(for details from a source code point of view, see WhatGoesWhere)

<<TableOfContents>>

== Data structures ==

'''Nodeids''' are unique ids that represent the contents of a file ''and'' its
position in the project history. See [[Nodeid]].

A '''revlog''', for example {{{.hg/data/somefile.d}}}, is the most important
data structure and represents all versions of a file. See [[Revlog]].

A '''manifest''' describes the state of a project by listing each file and
its nodeid to specify which version.  See [[Manifest]].

A '''changeset''' lists all files changed in a checkin along with a change
description and metadata like user and date. See [[ChangeSet]].

== Putting it all together ==

We now have enough information to see how this all works together. To look up a given revision of a file:

 * look up the changeset in the changeset index
 * reconstruct the changeset data from the revlog
 * look up the manifest nodeid from the changeset in the manifest index
 * reconstruct the manifest for that revision
 * find the nodeid for the file in that revision
 * look up the revision of that file in the file's index
 * reconstruct the file revision from the revlog

If we want to go the other way and find the changeset associated with a given file revision, we follow the linkrev.

{{{

   .--------linkrev-------------.
   v                            |
.---------.    .--------.    .--------.
|changeset| .->|manifest| .->|file    |---.
|index    | |  |index   | |  |index   |   |--.
`---------' |  `--------' |  `--------'   |  |
    |       |      |      |     | `-------'  |
    V       |      V      |     V    `-------'
.---------. |  .--------. |  .---------.
|changeset|-'  |manifest|-'  |file     |
|data     |    |data    |    |revision |
`---------'    `--------'    `---------'

}}}

== Tracking Working Directory State ==

The other piece of Mercurial is the [[WorkingDirectory|working directory]]. Mercurial tracks various information about the working directory. See DirState.

== Merging ==

See [[Merge]].

== Rollback ==

See [[Rollback]].

== References ==
 * ''"Towards a Better SCM: Revlog and Mercurial"'', Matt Mackall ([[attachment:Presentations/ols-mercurial-paper.pdf|PDF]])
 * ''[[http://hgbook.red-bean.com/hgbookch4.html#x8-640004|"Behind the scenes"]]'' in ''[[http://hgbook.red-bean.com/hgbook.html|"Distributed revision control with Mercurial"]]'', Bryan O’Sullivan

see also: [[Presentations]]
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CategoryInternals