view tests/test-split.t @ 40022:33eb670e2834

wireprotov2: define semantics for content redirects

When I implemented the clonebundles feature and deployed it on
hg.mozilla.org using Amazon S3 as a content server, server-side CPU
and bandwidth usage dropped off a cliff and a ton of server scaling
headaches went away pretty much the instant clients with support for
clonebundles were rolled out to Firefox CI.

An obvious takeaway from that experience was that offloading server
load to scalable file servers - potentially backed by a CDN - is a
really good idea. Another takeaway was that Mercurial's wire protocol
wasn't in a good position to support data offload generally.

In wire protocol version 1, there isn't a mechanism in the protocol to
say "grab the data from over here instead." For HTTP, we could teach
the client to follow HTTP redirects. Or we could invent a media type
that encoded redirects inline. But for SSH, we were pretty much out of
luck because that protocol wasn't very flexible.

Wire protocol version 2 offers the opportunity to do something better.

The recent generic server-side content caching layer in the wire
protocol version 2 server demonstrated that it is possible to have
drop-in caching of responses to command requests. This by itself
adds tons of value and already makes the built-in server much more
scalable. But I don't want to stop there.

The existing server-side caching implementation has a big weakness:
it requires the server to send data to the client. This means that
the Mercurial server is potentially sending gigabytes of data to
thousands of clients. This is problematic because compared to scaling
static file servers, scaling dynamic servers is *hard*.

A solution to this is to "offload" serving of content to something
that isn't the Mercurial server. By offloading content serving, you
turn the Mercurial server from a centralized monolithic service to
a distributed mostly-indexing service. Assuming high rates of content
offload, this should drastically reduce the total work performed by
the Mercurial server, both in terms of CPU and data transfer. This
will make Mercurial servers vastly easier to scale.

This commit defines the semantics for "content redirects" in wire
protocol version 2. Essentially:

* Servers advertise the set of locations a response could be served
  from.
* When making requests, clients advertise the set of locations they
  are willing to fetch content from.
* Servers can then replace the inline response with one that says
  "get the response from over here instead."

This feature - when fully implemented - will allow extending the
server-side caching layer to facilitate such things as integrating
your server-side cache with a scalable blob store (such as S3 or
a CDN) and offloading most data transfer to that external service.

This feature could also be leveraged for load balancing. e.g.
requests could come into a central server and then get redirected
to an available mirror depending on server availability or locality.
There's tons of potential :)

Differential Revision: https://phab.mercurial-scm.org/D4774

#testcases obsstore-on obsstore-off

  $ cat > $TESTTMP/editor.py <<EOF
  > #!"$PYTHON"
  > import os
  > import sys
  > path = os.path.join(os.environ['TESTTMP'], 'messages')
  > messages = open(path).read().split('--\n')
  > prompt = open(sys.argv[1]).read()
  > sys.stdout.write(''.join('EDITOR: %s' % l for l in prompt.splitlines(True)))
  > sys.stdout.flush()
  > with open(sys.argv[1], 'w') as f:
  >    f.write(messages[0])
  > with open(path, 'w') as f:
  >    f.write('--\n'.join(messages[1:]))
  > EOF

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > drawdag=$TESTDIR/drawdag.py
  > split=
  > [ui]
  > interactive=1
  > color=no
  > paginate=never
  > [diff]
  > git=1
  > unified=0
  > [alias]
  > glog=log -G -T '{rev}:{node|short} {desc} {bookmarks}\n'
  > EOF

#if obsstore-on
  $ cat >> $HGRCPATH <<EOF
  > [experimental]
  > evolution=all
  > EOF
#endif

  $ hg init a
  $ cd a

Nothing to split

  $ hg split
  nothing to split
  [1]

  $ hg commit -m empty --config ui.allowemptycommit=1
  $ hg split
  abort: cannot split an empty revision
  [255]

  $ rm -rf .hg
  $ hg init

Cannot split working directory

  $ hg split -r 'wdir()'
  abort: cannot split working directory
  [255]

Generate some content.  The sed filter drop CR on Windows, which is dropped in
the a > b line.

