Mercurial > evolve

--- a/docs/obs-concept.rst	Tue Mar 27 16:55:47 2012 +0200
+++ b/docs/obs-concept.rst	Tue Mar 27 17:49:34 2012 +0200
@@ -2,51 +2,54 @@
 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
-**collaborate** on such work in progress.
+Current DVCS are great tools to forge a series of flawless changeset on your own.
+But they perform poorly when it comes to **sharing** some work in progress and
+**collaborating** 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
-way old content are *removed* from repository.
+When people forge a new version of a changeset they actually create a
+new changeset and get rid of the original changeset. Difficultis to
+collaborate mostly came from the way old content is *removed* from
+a 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
-rewrote mercurial remove them from the repository storage. with an operation
-called *strip*. After the *strip* the repository looks like if the changeset
-never existed.
+With the current version of mercurial, every changeset that exists in
+your repository is *visible* and *meaningful*. To delete old
+(rewritten) changesets, mercurial removes them from the repository
+storage with an operation called *strip*. After the *stripping*, the
+repository looks like if the changeset never existed.

-This approach is simple and effective but have a very big drawnback: 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
-impractical and in most case impossible!
-
+This approach is simple and effective except there is a very big
+drawback: you can remove changesets from **your repository only**. If
+a stripped changeset exists in another repository it touches, it will
+show up again. This is because a shared changeset becomes
+part of a shared global history. Stripping a changeset from all
+repositories is at best impractical and in most case impossible!

 As consequence, **you can not rewrite something once you exchange it with
-others**. The old version will still exists along side the new one [#]_.
+others**. The old version will still exist 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.
+However backups are created while stripping a changeset in most
+cases. This allow restoration of an old changeset but the process is
+painful.

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

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

-.. [#] various work around exists but they are work around with their own flow.
+.. [#] various workarounds exist but they are workarounds with their own flow.

 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
-branch** are *visible* and *meaningful*.
+The Git approach to repository structure is a bit more complex: there
+can be any amount of unrelated changesets in a repository, and **only
+changesets referenced by a git branch** are *visible* and
+*meaningful*.


 .. warning:: add a schema::
@@ -59,27 +62,26 @@

     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 ease 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 those changes by moving the git-branch on remote host,
+the newer versions overwritting the older ones.

-This approach goes a bit further but still have major drawback:
-
+This approach goes a bit further but still have 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** git-branch you have no conflit resolution. The last
+to speak wins. This makes collaboration on multiple changesets difficult because
+you can't merge concurent 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 says "Yes I
+want this to replace that". On a higly distributed environment, a user may
+end with conflicting references and with 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 very
+core part of git. This makes the user interface more complicated and
+moving through history more constrained.

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


@@ -88,20 +90,15 @@
 -----------------------------------------------------


-
-
-
-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 these concepts were powerful enough to embrace the need to
+safely share rewritten 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 old rewritten
+changesets has a newer version available in a set of changesets.

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

@@ -154,44 +151,47 @@
 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.
-
-Second, because obsolete changeset content are still **available**. You can
+single version of your changeset displayed by the UI.

-    * **browse** the content of your obsolete commit,
+Second, because obsolete changeset contents are still **available**,
+you can

-    * **compare** newer and older version of a changeset,
+    * **browse** the contents of your obsolete commits,
+
+    * **compare** newer and older versions of a changeset,

-    * **restore** content of previously obsolete changeset.
+    * **restore** contents of previously obsolete changesets.

-Finally, obsolete marker can be **exchanged between repositories**. You are able to
-share the result on your history rewriting operation with other and **collaborate
-on mutable part of the history**.
+Finally, the obsolete marker can be **exchanged between
+repositories**. You are able to share the result on your history
+rewriting operations with other prople and **collaborate on the
+mutable part of the history**.

-Conflicting history rewriting operation can be detected and **resolved** as easily
-as conflicting changes on file.
+Conflicting history rewriting operation can be detected and
+**resolved** as easily as conflicting changes on a 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. The obsolete marker
+introduces a simple representation for this complex reality. But
+people using complex workflows will one day or another have to face
+the intrinsic complexity of some real-world situation.

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


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

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

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

@@ -201,16 +201,16 @@
     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
-operation.
+In most cases the obsolete set will be fully hidden to both the UI and
+discovery, hence users do not have to care about them unless they want to
+audit history rewriting operations.

 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
-achieve this:
+While exploring the obsolete marker possibility a bit further you may
+end up with *obsolete* changeset with *non-obsolete* children. There
+are two common ways to achieve this:

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

@@ -230,9 +230,10 @@
     parent (`A`) is `A'`, We can deduce that we should rebase `B` on `A'` to get
     a stable history again.

-Proper warning should be issued when part of the history become unstable. UI
-will be able to use the obsolete marker to automatically suggest resolution to
-the user of even carry them out for him.
+Proper warnings should be issued when part of the history becomes
+unstable. The UI will be able to use the obsolete marker to
+automatically suggest a resolution to the user of even carry them out
+for him.


 XXX details automatic resolution for
@@ -247,11 +248,11 @@
 .. [#] For this to happen one needs to explicitly enable exchange of draft
        changeset. See phase help for details.

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

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

 * *obsolete* changeset with no or *obsolete* only descendants, said **extinct**.

@@ -277,7 +278,7 @@
 ``````````````````````

 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
+likely meet conflicting situations when a changeset have been rewritten in two
 different versions.


@@ -285,17 +286,18 @@

     Conflicting rewriting 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
-A' and A'' that will keep the same parent than `A'` and `A''` with two obsolete
+This kind of conflict is easy to detect with an obsolete marker
+because an obsolete changeset can have more than one new version. It
+may be seen as the multiple heads case. Mercurial warns you about this
+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
+distinguish a split changeset from an history rewriting conflict.

 Reliable history
 ``````````````````````
@@ -307,19 +309,18 @@
 public changeset, but they is still some corner case where changesets
 rewritten in the past are made public.

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

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

-* *newer* version of public changeset are said **latecomer** and highlighted as
-  error case.
-
+* *newer* version of a public changeset are said **latecomer** and highlighted as
+  an error case.

-Solving such error is easy. Because we know what changeset a *latecomer* try to
-rewrite, we can easily compute a smaller changeset containing only the change
-from the old *public* to the new *latecomer*.
-
+Solving such an error is easy. Because we know what changeset a
+*latecomer* tries to rewrite, we can easily compute a smaller
+changeset containing only the change from the old *public* to the new
+*latecomer*.

 .. warning:: add a schema

@@ -327,7 +328,7 @@
 Conclusion
 ----------------

-Obsolete marker is a powerful concept that allow mercurial to safely handle
+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.