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author Brian Neal <bgneal@gmail.com>
date Wed, 30 Nov 2011 18:26:09 -0600
parents f76e34af6e72
children 727c48601d66
rev   line source
bgneal@1 1 .. role:: strike
bgneal@1 2 :class: strike
bgneal@1 3
bgneal@0 4 Introduction to Distributed Version Control with Mercurial
bgneal@0 5 ==========================================================
bgneal@0 6
bgneal@0 7 ----
bgneal@0 8
bgneal@1 9 (Sublimal Message)
bgneal@1 10 ==================
bgneal@1 11
bgneal@4 12 .. image:: images/stop.jpg
bgneal@1 13
bgneal@1 14 ----
bgneal@1 15
bgneal@0 16 # whoami
bgneal@0 17 ========
bgneal@0 18
bgneal@0 19 Brian Neal <bgneal1@rockwellcollins.com>
bgneal@0 20
bgneal@0 21 Started at Rockwell Collins in July 1999
bgneal@0 22
bgneal@5 23 You might remember me from the following programs:
bgneal@0 24
bgneal@0 25 - UMS (July 1999 - Spring 2000)
bgneal@0 26 - Surgical Strike - (Spring - Fall 2000)
bgneal@0 27 - JTRS 2B - (Fall 2000 - Summer 2001)
bgneal@0 28 - SCAMP SEP - (Summer 2001 - October 2004)
bgneal@0 29 - TTNT (January 2005 - Present)
bgneal@0 30
bgneal@0 31 ----
bgneal@0 32
bgneal@0 33 Brief History of Version Control Tools
bgneal@0 34 ======================================
bgneal@0 35
bgneal@0 36 First Generation
bgneal@0 37 ----------------
bgneal@0 38
bgneal@1 39 - No networking!
bgneal@1 40 - Concurrency method: locks
bgneal@0 41 - Examples:
bgneal@0 42
bgneal@0 43 - SCCS - 1972
bgneal@0 44 - RCS - 1982
bgneal@0 45
bgneal@0 46 ----
bgneal@0 47
bgneal@0 48 Brief History of Version Control Tools
bgneal@0 49 ======================================
bgneal@0 50
bgneal@0 51 Second Generation
bgneal@0 52 -----------------
bgneal@0 53
bgneal@0 54 - Client/Server networking; CVCS (Centralized Version Control)
bgneal@1 55 - Concurrency method: merge before commit
bgneal@0 56 - Examples:
bgneal@0 57
bgneal@0 58 - CVS - 1990
bgneal@0 59 - IBM Rational ClearCase - 1992
bgneal@0 60 - Visual SourceSafe - 1994
bgneal@0 61 - Perforce - 1995
bgneal@0 62 - SVN - 2000
bgneal@0 63
bgneal@0 64 ----
bgneal@0 65
bgneal@0 66 Brief History of Version Control Tools
bgneal@0 67 ======================================
bgneal@0 68
bgneal@0 69 Third Generation
bgneal@0 70 ----------------
bgneal@0 71
bgneal@0 72 - Distributed networking; DVCS (Distributed Version Control)
bgneal@1 73 - Concurrency method: commit then merge
bgneal@1 74 - Examples:
bgneal@0 75
bgneal@0 76 - Bitkeeper - 2000
bgneal@0 77 - Darcs - 2003
bgneal@0 78 - Monotone - 2003
bgneal@0 79 - Git - 2005
bgneal@0 80 - **Mercurial** - 2005
bgneal@0 81 - Fossil - 2006
bgneal@0 82 - Bazaar - 2007
bgneal@1 83 - Veracity - 2011
bgneal@1 84
bgneal@1 85 ----
bgneal@1 86
bgneal@1 87 What is a CVCS Again?
bgneal@1 88 =====================
bgneal@1 89
bgneal@1 90 .. image:: images/cvcs.png
bgneal@1 91
bgneal@1 92 ----
bgneal@1 93
bgneal@2 94 So what's a DVCS look like?