  $ $TESTDIR/seq.py 1 5 | sed 's/\r$//' >> a
  $ hg ci -m a1 -A a -q
  $ hg bookmark -i r1
  $ sed 's/1/11/;s/3/33/;s/5/55/' a > b
  $ mv b a
  $ hg ci -m a2 -q
  $ hg bookmark -i r2

Cannot split a public changeset

  $ hg phase --public -r 'all()'
  $ hg split .
  abort: cannot split public changeset
  (see 'hg help phases' for details)
  [255]

  $ hg phase --draft -f -r 'all()'

Cannot split while working directory is dirty

  $ touch dirty
  $ hg add dirty
  $ hg split .
  abort: uncommitted changes
  [255]
  $ hg forget dirty
  $ rm dirty

Make a clean directory for future tests to build off of

  $ cp -R . ../clean

Split a head

  $ hg bookmark r3

  $ hg split 'all()'
  abort: cannot split multiple revisions
  [255]

  $ runsplit() {
  > cat > $TESTTMP/messages <<EOF
  > split 1
  > --
  > split 2
  > --
  > split 3
  > EOF
  > cat <<EOF | hg split "$@"
  > y
  > y
  > y
  > y
  > y
  > y
  > EOF
  > }

  $ HGEDITOR=false runsplit
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -5,1 +5,1 @@ 4
  -5
  +55
  record this change to 'a'? [Ynesfdaq?] y
  
  transaction abort!
  rollback completed
  abort: edit failed: false exited with status 1
  [255]
  $ hg status

  $ HGEDITOR="\"$PYTHON\" $TESTTMP/editor.py"
  $ runsplit
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -5,1 +5,1 @@ 4
  -5
  +55
  record this change to 'a'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 1df0d5c5a3ab. Write commit message for the first split changeset.
  EDITOR: a2
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: changed a
  created new head
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -3,1 +3,1 @@ 2
  -3
  +33
  record this change to 'a'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 1df0d5c5a3ab. So far it has been split into:
  EDITOR: HG: - e704349bd21b: split 1
  EDITOR: HG: Write commit message for the next split changeset.
  EDITOR: a2
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: changed a
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -1,1 +1,1 @@
  -1
  +11
  record this change to 'a'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 1df0d5c5a3ab. So far it has been split into:
  EDITOR: HG: - e704349bd21b: split 1
  EDITOR: HG: - a09ad58faae3: split 2
  EDITOR: HG: Write commit message for the next split changeset.
  EDITOR: a2
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: changed a
  saved backup bundle to $TESTTMP/a/.hg/strip-backup/1df0d5c5a3ab-8341b760-split.hg (obsstore-off !)

#if obsstore-off
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        3:00eebaf8d2e2
   * r3                        3:00eebaf8d2e2
  $ hg glog -p
  @  3:00eebaf8d2e2 split 3 r2 r3
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -1,1 +1,1 @@
  |  -1
  |  +11
  |
  o  2:a09ad58faae3 split 2
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -3,1 +3,1 @@
  |  -3
  |  +33
  |
  o  1:e704349bd21b split 1
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -5,1 +5,1 @@
  |  -5
  |  +55
  |
  o  0:a61bcde8c529 a1 r1
     diff --git a/a b/a
     new file mode 100644
     --- /dev/null
     +++ b/a
     @@ -0,0 +1,5 @@
     +1
     +2
     +3
     +4
     +5
  
#else
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        4:00eebaf8d2e2
   * r3                        4:00eebaf8d2e2
  $ hg glog
  @  4:00eebaf8d2e2 split 3 r2 r3
  |
  o  3:a09ad58faae3 split 2
  |
  o  2:e704349bd21b split 1
  |
  o  0:a61bcde8c529 a1 r1
  
