1 \chapter{Introduction}

2 \label{chap:intro}

3

4 \section{A propros de la gestion source}

5

6 La gestion de source est un processus permettant de gérer différentes

7 version de la même information. Dans sa forme la plus simple, c'est

8 quelquechose que tout le monde fait manuellement : quand vous modifiez

9 un fichier, vous le sauvegarder sous un nouveau nom contenant un numéro,

10 à chaque fois plus grand la précédente version.

11

12 Ce genre de gestion de version manuel est cependant sujette facilement

13 à des erreurs, ainsi, depuis longtemps, des logiciels existent pour

14 adresser cette problématique. Les premiers outils de gestion de source

15 étaient destinés à aider un seul utilisateur, à automatiser la gestion

16 des versions d'un seulf fichier. Dans les dernières décades, cette cilble

17 a largement était agrandie, ils gèrent désormais de multiple fichiers, et

18 aident un grand nombre de personnes à travailler ensemble. Le outils les

19 plus modernes n'ont aucune difficultés à gérer plusieurs milliers de

20 personnes travaillant ensemble sur des projets regroupant plusieurs

21 centaines de milliers de fichiers.

22

23 \subsection{Pourquoi utiliser un gestionnaire de source ?}

24

25 Il y a de nombreuse raisons pour que vous ou votre équipe souhaitiez

26 utiliser un outil automatisant la gestion de version pour votre projet.

27 \begin{itemize}

28 \item L'outil se chargera de suivre l'évolution de votre projet, sans

29 que vous ayez à le faire. Pour chaque modification, vous aurez à votre

30 disposition un journal indiquant \emph{qui} a faient quoi, \emph{pourquoi}

31 ils l'ont fait, \emph{quand} ils l'ont fait, et \emph{ce} qu'ils ont

32 modifiés.

33 \item Quand vous travaillez avec d'autres personnes, les logiciels de

34 gestion de source facilite le travail collaboratif. Par exemple, quand

35 plusieurs personnes font, plus ou moins simultannéement, des modifications

36 incompatibles, le logiciel vous aidera à identifier et résoudre les conflits.

37 \item L'outil vous aidera à réparer vos erreurs. Si vous effectuez un changement

38 qui se révèlera être une erreur, vous pourrez revenir fiablement à une version

39 antérieur d'une fichier ou même d'un ensemble de fichier. En fait, un outil de

40 gestion de source \emph{vraiment} efficace vous permettra d'identifier à quel

41 moment le problème est apparu (voir la section~\ref{sec:undo:bisect} pour plus

42 de détails).

43 \item L'outil vous permettra aussi de travailler sur plusieurs versions différentes

44 de votre projet et à gérer l'écart entre chaque.

45 \end{itemize}

46 La plupart de ces raisons ont autant d'importances---du moins en théorie--- que

47 vous travailliez sur un projet pour vous, ou avec une centaine d'autres

48 personnes.

49

50 Une question fondamental à propos des outils de gestion de source, qu'il s'agisse

51 du projet d'une personne ou d'une grande équipe, est quelles sont ses

52 \emph{avantages} par rapport à ses \emph{coût}. Un outil qui est difficile à

53 utiliser ou à comprendre exigera un effort d'adoption.

54

55 Un projet de cinq milles personnnes s'effondrera très certainement de lui même

56 sans aucun processus et outil de gestion de source. Dans ce cas, le coût

57 d'utilisation d'un logiciel de gestion de source est dérisoire, puisque

58 \emph{sans}, l'échec est presque garanti.

59

60 D'un autre coté, un ``rapide hack'' d'une personnne peut sembler un contexte

61 bien pauvre pour utiliser un outil de gestion de source, car, bien évidement

62 le coût d'utilisation dépasse le coût total du projet. N'est ce pas ?

63

64 Mercurial supporte ces \emph{deux} échelles de travail. Vous pouvez apprendre

65 les bases en juste quelques minutes, et, grâce à sa performance, vous pouvez

66 l'utiliser avec facilité sur le plus petit des projets. Cette simplicité

67 signifie que vous n'avez pas de concepts obscures ou de séquence de commandes

68 défiant l'imagination, complètement décorrelé de \emph{ce que vous êtes

69 vraiment entrain de faire}. En même temps, ces mêmes performances et sa

70 nature ``peer-to-peer'' vous permet d'augmenter, sans difficulté, son

71 utilisation à de très grand projet.

72

73 Aucun outil de gestion de source ne peut sauver un projet mal mené, mais un

74 bon outil peut faire une grande différence dans la fluidité avec lequel

75 vous pourrez travailler avec.

