not, diff both heads to debug it.

  $ shortlog
  o  1:2978fd5c8aa4 test 0 0 - default - patch
  |
  o  0:a0e19e636a43 test 0 0 - default - t
  
#endif

  $ cd ..