#endif

Split a head while working parent is not that head

  $ cp -R $TESTTMP/clean $TESTTMP/b
  $ cd $TESTTMP/b

  $ hg up 0 -q
  $ hg bookmark r3

  $ runsplit tip >/dev/null

#if obsstore-off
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        3:00eebaf8d2e2
   * r3                        0:a61bcde8c529
  $ hg glog
  o  3:00eebaf8d2e2 split 3 r2
  |
  o  2:a09ad58faae3 split 2
  |
  o  1:e704349bd21b split 1
  |
  @  0:a61bcde8c529 a1 r1 r3
  
#else
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        4:00eebaf8d2e2
   * r3                        0:a61bcde8c529
  $ hg glog
  o  4:00eebaf8d2e2 split 3 r2
  |
  o  3:a09ad58faae3 split 2
  |
  o  2:e704349bd21b split 1
  |
  @  0:a61bcde8c529 a1 r1 r3
  
#endif

Split a non-head

  $ cp -R $TESTTMP/clean $TESTTMP/c
  $ cd $TESTTMP/c
  $ echo d > d
  $ hg ci -m d1 -A d
  $ hg bookmark -i d1
  $ echo 2 >> d
  $ hg ci -m d2
  $ echo 3 >> d
  $ hg ci -m d3
  $ hg bookmark -i d3
  $ hg up '.^' -q
  $ hg bookmark d2
  $ cp -R . ../d

  $ runsplit -r 1 | grep rebasing
  rebasing 2:b5c5ea414030 "d1" (d1)
  rebasing 3:f4a0a8d004cc "d2" (d2)
  rebasing 4:777940761eba "d3" (d3)
#if obsstore-off
  $ hg bookmark
     d1                        4:c4b449ef030e
   * d2                        5:c9dd00ab36a3
     d3                        6:19f476bc865c
     r1                        0:a61bcde8c529
     r2                        3:00eebaf8d2e2
  $ hg glog -p
  o  6:19f476bc865c d3 d3
  |  diff --git a/d b/d
  |  --- a/d
  |  +++ b/d
  |  @@ -2,0 +3,1 @@
  |  +3
  |
  @  5:c9dd00ab36a3 d2 d2
  |  diff --git a/d b/d
  |  --- a/d
  |  +++ b/d
  |  @@ -1,0 +2,1 @@
  |  +2
  |
  o  4:c4b449ef030e d1 d1
  |  diff --git a/d b/d
  |  new file mode 100644
  |  --- /dev/null
  |  +++ b/d
  |  @@ -0,0 +1,1 @@
  |  +d
  |
  o  3:00eebaf8d2e2 split 3 r2
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -1,1 +1,1 @@
  |  -1
  |  +11
  |
  o  2:a09ad58faae3 split 2
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -3,1 +3,1 @@
  |  -3
  |  +33
  |
  o  1:e704349bd21b split 1
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -5,1 +5,1 @@
  |  -5
  |  +55
  |
  o  0:a61bcde8c529 a1 r1
     diff --git a/a b/a
     new file mode 100644
     --- /dev/null
     +++ b/a
     @@ -0,0 +1,5 @@
     +1
     +2
     +3
     +4
     +5
  
#else
  $ hg bookmark
     d1                        8:c4b449ef030e
   * d2                        9:c9dd00ab36a3
     d3                        10:19f476bc865c
     r1                        0:a61bcde8c529
     r2                        7:00eebaf8d2e2
  $ hg glog
  o  10:19f476bc865c d3 d3
  |
  @  9:c9dd00ab36a3 d2 d2
  |
  o  8:c4b449ef030e d1 d1
  |
  o  7:00eebaf8d2e2 split 3 r2
  |
  o  6:a09ad58faae3 split 2
  |
  o  5:e704349bd21b split 1
  |
  o  0:a61bcde8c529 a1 r1
  
#endif

Split a non-head without rebase

  $ cd $TESTTMP/d
#if obsstore-off
  $ runsplit -r 1 --no-rebase
  abort: cannot split changeset with children without rebase
  [255]
#else
  $ runsplit -r 1 --no-rebase >/dev/null
  3 new orphan changesets
  $ hg bookmark
     d1                        2:b5c5ea414030
   * d2                        3:f4a0a8d004cc
     d3                        4:777940761eba
     r1                        0:a61bcde8c529
     r2                        7:00eebaf8d2e2