76

77 \subsection{Les multiples noms de la gestion de source}

78

79 La gestion de source est un domaine divers, tellement qu'il n'existe pas

80 une seul nom ou acronyme pour le désigner. Voilà quelqu'uns des noms ou

81 acronymes que vous rencontrerez le plus souvent:

82 \begin{itemize}

83 \item \textit{Revision control (RCS)} ;

84 \item Software configuration management (SCM), ou \textit{configuration management} ;

85 \item \textit{Source code management} ;

86 \item \textit{Source code control}, ou \textit{source control} ;

87 \item \textit{Version control (VCS)}.

88 \end{itemize}

89

90 \notebox {

91 Note du traducteur : J'ai conservé la liste des noms en anglais pour des raisons de commodité (ils sont plus ``googelable''). J'ai choisi de conserver le terme ``gestion de sources'' comme traduction unique dans l'ensemble du document.

92

93 En outre, j'ai opté pour conserver l'ensemble des opérations de Mercurial (commit, push, pull,...) en anglais, là aussi pour faciliter la lecture d'autres documents en anglais, et

94 aussi son utilisation.

95 }

96

97 Certains personnes prétendent que ces termes ont en fait des sens

98 différents mais en pratique ils se recouvrent tellement qu'il n'y a pas

99 réellement de manière pertinente de les distinguer.

100

101 \section{Une courte histoire de la gestion de source}

102

103 Le plus célèbre des anciens outils de gestion de source est \textit{SCCS (Source

104 Code Control System)}, que Marc Rochkind conçu dans les laboratoire de recherche de Bell

105 (\textit{Bell Labs}), dans le début des années 70. \textit{SCCS} ne fonctionner que sur des fichiers individuels, et demandait à personne travaillant sur le projet d'avoir un accès à un répertoire de travail commun, sur un unique système.

106 Seulement une personne pouvait modifier un fichier au même moment, ce fonctionnement était assuré par l'utilisation de verrou (``lock''). Il était courant que des personnes ne vérouille

107 des fichiers, et plus tard, oublie de le dévérouiller; empêchant n'importe qui d'autre de

108 travailler sur ces fichiers sans l'aide de l'administrateur...

109

110 Walter Tichy a développé une alternative libre à \textit{SCCS} au début des années 80, qu'il

111 nomma \textit{RSC (Revison Control System)}. Comme \textit{SCCS}, \textit{RCS}

112 demander aux développeurs de travailler sur le même répertoire partagé, et de vérouiller les

113 fichiers pour se prémunir de tout conflit issue de modifications concurrentes.

114

115 Un peu plus tard dans les années 1980, Dick Grune utilisa \textit{RCS} comme une brique de base pour un ensemble de scripts \textit{shell} qu'il intitula cmt, avant de la renommer en \textit{CVS (Concurrent Versions System)}. La grande innovation de CVS était que les développeurs pouvaient travailler simultanéement and indépendament dans leur propre espace de travail. Ces espaces de travail privés assuraient que les développeurs ne se marche mutuellement sur les pieds, comme c'était souvent le cas avec RCS et SCCS. Chaque développeur disposait donc de sa copie de tout les fichiers du projet, et ils pouvaient donc librement les modifier. Ils devaient néanmoins effectuer la ``fusion'' (\textit{``merge''}) de leur fichiers, avant d'effectuer le ``commit'' de leur modification sur le dépôt central.

116

117 Brian Berliner took Grune's original scripts and rewrote them in~C,

118 releasing in 1989 the code that has since developed into the modern

119 version of CVS. CVS subsequently acquired the ability to operate over

120 a network connection, giving it a client/server architecture. CVS's

121 architecture is centralised; only the server has a copy of the history

122 of the project. Client workspaces just contain copies of recent

123 versions of the project's files, and a little metadata to tell them

124 where the server is. CVS has been enormously successful; it is

125 probably the world's most widely used revision control system.

126

127 In the early 1990s, Sun Microsystems developed an early distributed

128 revision control system, called TeamWare. A TeamWare workspace

129 contains a complete copy of the project's history. TeamWare has no

130 notion of a central repository. (CVS relied upon RCS for its history

131 storage; TeamWare used SCCS.)

132

133 As the 1990s progressed, awareness grew of a number of problems with

134 CVS. It records simultaneous changes to multiple files individually,

135 instead of grouping them together as a single logically atomic

136 operation. It does not manage its file hierarchy well; it is easy to

137 make a mess of a repository by renaming files and directories. Worse,

138 its source code is difficult to read and maintain, which made the

139 ``pain level'' of fixing these architectural problems prohibitive.

