Mercurial > evolve

--- a/docs/obs-concept.rst	Wed Mar 28 11:07:02 2012 +0200
+++ b/docs/obs-concept.rst	Wed Mar 28 11:35:53 2012 +0200
@@ -1,17 +1,17 @@
------------------------------------------------------------
-Why Do We Need a New Concept
------------------------------------------------------------
+==============================
+ Why Do We Need a New Concept
+==============================

 Current DVCS are great tool to forge a series of flawless changeset on your own.
-But they perform poorly whe is comes to **share** work in progress and
+But they perform poorly when is comes to **share** work in progress and
 **collaborate** on such work in progress.

 When people forge new version of a changeset they create a new changeset and get
-ride of the original changeset. Difficultis to collaborate mostly came from the
+ride of the original changeset. Difficulties to collaborate mostly came from the
 way old content are *removed* from repository.

 Mercurial Approach: Strip
------------------------------------------------------
+=========================

 With current version of mercurial, every changesets that exist in your
 repository are *visible* and *meaningful*. To get ride of old changeset you
@@ -19,7 +19,7 @@
 called *strip*. After the *strip* the repository looks like if the changeset
 never existed.

-This approach is simple and effective but have a very big drawnback: You can
+This approach is simple and effective but have a very big drawback: You can
 remove changesets from **your repository only**. If strip exists in other
 repositories it will show of again and again. This only cure for this is to
 strip the offending changeset from all repository. And operation at best
@@ -29,23 +29,22 @@
 As consequence, **you can not rewrite something once you exchange it with
 others**. The old version will still exists along side the new one [#]_.

-Moreover backup are create stripped changeset in most case. This allow
-restoration of old changeset but the process is painful.
+Moreover stripping changesets creates backup bundles. This allows
+restoration of the deleted changesets, but the process is painful.

 Finally, as the repository format is not optimized for deletion. stripping a
-changeset may be slow in some situation.
-
+changeset may be slow in some situations.

 To sum up, the strip approach is very simple but does not handle interaction
 with the outer world. Which is unfortunate for a *Distributed* VCS.

-.. [#] various work around exists but they are work around with their own flow.
+.. [#] various work around exists but they require their own workflows which are distinct from the very elegant basic workflow of Mercurial.

 Git Approach: Overwrite Reference
------------------------------------------------------
+=================================

-Git approach for repository is a bit more complex: They can be any amount of
-changeset can exist in a repository. but **only changesets referenced by a git
+Git approach for repository is a bit more complex: Any number of
+changesets can exist in a repository. but **only changesets referenced by a git
 branch** are *visible* and *meaningful*.


@@ -59,51 +58,51 @@

     Only B and A are visible.

-This ease the process of getting ride of old changeset. You can just leave them
-in place and move the reference on the new one. You can then propagate those
-change by moving the git-branch on remote host, newer version overwritting the
-older one.
+This simplifies the process of getting rid of old changesets. You can
+just leave them in place and move the reference on the new one. You
+can then propagate that change by moving the git-branch on remote host
+with the newer version of the marker overwriting the older one.

-This approach goes a bit further but still have major drawback:
+This approach goes a bit further but still has a major drawback:


-Because you **overwrite** git-branch  you have no conflit resolution. The last
-to spoke win. This make collaboration on multiple changeset difficult because
-you can't merge concurent update on changeset.
+Because you **overwrite** the git-branch, you have no conflict resolution. The last
+to act wins. This makes collaboration on multiple changesets difficult because
+you can't merge concurrent updates on a changeset.

-Every overwrite is forced operation where the operator say "Yes I want this to
-replace that. On higly distributed environment user may end with conflicting
-reference with and no proper way to choose.
+Every overwrite is a forced operation where the operator say "Yes I want this to
+replace that. In highly distributed environments, a user may end up with conflicting
+references and no proper way to choose.

-Because of this way to visualize a repository,  git-branches are a very core
-part of git. This make user interface more complicated and move through history
-more constrainted.
+Because of this way to visualize a repository, git-branches are a core
+part of git, which makes the user interface more complicated and
+constrains the ways to move through history.

-Finally, even if all older changeset still exist in the repository acces to them
+Finally, even if all older changeset still exist in the repository, access to them
 is still painful.