  $ hg glog
  o  7:00eebaf8d2e2 split 3 r2
  |
  o  6:a09ad58faae3 split 2
  |
  o  5:e704349bd21b split 1
  |
  | *  4:777940761eba d3 d3
  | |
  | @  3:f4a0a8d004cc d2 d2
  | |
  | *  2:b5c5ea414030 d1 d1
  | |
  | x  1:1df0d5c5a3ab a2
  |/
  o  0:a61bcde8c529 a1 r1
  
#endif

Split a non-head with obsoleted descendants

#if obsstore-on
  $ hg init $TESTTMP/e
  $ cd $TESTTMP/e
  $ hg debugdrawdag <<'EOS'
  >   H I   J
  >   | |   |
  >   F G1 G2  # amend: G1 -> G2
  >   | |  /   # prune: F
  >   C D E
  >    \|/
  >     B
  >     |
  >     A
  > EOS
  2 new orphan changesets
  $ eval `hg tags -T '{tag}={node}\n'`
  $ rm .hg/localtags
  $ hg split $B --config experimental.evolution=createmarkers
  abort: split would leave orphaned changesets behind
  [255]
  $ cat > $TESTTMP/messages <<EOF
  > Split B
  > EOF
  $ cat <<EOF | hg split $B
  > y
  > y
  > EOF
  diff --git a/B b/B
  new file mode 100644
  examine changes to 'B'? [Ynesfdaq?] y
  
  @@ -0,0 +1,1 @@
  +B
  \ No newline at end of file
  record this change to 'B'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 112478962961. Write commit message for the first split changeset.
  EDITOR: B
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: added B
  created new head
  rebasing 2:26805aba1e60 "C"
  rebasing 3:be0ef73c17ad "D"
  rebasing 4:49cb92066bfd "E"
  rebasing 7:97a6268cc7ef "G2"
  rebasing 10:e2f1e425c0db "J"
  $ hg glog -r 'sort(all(), topo)'
  o  16:556c085f8b52 J
  |
  o  15:8761f6c9123f G2
  |
  o  14:a7aeffe59b65 E
  |
  | o  13:e1e914ede9ab D
  |/
  | o  12:01947e9b98aa C
  |/
  o  11:0947baa74d47 Split B
  |
  | *  9:88ede1d5ee13 I
  | |
  | x  6:af8cbf225b7b G1
  | |
  | x  3:be0ef73c17ad D
  | |
  | | *  8:74863e5b5074 H
  | | |
  | | x  5:ee481a2a1e69 F
  | | |
  | | x  2:26805aba1e60 C
  | |/
  | x  1:112478962961 B
  |/
  o  0:426bada5c675 A
  
#endif

Preserve secret phase in split

  $ cp -R $TESTTMP/clean $TESTTMP/phases1
  $ cd $TESTTMP/phases1
  $ hg phase --secret -fr tip
  $ hg log -T '{short(node)} {phase}\n'
  1df0d5c5a3ab secret
  a61bcde8c529 draft
  $ runsplit tip >/dev/null
  $ hg log -T '{short(node)} {phase}\n'
  00eebaf8d2e2 secret
  a09ad58faae3 secret
  e704349bd21b secret
  a61bcde8c529 draft

Do not move things to secret even if phases.new-commit=secret

  $ cp -R $TESTTMP/clean $TESTTMP/phases2
  $ cd $TESTTMP/phases2
  $ cat >> .hg/hgrc <<EOF
  > [phases]
  > new-commit=secret
  > EOF
  $ hg log -T '{short(node)} {phase}\n'
  1df0d5c5a3ab draft
  a61bcde8c529 draft
  $ runsplit tip >/dev/null
  $ hg log -T '{short(node)} {phase}\n'
  00eebaf8d2e2 draft
  a09ad58faae3 draft
  e704349bd21b draft
  a61bcde8c529 draft