140

141 In 2001, Jim Blandy and Karl Fogel, two developers who had worked on

142 CVS, started a project to replace it with a tool that would have a

143 better architecture and cleaner code. The result, Subversion, does

144 not stray from CVS's centralised client/server model, but it adds

145 multi-file atomic commits, better namespace management, and a number

146 of other features that make it a generally better tool than CVS.

147 Since its initial release, it has rapidly grown in popularity.

148

149 More or less simultaneously, Graydon Hoare began working on an

150 ambitious distributed revision control system that he named Monotone.

151 While Monotone addresses many of CVS's design flaws and has a

152 peer-to-peer architecture, it goes beyond earlier (and subsequent)

153 revision control tools in a number of innovative ways. It uses

154 cryptographic hashes as identifiers, and has an integral notion of

155 ``trust'' for code from different sources.

156

157 Mercurial began life in 2005. While a few aspects of its design are

158 influenced by Monotone, Mercurial focuses on ease of use, high

159 performance, and scalability to very large projects.

160

161 \section{Trends in revision control}

162

163 There has been an unmistakable trend in the development and use of

164 revision control tools over the past four decades, as people have

165 become familiar with the capabilities of their tools and constrained

166 by their limitations.

167

168 The first generation began by managing single files on individual

169 computers. Although these tools represented a huge advance over

170 ad-hoc manual revision control, their locking model and reliance on a

171 single computer limited them to small, tightly-knit teams.

172

173 The second generation loosened these constraints by moving to

174 network-centered architectures, and managing entire projects at a

175 time. As projects grew larger, they ran into new problems. With

176 clients needing to talk to servers very frequently, server scaling

177 became an issue for large projects. An unreliable network connection

178 could prevent remote users from being able to talk to the server at

179 all. As open source projects started making read-only access

180 available anonymously to anyone, people without commit privileges

181 found that they could not use the tools to interact with a project in

182 a natural way, as they could not record their changes.

183

184 The current generation of revision control tools is peer-to-peer in

185 nature. All of these systems have dropped the dependency on a single

186 central server, and allow people to distribute their revision control

187 data to where it's actually needed. Collaboration over the Internet

188 has moved from constrained by technology to a matter of choice and

189 consensus. Modern tools can operate offline indefinitely and

190 autonomously, with a network connection only needed when syncing

191 changes with another repository.

192

193 \section{A few of the advantages of distributed revision control}

194

195 Even though distributed revision control tools have for several years

196 been as robust and usable as their previous-generation counterparts,

197 people using older tools have not yet necessarily woken up to their

198 advantages. There are a number of ways in which distributed tools

199 shine relative to centralised ones.

200

201 For an individual developer, distributed tools are almost always much

202 faster than centralised tools. This is for a simple reason: a

203 centralised tool needs to talk over the network for many common

204 operations, because most metadata is stored in a single copy on the

205 central server. A distributed tool stores all of its metadata

206 locally. All else being equal, talking over the network adds overhead

207 to a centralised tool. Don't underestimate the value of a snappy,

208 responsive tool: you're going to spend a lot of time interacting with

209 your revision control software.

210

211 Distributed tools are indifferent to the vagaries of your server

212 infrastructure, again because they replicate metadata to so many

213 locations. If you use a centralised system and your server catches

214 fire, you'd better hope that your backup media are reliable, and that

215 your last backup was recent and actually worked. With a distributed

216 tool, you have many backups available on every contributor's computer.

217

218 The reliability of your network will affect distributed tools far less

219 than it will centralised tools. You can't even use a centralised tool

220 without a network connection, except for a few highly constrained

221 commands. With a distributed tool, if your network connection goes

222 down while you're working, you may not even notice. The only thing

223 you won't be able to do is talk to repositories on other computers,

224 something that is relatively rare compared with local operations. If

225 you have a far-flung team of collaborators, this may be significant.

226

227 \subsection{Advantages for open source projects}

228

229 If you take a shine to an open source project and decide that you

230 would like to start hacking on it, and that project uses a distributed

231 revision control tool, you are at once a peer with the people who

232 consider themselves the ``core'' of that project. If they publish

233 their repositories, you can immediately copy their project history,

234 start making changes, and record your work, using the same tools in

235 the same ways as insiders. By contrast, with a centralised tool, you

236 must use the software in a ``read only'' mode unless someone grants

237 you permission to commit changes to their central server. Until then,

238 you won't be able to record changes, and your local modifications will

239 be at risk of corruption any time you try to update your client's view

240 of the repository.