bgneal@2 95 ===========================
bgneal@2 96
bgneal@2 97 .. image:: images/dvcs.png
bgneal@2 98
bgneal@2 99 All repositories are peers. By convention only, one repository is designated the master.
bgneal@6 100 It is possible for all peers to exchange changes (via *push* and *pull* operations).
bgneal@2 101
bgneal@2 102 ----
bgneal@2 103
bgneal@2 104 What does a DVCS buy you?
bgneal@2 105 =========================
bgneal@2 106
bgneal@2 107 - Private workspaces
bgneal@2 108 - Offline mode
bgneal@2 109 - Speed
bgneal@2 110 - Scalability
bgneal@2 111 - Split Geography
bgneal@2 112 - Flexible workflows
bgneal@2 113 - Distributed backups
bgneal@2 114 - **Easier merging**
bgneal@2 115 - **Commit before merge**
bgneal@2 116
bgneal@2 117 ----
bgneal@2 118
bgneal@2 119 Private Workspaces
bgneal@2 120 ==================
bgneal@2 121
bgneal@2 122 - You can safely experiment in your local repository
bgneal@2 123 - Commit as often as you like without affecting the team
bgneal@10 124
bgneal@10 125 - Encourages "micro-commits"
bgneal@10 126 - With SVN, people often hold back until an entire feature is complete
bgneal@10 127
bgneal@2 128 - Encourages experimentation
bgneal@2 129
bgneal@2 130 - Make cheap repository clones to try things out
bgneal@2 131 - Not visible to coworkers
bgneal@2 132
bgneal@2 133 ----
bgneal@2 134
bgneal@2 135 Offline Mode
bgneal@2 136 ============
bgneal@2 137
bgneal@2 138 - Work when you have spotty or no network access
bgneal@2 139 - Full access to the repo when offline
bgneal@2 140 - Can work on multiple tasks offline
bgneal@2 141
bgneal@2 142 - Work on bug report #1
bgneal@2 143 - Commit
bgneal@2 144 - Work on bug report #2
bgneal@2 145 - With a CVCS, you'd have both fixes in the same pending commit
bgneal@2 146
bgneal@2 147 ----
bgneal@2 148
bgneal@2 149 Speed
bgneal@2 150 =====
bgneal@2 151
bgneal@2 152 - Local operations are **fast**
bgneal@8 153
bgneal@8 154 - No, really, **you will** notice a big difference
bgneal@8 155 - Switching between branches will blow your mind
bgneal@8 156
bgneal@2 157 - Initial pull down of an entire repository *might* be slower than a CVCS
bgneal@2 158
bgneal@2 159 - Then again, you might be surprised
bgneal@2 160 - Mercurial, for example, stores an entire repository in less space than
bgneal@2 161 a SVN working copy in many cases
bgneal@8 162
bgneal@2 163
bgneal@2 164 ----
bgneal@2 165
bgneal@2 166 Scalability
bgneal@2 167 ===========
bgneal@2 168
bgneal@2 169 - Some CVCS systems require heavy weight hardware to support the server
bgneal@2 170
bgneal@2 171 - E.g. ClearCase with a thousand users
bgneal@2 172 - With a DVCS, only pushes & pulls contact a central server
bgneal@2 173 - Most of the work is done locally
bgneal@2 174
bgneal@2 175 ----
bgneal@2 176
bgneal@2 177 Split Geography
bgneal@2 178 ===============
bgneal@2 179
bgneal@6 180 - Imagine a team split between Cedar Rapids & Richardson...