------------------------------------------------------
-The Obsolete Marker Concept
------------------------------------------------------
+=============================
+ The Obsolete Marker Concept
+=============================


-As None of the concept was powerful enough to embrace the need to safely rewrite
-history, easily share and collaborate on mutable history we needed another one.
+As None of the concepts was powerful enough to fulfill the need of safely rewriting
+history, including easy sharing and collaborating on mutable history, we needed another one.


 Basic concept
------------------------------------------------------
+=============


-Every history rewriting operation  stores the information that old rewritten
-changesets has newer version available in a set of changeset.
+Every history rewriting operation stores the information that the old rewritten
+changeset is replaced by newer version in a given set of changeset.

-All basic history rewriting operation can create a appropriate obsolete marker.
+All basic history rewriting operation can create an appropriate obsolete marker.


 .. figure:: ./figures/example-1-update.*
@@ -147,16 +146,15 @@
 changesets to **1** old changeset.

 Basic Usage
------------------------------------------------------
+===========

-Obsolete markers create a perpendicular history: **a versionned version of the
-changeset graph**. This means that we can have the same feature we have for
+Obsolete markers create a perpendicular history: **a versioned changeset graph**. This means that offers the same features we have for
 versioned files but applied to changeset:

-First: we can display a **coherent view** of the history graph with only a
-single version of your changeset are displayed by the UI.
+First: we can display a **coherent view** of the history graph in which only a
+single version of your changesets are displayed by the UI.

-Second, because obsolete changeset content are still **available**. You can
+Second, because obsolete changeset content is still **available**. You can

     * **browse** the content of your obsolete commit,

@@ -172,52 +170,52 @@
 as conflicting changes on file.


-Detecting and solving tricky situation
------------------------------------------------------
+Detecting and solving tricky situations
+======================================

-History rewriting can lead to complex situation. Obsolete marker introduce a
-simple representation this complex reality. But people using complex workflow
-will one day or another you have to face the intrinsics complexity of some
-situation.
+History rewriting can lead to complex situations. Obsolete marker introduce a
+simple representation of this complex reality. But people using complex workflows
+will one day or another have to face the intrinsic complexity of some
+situations.

-This section describe possible situations, define precise set of changesets
-involved in such situation and explains how error case can we automatically
+This section describes possible situations, defines precise sets of changesets
+involved in such situations and explains how error cases can automatically be
 resolved using available information.


 obsolete changesets
-````````````````````
+-------------------

-Old changesets left behind by obsolete operation are said **obsolete**.
+Old changesets left behind by obsolete operation are called **obsolete**.

-With current version of mercurial, this *obsolete* part is stripped from the
-repository before the end of every rewritting operation.
+With the current version of mercurial, this *obsolete* part is stripped from the
+repository before the end of every rewriting operation.

 .. figure:: ./figures/error-obsolete.*

     Rebasing `B` and `C` on `A` (as `B'`, `C'`)

     This rebase operation added two obsolete markers from new changesets to old
-    changesets. These Two old changesets are now part of the *obsolete* part of the
+    changesets. These two old changesets are now part of the *obsolete* part of the
     history.

-In most case the obsolete set will be fully hidden to both UI and discovery so
-user do not have to care about them unless he wants to audit history rewriting
+In most cases, the obsolete set will be fully hidden to both UI and discovery so
+the user does not have to care about them unless he wants to audit the history rewriting
 operation.

 Unstable changesets
-```````````````````
+-------------------

-While exploring obsolete marker possibility a bit further you way end up with
-*obsolete* changeset with *non-obsolete* children. There is two common ways to
+While exploring the possibilities of the obsolete a bit further, you may end up with
+*obsolete* changeset which have *non-obsolete* children. There is two common ways to
 achieve this:

 * Pull a changeset based of an old version of a changeset [#]_.

 * Use a partial rewriting operation. For example amend on a changeset with
-  childrens.
+  children .

-*Non-obsolete* changeset based on *obsolete* one are said **unstable**
+*Non-obsolete* changeset based on *obsolete* one are called **unstable**

 .. figure:: ./figures/error-unstable.*

@@ -235,7 +233,7 @@
 the user of even carry them out for him.


-XXX details automatic resolution for
+XXX details on automatic resolution for

 * movement

@@ -245,17 +243,17 @@


 .. [#] For this to happen one needs to explicitly enable exchange of draft
-       changeset. See phase help for details.
+       changesets. See phase help for details.