241

242 \subsubsection{The forking non-problem}

243

244 It has been suggested that distributed revision control tools pose

245 some sort of risk to open source projects because they make it easy to

246 ``fork'' the development of a project. A fork happens when there are

247 differences in opinion or attitude between groups of developers that

248 cause them to decide that they can't work together any longer. Each

249 side takes a more or less complete copy of the project's source code,

250 and goes off in its own direction.

251

252 Sometimes the camps in a fork decide to reconcile their differences.

253 With a centralised revision control system, the \emph{technical}

254 process of reconciliation is painful, and has to be performed largely

255 by hand. You have to decide whose revision history is going to

256 ``win'', and graft the other team's changes into the tree somehow.

257 This usually loses some or all of one side's revision history.

258

259 What distributed tools do with respect to forking is they make forking

260 the \emph{only} way to develop a project. Every single change that

261 you make is potentially a fork point. The great strength of this

262 approach is that a distributed revision control tool has to be really

263 good at \emph{merging} forks, because forks are absolutely

264 fundamental: they happen all the time.

265

266 If every piece of work that everybody does, all the time, is framed in

267 terms of forking and merging, then what the open source world refers

268 to as a ``fork'' becomes \emph{purely} a social issue. If anything,

269 distributed tools \emph{lower} the likelihood of a fork:

270 \begin{itemize}

271 \item They eliminate the social distinction that centralised tools

272 impose: that between insiders (people with commit access) and

273 outsiders (people without).

274 \item They make it easier to reconcile after a social fork, because

275 all that's involved from the perspective of the revision control

276 software is just another merge.

277 \end{itemize}

278

279 Some people resist distributed tools because they want to retain tight

280 control over their projects, and they believe that centralised tools

281 give them this control. However, if you're of this belief, and you

282 publish your CVS or Subversion repositories publically, there are

283 plenty of tools available that can pull out your entire project's

284 history (albeit slowly) and recreate it somewhere that you don't

285 control. So while your control in this case is illusory, you are

286 forgoing the ability to fluidly collaborate with whatever people feel

287 compelled to mirror and fork your history.

288

289 \subsection{Advantages for commercial projects}

290

291 Many commercial projects are undertaken by teams that are scattered

292 across the globe. Contributors who are far from a central server will

293 see slower command execution and perhaps less reliability. Commercial

294 revision control systems attempt to ameliorate these problems with

295 remote-site replication add-ons that are typically expensive to buy

296 and cantankerous to administer. A distributed system doesn't suffer

297 from these problems in the first place. Better yet, you can easily

298 set up multiple authoritative servers, say one per site, so that

299 there's no redundant communication between repositories over expensive

300 long-haul network links.

301

302 Centralised revision control systems tend to have relatively low

303 scalability. It's not unusual for an expensive centralised system to

304 fall over under the combined load of just a few dozen concurrent

305 users. Once again, the typical response tends to be an expensive and

306 clunky replication facility. Since the load on a central server---if

307 you have one at all---is many times lower with a distributed

308 tool (because all of the data is replicated everywhere), a single

309 cheap server can handle the needs of a much larger team, and

310 replication to balance load becomes a simple matter of scripting.

311

312 If you have an employee in the field, troubleshooting a problem at a

313 customer's site, they'll benefit from distributed revision control.

314 The tool will let them generate custom builds, try different fixes in

315 isolation from each other, and search efficiently through history for

316 the sources of bugs and regressions in the customer's environment, all

317 without needing to connect to your company's network.

318

319 \section{Why choose Mercurial?}

320

321 Mercurial has a unique set of properties that make it a particularly

322 good choice as a revision control system.

323 \begin{itemize}

324 \item It is easy to learn and use.

325 \item It is lightweight.

326 \item It scales excellently.

327 \item It is easy to customise.

328 \end{itemize}

329

330 If you are at all familiar with revision control systems, you should

331 be able to get up and running with Mercurial in less than five

332 minutes. Even if not, it will take no more than a few minutes

333 longer. Mercurial's command and feature sets are generally uniform

334 and consistent, so you can keep track of a few general rules instead

335 of a host of exceptions.

336

337 On a small project, you can start working with Mercurial in moments.

338 Creating new changes and branches; transferring changes around

339 (whether locally or over a network); and history and status operations

340 are all fast. Mercurial attempts to stay nimble and largely out of

341 your way by combining low cognitive overhead with blazingly fast

342 operations.