bgneal@10 181 - With a CVCS, you have to pick where to put the server
bgneal@2 182 - The remote location is stuck with network latency & associated problems
bgneal@2 183 - With a DVCS, each site can have a central repository
bgneal@2 184
bgneal@2 185 - The two central repos can be synched when convenient or even scripted
bgneal@2 186
bgneal@9 187 .. image:: images/split_geography.png
bgneal@9 188
bgneal@2 189 ----
bgneal@2 190
bgneal@2 191 Flexible Workflows
bgneal@2 192 ==================
bgneal@2 193
bgneal@2 194 - There is no internal concept of a central repository
bgneal@2 195 - A central repository exits only by convention
bgneal@2 196 - More elaborate topologies and workflows can be created:
bgneal@2 197
bgneal@2 198 - A SW team may push to a central SW repo
bgneal@2 199 - Periodically changes from the SW repo are pushed to a QA repo
bgneal@2 200 - Changes from the QA repo can be pushed into a release repo
bgneal@9 201
bgneal@9 202 .. image:: images/flexible_workflows.png
bgneal@2 203
bgneal@2 204 ----
bgneal@2 205
bgneal@2 206 Distributed Backups
bgneal@2 207 ===================
bgneal@2 208
bgneal@2 209 - With a DVCS, multiple copies of the repository exist on multiple machines
bgneal@2 210 - **Of course, this is no substitute for a real backup strategy!**
bgneal@2 211 - But usually, and with short notice, you can easily designate a repository as
bgneal@2 212 the central repository in an emergency
bgneal@2 213
bgneal@2 214 ----
bgneal@2 215
bgneal@2 216 Easier Merging
bgneal@2 217 ==============
bgneal@2 218
bgneal@2 219 - Subversion has a bad reputation for merging
bgneal@2 220
bgneal@2 221 - Some of this is not warranted...
bgneal@2 222
bgneal@2 223 - Merge tracking was added in SVN v1.5
bgneal@2 224
bgneal@2 225 - SVN does not handle file renames and tree conflicts very well
bgneal@2 226 - A lot of teams simply avoid merging out of fear
bgneal@2 227
bgneal@2 228 ----
bgneal@2 229
bgneal@2 230 Easier Merging (cont.)
bgneal@2 231 ======================
bgneal@2 232
bgneal@2 233 - Why is merging better in a DVCS?
bgneal@2 234
bgneal@2 235 - Merging simply has to work correctly and be easy in a DVCS
bgneal@2 236
bgneal@2 237 - More attention was paid to this aspect by DVCS's
bgneal@2 238
bgneal@2 239 - DVCS's use directed acyclic graphs internally to represent change sets
bgneal@2 240
bgneal@2 241 - More information is available to make merge decisions
bgneal@2 242 - Easier to find common ancestors of code
bgneal@2 243
bgneal@2 244 - Developer changes and merge changes are separate
bgneal@2 245
bgneal@2 246 - "Commit before merge"
bgneal@2 247
bgneal@2 248 ----
bgneal@2 249
bgneal@2 250 Commit Before Merge
bgneal@2 251 ===================
bgneal@2 252
bgneal@2 253 - With a CVCS:
bgneal@2 254
bgneal@2 255 - You make changes in your working copy
bgneal@2 256 - Before you can commit, you often must peform an update
bgneal@2 257
bgneal@2 258 - This may trigger a merge
bgneal@2 259 - Your changes are now mixed up with your friendly coworkers' changes
bgneal@2 260 - Sometimes this can be a problem...
bgneal@2 261
bgneal@2 262 - With a DVCS:
bgneal@2 263
bgneal@2 264 - You make changes in your working copy
bgneal@3 265 - You commit locally!
bgneal@2 266 - You can then choose to pull changes from others and merge
bgneal@2 267
bgneal@2 268 - **Your changes are already safely tucked away and can be retrieved later if things go wrong**
bgneal@2 269
bgneal@2 270 ----
bgneal@2 271
bgneal@2 272 Okay, what's the catch?
