5
5
This document describes the key classes and concepts within Bazaar. It is
6
6
intended to be useful to people working on the Bazaar codebase, or to
7
7
people writing plugins. People writing plugins may also like to read the
8
guide to `Integrating with Bazaar <integration.html>`_ for some specific recipes.
10
There's some overlap between this and the `Core Concepts`_ section of the
11
user guide, but this document is targetted to people interested in the
12
internals. In particular the user guide doesn't go any deeper than
13
"revision", because regular users don't care about lower-level details
14
like inventories, but this guide does.
8
guide to `Integrating with Bazaar <integration.html>`_ for some specific
16
11
If you have any questions, or if something seems to be incorrect, unclear
17
or missing, please talk to us in ``irc://irc.freenode.net/#bzr``, write to
18
the Bazaar mailing list, or simply file a bug report.
12
or missing, please talk to us in ``irc://irc.freenode.net/#bzr``, or write
13
to the Bazaar mailing list.
27
All IDs are globally unique identifiers. Inside bzrlib they are almost
28
always represented as UTF-8 encoded bytestrings (i.e. ``str`` objects).
32
:Revision IDs: The unique identifier of a single revision, such as
33
``pqm@pqm.ubuntu.com-20110201161347-ao76mv267gc1b5v2``
34
:File IDs: The unique identifier of a single file. It is allocated when
35
a user does ``bzr add`` and is unchanged by renames.
37
By convention, in the bzrlib API, parameters of methods that are expected
38
to be IDs (as opposed to keys, revision numbers, or some other handle)
39
will end in ``id``, e.g. ``revid`` or ``file_id``.
44
A composite of one or more ID elements. E.g. a (file-id, revision-id)
45
pair is the key to the "texts" store, but a single element key of
46
(revision-id) is the key to the "revisions" store.
22
When using bzrlib within the ``bzr`` program (for instance as a bzr
23
plugin), bzrlib's global state is already available for use.
28
To use bzrlib outside of ``bzr`` some global state needs to be setup.
29
bzrlib needs ways to handle user input, passwords, a place to emit
30
progress bars, logging setup appropriately for your program. The easiest
31
way to set all this up in the same fashion ``bzr`` does is to call
32
``bzrlib.initialize``. This returns a context manager within which bzrlib
33
functions will work correctly. See the pydoc for ``bzrlib.initialize`` for
34
more information. In Python 2.4 the ``with`` keyword is not supported and
35
so you need to use the context manager manually::
37
# This sets up your ~/.bzr.log, ui factory and so on and so forth. It is
38
# not safe to use as a doctest.
39
library_state = bzrlib.initialize()
40
library_state.__enter__()
45
library_state.__exit__(None, None, None)
99
98
elsewhere. Information that Transports return, such as from ``list_dir``,
100
99
is also in the form of URL components.
107
* `Developer guide to bzrlib transports <transports.html>`_
108
* API docs for ``bzrlib.transport.Transport``
113
A representation of a directory of files (and other directories and
114
symlinks etc). The most important kinds of Tree are:
116
:WorkingTree: the files on disk editable by the user
117
:RevisionTree: a tree as recorded at some point in the past
119
Trees can map file paths to file-ids and vice versa (although trees such
120
as WorkingTree may have unversioned files not described in that mapping).
121
Trees have an inventory and parents (an ordered list of zero or more
131
108
Responsibilities:
133
* Maintaining a WorkingTree on disk at a file path.
134
* Maintaining the basis inventory (the inventory of the last commit done)
135
* Maintaining the working inventory.
136
* Maintaining the pending merges list.
137
* Maintaining the stat cache.
138
* Maintaining the last revision the working tree was updated to.
139
* Knows where its Branch is located.
110
* Maintaining a WorkingTree on disk at a file path.
111
* Maintaining the basis inventory (the inventory of the last commit done)
112
* Maintaining the working inventory.
113
* Maintaining the pending merges list.
114
* Maintaining the stat cache.
115
* Maintaining the last revision the working tree was updated to.
116
* Knows where its Branch is located.
144
* an MutableInventory
145
* local access to the working tree
121
* an MutableInventory
122
* local access to the working tree
154
130
A Branch is responsible for:
156
* Holding user preferences that are set in a Branch.
157
* Holding the 'tip': the last revision to be committed to this Branch.
158
(And the revno of that revision.)
159
* Knowing how to open the Repository that holds its history.
160
* Allowing write locks to be taken out to prevent concurrent alterations to the branch.