343

344 The usefulness of Mercurial is not limited to small projects: it is

345 used by projects with hundreds to thousands of contributors, each

346 containing tens of thousands of files and hundreds of megabytes of

347 source code.

348

349 If the core functionality of Mercurial is not enough for you, it's

350 easy to build on. Mercurial is well suited to scripting tasks, and

351 its clean internals and implementation in Python make it easy to add

352 features in the form of extensions. There are a number of popular and

353 useful extensions already available, ranging from helping to identify

354 bugs to improving performance.

355

356 \section{Mercurial compared with other tools}

357

358 Before you read on, please understand that this section necessarily

359 reflects my own experiences, interests, and (dare I say it) biases. I

360 have used every one of the revision control tools listed below, in

361 most cases for several years at a time.

362

363

364 \subsection{Subversion}

365

366 Subversion is a popular revision control tool, developed to replace

367 CVS. It has a centralised client/server architecture.

368

369 Subversion and Mercurial have similarly named commands for performing

370 the same operations, so if you're familiar with one, it is easy to

371 learn to use the other. Both tools are portable to all popular

372 operating systems.

373

374 Prior to version 1.5, Subversion had no useful support for merges.

375 At the time of writing, its merge tracking capability is new, and known to be

376 \href{http://svnbook.red-bean.com/nightly/en/svn.branchmerge.advanced.html#svn.branchmerge.advanced.finalword}{complicated

377 and buggy}.

378

379 Mercurial has a substantial performance advantage over Subversion on

380 every revision control operation I have benchmarked. I have measured

381 its advantage as ranging from a factor of two to a factor of six when

382 compared with Subversion~1.4.3's \emph{ra\_local} file store, which is

383 the fastest access method available. In more realistic deployments

384 involving a network-based store, Subversion will be at a substantially

385 larger disadvantage. Because many Subversion commands must talk to

386 the server and Subversion does not have useful replication facilities,

387 server capacity and network bandwidth become bottlenecks for modestly

388 large projects.

389

390 Additionally, Subversion incurs substantial storage overhead to avoid

391 network transactions for a few common operations, such as finding

392 modified files (\texttt{status}) and displaying modifications against

393 the current revision (\texttt{diff}). As a result, a Subversion

394 working copy is often the same size as, or larger than, a Mercurial

395 repository and working directory, even though the Mercurial repository

396 contains a complete history of the project.

397

398 Subversion is widely supported by third party tools. Mercurial

399 currently lags considerably in this area. This gap is closing,

400 however, and indeed some of Mercurial's GUI tools now outshine their

401 Subversion equivalents. Like Mercurial, Subversion has an excellent

402 user manual.

403

404 Because Subversion doesn't store revision history on the client, it is

405 well suited to managing projects that deal with lots of large, opaque

406 binary files. If you check in fifty revisions to an incompressible

407 10MB file, Subversion's client-side space usage stays constant The

408 space used by any distributed SCM will grow rapidly in proportion to

409 the number of revisions, because the differences between each revision

410 are large.

411

412 In addition, it's often difficult or, more usually, impossible to

413 merge different versions of a binary file. Subversion's ability to

414 let a user lock a file, so that they temporarily have the exclusive

415 right to commit changes to it, can be a significant advantage to a

416 project where binary files are widely used.

417

418 Mercurial can import revision history from a Subversion repository.

419 It can also export revision history to a Subversion repository. This

420 makes it easy to ``test the waters'' and use Mercurial and Subversion

421 in parallel before deciding to switch. History conversion is

422 incremental, so you can perform an initial conversion, then small

423 additional conversions afterwards to bring in new changes.

424

425

426 \subsection{Git}

427

428 Git is a distributed revision control tool that was developed for

429 managing the Linux kernel source tree. Like Mercurial, its early

430 design was somewhat influenced by Monotone.

431

432 Git has a very large command set, with version~1.5.0 providing~139

433 individual commands. It has something of a reputation for being

434 difficult to learn. Compared to Git, Mercurial has a strong focus on

435 simplicity.

436

437 In terms of performance, Git is extremely fast. In several cases, it

438 is faster than Mercurial, at least on Linux, while Mercurial performs

439 better on other operations. However, on Windows, the performance and

440 general level of support that Git provides is, at the time of writing,

441 far behind that of Mercurial.