bgneal@2 273 =======================
bgneal@2 274
bgneal@2 275 Potential drawbacks to a DVCS
bgneal@2 276 -----------------------------
bgneal@2 277
bgneal@2 278 - Practically no support for locks
bgneal@2 279
bgneal@2 280 - This makes working with binary files difficult in a team environment
bgneal@2 281
bgneal@2 282 - Huge repositories are not practical
bgneal@2 283
bgneal@2 284 - Hetrogenous repositories are not practical
bgneal@2 285
bgneal@2 286 - Not a good idea to mix, say, software, systems, and firmware in the same repo
bgneal@2 287 - Not a good idea to mix multiple products in the same repo
bgneal@2 288 - Arguably, this applies to a CVCS as well
bgneal@2 289
bgneal@7 290 - No support for path-based access control
bgneal@7 291
bgneal@7 292 - With current tools, you either can access the full repo, or nothing
bgneal@7 293
bgneal@2 294 ----
bgneal@2 295
bgneal@2 296 Introduction to Mercurial
bgneal@2 297 =========================
bgneal@2 298
bgneal@5 299 - Overview
bgneal@6 300 - Repositories & working directories
bgneal@2 301 - Changesets
bgneal@4 302 - Branches & Tags
bgneal@4 303 - Example workflow
bgneal@3 304 - Command overview
bgneal@2 305
bgneal@2 306 ----
bgneal@2 307
bgneal@5 308 Mercurial Overview
bgneal@5 309 ==================
bgneal@5 310
bgneal@5 311 - Distributed Version Control System
bgneal@5 312 - Free, open source software licensed under GPL Version 2
bgneal@5 313 - Available for Microsoft Windows, GNU/Linux, Mac OS X, Solaris 11 Express
bgneal@5 314 - Written in Python with a small amount of C
bgneal@5 315 - Extensible with official and 3rd party extensions
bgneal@5 316 - TortoiseHg is a popular GUI for Windows
bgneal@5 317 - Reputation for being fast & easy to get started with
bgneal@5 318 - Can be served via Apache Web server
bgneal@5 319 - Repository hooks
bgneal@5 320 - Integrates with Trac
bgneal@5 321 - Can import history from other tools, including Subversion
bgneal@5 322
bgneal@5 323 ----
bgneal@5 324
bgneal@6 325 Repositories & Working Directories
bgneal@6 326 ==================================
bgneal@3 327
bgneal@3 328 A repository consists of two things:
bgneal@3 329
bgneal@4 330 - Your working directory (similar to a working copy in SVN)
bgneal@3 331 - The repository itself (also known as "the store")
bgneal@3 332
bgneal@3 333 - A .hg directory at the top of your working copy
bgneal@3 334
bgneal@3 335 Example::
bgneal@3 336
bgneal@4 337 $ ls -A
bgneal@3 338 .hg .hgignore images/ slides.cfg slides.css slides.html slides.rst
bgneal@3 339
bgneal@6 340 - Repositories communicate via the *push* and *pull* commands
bgneal@6 341
bgneal@6 342 - Push & Pull do not affect your working directory
bgneal@6 343
bgneal@6 344 - An *update* or *merge* must be performed to receive remote changes into your working directory
bgneal@6 345
bgneal@3 346 ----
bgneal@3 347
bgneal@3 348 What's in a Repository?
bgneal@3 349 =======================
bgneal@3 350
bgneal@3 351 A repository consists of a directed, acyclic graph of *changesets*
bgneal@3 352
bgneal@3 353 .. image:: images/repos.png
bgneal@3 354
bgneal@4 355 - Each changeset can have 0, 1, or 2 parents (and infinite children)
bgneal@3 356 - A changeset with 0 parents is the root
bgneal@3 357 - A changeset with 2 parents is the result of a merge
bgneal@4 358 - The newest changeset is called the *tip*, a special tag name
bgneal@4 359
bgneal@4 360 ----
bgneal@4 361
bgneal@4 362 What's a Changeset?
bgneal@4 363 ===================
bgneal@4 364
bgneal@4 365 A changeset is an atomic collection of changes and some meta information.