 The two part of the obsolete set
-``````````````````````````````````````
+--------------------------------

-The previous section show that it could be two kinds of *obsolete* changeset:
+The previous section show that there can be two kinds of an *obsolete* changeset:


-* *obsolete* changeset with no or *obsolete* only descendants, said **extinct**.
+* an *obsolete* changeset with no or *obsolete* only descendants is called **extinct**.

-* *obsolete* changeset with *unstable* descendants, said **suspended**.
+* an *obsolete* changeset with *unstable* descendants is called **suspended**.


 .. figure:: ./figures/error-extinct.*
@@ -268,46 +266,46 @@


 Because nothing outside the obsolete set default on *extinct* changesets, they
-can be safely hidden in the UI and even garbage collected. *Suspended* changeset
-have to stay visible and available until they unstable descendant are rewritten
-in stable version.
+can be safely hidden in the UI and even garbage collected. *Suspended* changesets
+have to stay visible and available until their unstable descendant are rewritten
+into stable version.


-Conflicting rewriting
-``````````````````````
+Conflicting rewrites
+---------------------

 If people start to concurrently edit the same part of the history they will
-likely meet conflicting situation when a changeset have been rewritten in two
-different versions.
+likely meet conflicting situations when a changeset has been rewritten in two
+different ways.


 .. figure:: ./figures/error-conflicting.*

-    Conflicting rewriting of `A` into `A'` and `A''`
+    Conflicting rewrite of `A` into `A'` and `A''`

-This kind of conflict is easy to detect with obsolete marker because an obsolete
-changeset have more than one new version. It may be seen as the multiple heads
-case Mercurial warn you about on pull. It is resolved the same way by a merge of
+This kind of conflict is easy to detect with obsolete markers, because an obsolete
+changeset can have more than one new version. It may be seen as the multiple heads
+case which Mercurial warns you about on pull. It is resolved the same way by a merge of
 A' and A'' that will keep the same parent than `A'` and `A''` with two obsolete
 markers pointing to both `A` and `A'`

 .. warning::  TODO: Add a schema of the resolution. (merge A' and A'' with A as
               ancestor and graft the result of A^)

-Allowing multiple new changesets to obsolete a single one allow to distinct a
-splitted changeset from history rewriting conflict.
+Allowing multiple new changesets to obsolete a single one allows to differenciate
+split changesets from history rewriting conflicts.

 Reliable history
-``````````````````````
+----------------

-Obsolete marker really help to smooth rewriting operation process. However they
+Obsolete marker help to smooth rewriting operation process. However they
 do not change the fact that **you should only rewrite the mutable part of the
-history**. The phase concept enforce this rules by explicitly defining a
-public immutable set of changeset. Rewriting operation refuse to work on
-public changeset, but they is still some corner case where changesets
-rewritten in the past are made public.
+history**. The phase concept enforces this rule by explicitly defining a
+public immutable set of changesets. Rewriting operations refuse to work on
+public changesets, but there are still some corner cases where previously rewritten changesets
+are made public.

-Special rules apply for obsolete marker pointing to public changeset
+Special rules apply for obsolete markers pointing to public changesets

 * Public changesets are excluded from the obsolete set (public changeset are
   never hidden or candidate to garbage collection)
@@ -325,26 +323,26 @@


 Conclusion
-----------------
+==========

-Obsolete marker is a powerful concept that allow mercurial to safely handle
+The obsolete marker is a powerful concept that allows mercurial to safely handle
 history rewriting operations. It is a new type of relation between Mercurial
-changesets that track the result of history rewriting operations.
+changesets which tracks the result of history rewriting operations.

-This concept is simple to define and provides a very solid base to:
+This concept is simple to define and provides a very solid base for:


 - Very fast history rewriting operations,

-- auditable and reversible history rewritting process,
+- auditable and reversible history rewriting process,

 - clean final history,

-- share and collaborate on mutable part of the history,
+- sharing and collaborating on the mutable part of the history,

-- gracefully handle history rewriting conflict,
+- gracefully handling history rewriting conflicts,

-- allows various history rewriting UI to collaborate with a underlying common API.
+- various history rewriting UI’s collaborating with an underlying common API.

 .. list-table:: Comparison on solution [#]_
    :header-rows: 1