442

443 While a Mercurial repository needs no maintenance, a Git repository

444 requires frequent manual ``repacks'' of its metadata. Without these,

445 performance degrades, while space usage grows rapidly. A server that

446 contains many Git repositories that are not rigorously and frequently

447 repacked will become heavily disk-bound during backups, and there have

448 been instances of daily backups taking far longer than~24 hours as a

449 result. A freshly packed Git repository is slightly smaller than a

450 Mercurial repository, but an unpacked repository is several orders of

451 magnitude larger.

452

453 The core of Git is written in C. Many Git commands are implemented as

454 shell or Perl scripts, and the quality of these scripts varies widely.

455 I have encountered several instances where scripts charged along

456 blindly in the presence of errors that should have been fatal.

457

458 Mercurial can import revision history from a Git repository.

459

460

461 \subsection{CVS}

462

463 CVS is probably the most widely used revision control tool in the

464 world. Due to its age and internal untidiness, it has been only

465 lightly maintained for many years.

466

467 It has a centralised client/server architecture. It does not group

468 related file changes into atomic commits, making it easy for people to

469 ``break the build'': one person can successfully commit part of a

470 change and then be blocked by the need for a merge, causing other

471 people to see only a portion of the work they intended to do. This

472 also affects how you work with project history. If you want to see

473 all of the modifications someone made as part of a task, you will need

474 to manually inspect the descriptions and timestamps of the changes

475 made to each file involved (if you even know what those files were).

476

477 CVS has a muddled notion of tags and branches that I will not attempt

478 to even describe. It does not support renaming of files or

479 directories well, making it easy to corrupt a repository. It has

480 almost no internal consistency checking capabilities, so it is usually

481 not even possible to tell whether or how a repository is corrupt. I

482 would not recommend CVS for any project, existing or new.

483

484 Mercurial can import CVS revision history. However, there are a few

485 caveats that apply; these are true of every other revision control

486 tool's CVS importer, too. Due to CVS's lack of atomic changes and

487 unversioned filesystem hierarchy, it is not possible to reconstruct

488 CVS history completely accurately; some guesswork is involved, and

489 renames will usually not show up. Because a lot of advanced CVS

490 administration has to be done by hand and is hence error-prone, it's

491 common for CVS importers to run into multiple problems with corrupted

492 repositories (completely bogus revision timestamps and files that have

493 remained locked for over a decade are just two of the less interesting

494 problems I can recall from personal experience).

495

496 Mercurial can import revision history from a CVS repository.

497

498

499 \subsection{Commercial tools}

500

501 Perforce has a centralised client/server architecture, with no

502 client-side caching of any data. Unlike modern revision control

503 tools, Perforce requires that a user run a command to inform the

504 server about every file they intend to edit.

505

506 The performance of Perforce is quite good for small teams, but it

507 falls off rapidly as the number of users grows beyond a few dozen.

508 Modestly large Perforce installations require the deployment of

509 proxies to cope with the load their users generate.

510

511

512 \subsection{Choosing a revision control tool}

513

514 With the exception of CVS, all of the tools listed above have unique

515 strengths that suit them to particular styles of work. There is no

516 single revision control tool that is best in all situations.

517

518 As an example, Subversion is a good choice for working with frequently

519 edited binary files, due to its centralised nature and support for

520 file locking.

521

522 I personally find Mercurial's properties of simplicity, performance,

523 and good merge support to be a compelling combination that has served

524 me well for several years.

525

526

527 \section{Switching from another tool to Mercurial}

528

529 Mercurial is bundled with an extension named \hgext{convert}, which

530 can incrementally import revision history from several other revision

531 control tools. By ``incremental'', I mean that you can convert all of

532 a project's history to date in one go, then rerun the conversion later

533 to obtain new changes that happened after the initial conversion.

534

535 The revision control tools supported by \hgext{convert} are as

536 follows:

537 \begin{itemize}

538 \item Subversion

539 \item CVS

540 \item Git

541 \item Darcs

542 \end{itemize}

543

544 In addition, \hgext{convert} can export changes from Mercurial to

545 Subversion. This makes it possible to try Subversion and Mercurial in

546 parallel before committing to a switchover, without risking the loss

547 of any work.

548

549 The \hgxcmd{conver}{convert} command is easy to use. Simply point it

550 at the path or URL of the source repository, optionally give it the

551 name of the destination repository, and it will start working. After

552 the initial conversion, just run the same command again to import new

553 changes.

554

555

556 %%% Local Variables:

557 %%% mode: latex

558 %%% TeX-master: "00book"

559 %%% End: