view tests/test-unamend.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

Test for command `hg unamend` which lives in uncommit extension
===============================================================

  $ cat >> $HGRCPATH << EOF
  > [alias]
  > glog = log -G -T '{rev}:{node|short}  {desc}'
  > [experimental]
  > evolution = createmarkers, allowunstable
  > [extensions]
  > rebase =
  > amend =
  > uncommit =
  > EOF

Repo Setup

  $ hg init repo
  $ cd repo
  $ for ch in a b c d e f g h; do touch $ch; echo "foo" >> $ch; hg ci -Aqm "Added "$ch; done

  $ hg glog
  @  7:ec2426147f0e  Added h
  |
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
Trying to unamend when there was no amend done

  $ hg unamend
  abort: changeset must have one predecessor, found 0 predecessors
  [255]

Unamend on clean wdir and tip

  $ echo "bar" >> h
  $ hg amend

  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID c9fa1a715c1b7661c0fafb362a9f30bd75878d7d
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r c9fa1a715c1b h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar

  $ hg glog --hidden
  @  8:c9fa1a715c1b  Added h
  |
  | x  7:ec2426147f0e  Added h
  |/
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg unamend
  $ hg glog --hidden
  @  9:46d02d47eec6  Added h
  |
  | x  8:c9fa1a715c1b  Added h
  |/
  | x  7:ec2426147f0e  Added h
  |/
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg diff
  diff -r 46d02d47eec6 h
  --- a/h	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo
  +bar

  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 46d02d47eec6ca096b8dcab3f8f5579c40c3dd9a
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r 46d02d47eec6 h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

  $ hg status
  M h

  $ hg log -r . -T '{extras % "{extra}\n"}' --config alias.log=log
  branch=default
  unamend_source=c9fa1a715c1b7661c0fafb362a9f30bd75878d7d

Using unamend to undo an unamed (intentional)

  $ hg unamend
  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 850ddfc1bc662997ec6094ada958f01f0cc8070a
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r 850ddfc1bc66 h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar
  $ hg diff

Unamend on a dirty working directory

  $ echo "bar" >> a
  $ hg amend
  $ echo "foobar" >> a
  $ echo "bar" >> b
  $ hg status
  M a
  M b

  $ hg unamend

  $ hg status
  M a
  M b

  $ hg diff
  diff -r ec338db45d51 a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,3 @@
   foo
  +bar
  +foobar
  diff -r ec338db45d51 b
  --- a/b	Thu Jan 01 00:00:00 1970 +0000
  +++ b/b	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo
  +bar

Unamending an added file

  $ hg ci -m "Added things to a and b"
  $ echo foo > bar
  $ hg add bar
  $ hg amend

  $ hg unamend
  $ hg status
  A bar

  $ hg revert --all
  forgetting bar

Unamending a removed file

  $ hg remove a
  $ hg amend

  $ hg unamend
  $ hg status
  R a
  ? bar

  $ hg revert --all
  undeleting a

Unamending an added file with dirty wdir status

  $ hg add bar
  $ hg amend
  $ echo bar >> bar
  $ hg status
  M bar

  $ hg unamend
  $ hg status
  A bar
  $ hg diff
  diff -r 7f79409af972 bar
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/bar	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar

  $ hg revert --all
  forgetting bar

Unamending in middle of a stack

  $ hg glog
  @  19:7f79409af972  Added things to a and b
  |
  o  12:ec338db45d51  Added h
  |
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg up 5
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo bar >> f
  $ hg amend
  3 new orphan changesets
  $ hg rebase -s 6 -d . -q

  $ hg glog
  o  23:03ddd6fc5af1  Added things to a and b
  |
  o  22:3e7b64ee157b  Added h
  |
  o  21:49635b68477e  Added g
  |
  @  20:93f0e8ffab32  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  

  $ hg --config experimental.evolution=createmarkers unamend
  abort: cannot unamend changeset with children
  [255]

  $ hg unamend
  3 new orphan changesets

Trying to unamend a public changeset

  $ hg up -C 23
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg phase -r . -p
  1 new phase-divergent changesets
  $ hg unamend
  abort: cannot unamend public changesets
  (see 'hg help phases' for details)
  [255]

Testing whether unamend retains copies or not

  $ hg status
  ? bar

  $ hg mv a foo

  $ hg ci -m "Moved a to foo"
  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID cfef290346fbee5126313d7e1aab51d877679b09
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo

  $ hg mv b foobar
  $ hg diff --git
  diff --git a/b b/foobar
  rename from b
  rename to foobar
  $ hg amend

  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID eca050985275bb271ce3092b54e56ea5c85d29a3
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo
  diff --git a/b b/foobar
  rename from b
  rename to foobar

  $ hg mv c wat
  $ hg unamend

Retained copies in new prdecessor commit

  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 552e3af4f01f620f88ca27be1f898316235b736a
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo

Retained copies in working directoy

  $ hg diff --git
  diff --git a/b b/foobar
  rename from b
  rename to foobar
  diff --git a/c b/wat
  rename from c
  rename to wat