132
* Holding user preferences that are set in a Branch.
133
* Holding the 'tip': the last revision to be committed to this Branch. (And the revno of that revision.)
134
* Knowing how to open the Repository that holds its history.
135
* Allowing write locks to be taken out to prevent concurrent alterations to the branch.
164
* URL access to its base directory.
165
* A Transport to access its files.
166
* A Repository to hold its history.
138
* URL access to its base directory.
139
* A Transport to access its files.
140
* A Repository to hold its history.
173
146
and graph relationships between them. A repository holds a bag of
174
147
revision data that can be pointed to by various branches:
176
* Maintains storage of various history data at a URL:
178
* Revisions (Must have a matching inventory)
180
* Inventories for each Revision. (Must have all the file texts available).
183
* Synchronizes concurrent access to the repository by different
184
processes. (Most repository implementations use a physical mutex only
185
for a short period, and effectively support multiple readers and
149
* Maintains storage of various history data at a URL:
151
* Revisions (Must have a matching inventory)
153
* Inventories for each Revision. (Must have all the file texts available).
156
* Synchronizes concurrent access to the repository by different
157
processes. (Most repository implementations use a physical
158
mutex only for a short period, and effectively support multiple readers
188
161
Stacked Repositories
189
162
--------------------
212
185
server exposes the stacked-on URL and the client can open that.
218
This section describes the model for how bzr stores its data. The
219
representation of that data on disk varies considerable depending on the
220
format of the repository (and to a lesser extent the format of the branch
221
and working tree), but ultimately the set of objects being represented is
227
A branch directly contains:
229
* the ID of the current revision that branch (a.k.a. the “tip”)
230
* some settings for that branch (the values in “branch.conf”)
231
* the set of tags for that branch (not supported in all formats)
233
A branch implicitly references:
235
* A repository. The repository might be colocated in the same directory
236
as the branch, or it might be somewhere else entirely.
242
A repository contains:
249
A store is a key-value mapping. This says nothing about the layout on
250
disk, just that conceptually there are distinct stores, each with a
251
separate namespace for the keys. Internally the repository may serialize
252
stores in the same file, and/or e.g. apply compression algorithms that
253
combine records from separate stores in one block, etc.
255
You can consider the repository as a single key space, with keys that look
256
like *(store-name, ...)*. For example, *('revisions',
257
revision-id)* or *('texts', revision-id, file-id)*.
262
Stores revision objects. The keys are GUIDs. The value is a revision
263
object (the exact representation on disk depends on the repository
266
As described in `Core Concepts`_ a revision describes a snapshot of the
267
tree of files and some metadata about them.
271
* parent revisions (an ordered sequence of zero or more revision IDs)
275
* (and all other revision properties)
277
* an inventory ID (that inventory describes the tree contents). Is often
278
the same as the revision ID, but doesn't have to be (e.g. if no files
279
were changed between two revisions then both revisions will refer to
286
Stores inventory objects. The keys are GUIDs. (Footnote: there will
287
usually be a revision with the same key in the revision store, but there
288
are rare cases where this is not true.)
290
An inventory object contains:
292
* a set of inventory entries
294
An inventory entry has the following attributes
296
* a file-id (a GUID, or the special value TREE_ROOT for the root entry of
297
inventories created by older versions of bzr)
298
* a revision-id, a GUID (generally corresponding to the ID of a
299
revision). The combination of (file-id, revision-id) is a key into the
301
* a kind: one of file, directory, symlink, tree-reference (tree-reference
302
is only supported in unsupported developer formats)
303
* parent-id: the file-id of the directory that contains this entry (this
304
value is unset for the root of the tree).
305
* name: the name of the file/directory/etc in that parent directory
306
* executable: a flag indicating if the executable bit is set for that
309
An inventory entry will have other attributes, depending on the kind:
328
For some more details see `Inventories <inventory.html>`_.
334
Stores the contents of individual versions of files. The keys are pairs
335
of (file-id, revision-id), and the values are the full content (or
336
"text") of a version of a file.
338
For consistency/simplicity text records exist for all inventory entries,
339
but in general only entries with of kind "file" have interesting records.
345
Stores cryptographic signatures of revision contents. The keys match
346
those of the revision store.
348
.. _Core Concepts: http://doc.bazaar.canonical.com/latest/en/user-guide/core_concepts.html
351
189
vim: ft=rst tw=74 ai
added
removed
doc/developers/overview.txt