bgneal@4 366 The meta information includes:
bgneal@4 367
bgneal@4 368 - Who made the changes
bgneal@4 369 - When the changes were made
bgneal@4 370 - Why - the commit message
bgneal@4 371 - The name of the branch the changes were made on ("default" is the default)
bgneal@4 372 - A local revision number
bgneal@4 373 - A changeset ID; a 40 digit hex number (SHA-1 hash of the changeset & parents)
bgneal@4 374
bgneal@4 375 A changeset can be named by:
bgneal@4 376
bgneal@4 377 - Revision number (within a repository)
bgneal@4 378 - Changeset ID (globally)
bgneal@4 379 - Tag name
bgneal@4 380
bgneal@4 381 ----
bgneal@4 382
bgneal@4 383 Branches & Tags
bgneal@4 384 ===============
bgneal@4 385
bgneal@4 386 - In the simple case, each changeset appear in a line
bgneal@4 387 - When a changeset develops 2 or more children, a branch occurs
bgneal@4 388
bgneal@4 389 - The latest revision of a branch is called a *head*
bgneal@4 390 - A *merge* is when two branches join back together
bgneal@4 391 - Branches can be given names; the default branch name is *"default"*
bgneal@4 392
bgneal@4 393 - Changesets can be given human readable names, or *tags*
bgneal@4 394
bgneal@4 395 - *Local tags* are only visible within a repository
bgneal@4 396 - *Regular tags* are revision controlled and propagate to other repos
bgneal@4 397 - The newest head in a repository is a tag called *tip*
bgneal@4 398
bgneal@4 399 ----
bgneal@4 400
bgneal@4 401 Example Workflow
bgneal@4 402 ================
bgneal@4 403
bgneal@4 404 .. image:: images/workflow1.png
bgneal@4 405
bgneal@4 406 ----
bgneal@4 407
bgneal@4 408 Example Workflow (cont.)
bgneal@4 409 ========================
bgneal@4 410
bgneal@4 411 .. image:: images/workflow2.png
bgneal@4 412
bgneal@4 413 ----
bgneal@4 414
bgneal@4 415 Example Workflow (cont.)
bgneal@4 416 ========================
bgneal@4 417
bgneal@4 418 .. image:: images/workflow3.png
bgneal@3 419
bgneal@6 420 - Notice that after Alice's pull:
bgneal@6 421
bgneal@6 422 - Her working directory is unaffected
bgneal@6 423 - Her repository only has one head => no merging required
bgneal@6 424
bgneal@6 425
bgneal@3 426 ----
bgneal@3 427
bgneal@3 428 SVN Commands for Review
bgneal@3 429 =======================
bgneal@1 430
bgneal@1 431 Basic SVN commands:
bgneal@1 432
bgneal@1 433 - add, remove, copy, move, mkdir
bgneal@1 434 - checkout, commit, update, revert
bgneal@1 435 - merge, resolved, diff
bgneal@4 436 - status, log
bgneal@1 437 - lock, unlock
bgneal@1 438
bgneal@1 439 ----
bgneal@1 440
bgneal@4 441 Basic Mercurial Commands
bgneal@4 442 ========================
bgneal@1 443
bgneal@1 444 Mercurial (hg) vs SVN commands:
bgneal@1 445
bgneal@1 446 - add, remove, copy, move, :strike:`mkdir`
bgneal@1 447 - :strike:`checkout`, commit, update, revert
bgneal@4 448 - merge, resolve, diff, **heads**
bgneal@4 449 - status, log
bgneal@1 450 - :strike:`lock, unlock`
bgneal@1 451
bgneal@1 452 Additional "distributed commands":
bgneal@1 453
bgneal@5 454 - **clone**, **push**, **pull**
bgneal@5 455 - **incoming**, **outgoing**
bgneal@1 456
bgneal@4 457 **Not a whole lot to learn above SVN**
bgneal@4 458
bgneal@4 459 ----
bgneal@4 460
bgneal@4 461 References
bgneal@4 462 ==========
bgneal@4 463
bgneal@4 464 - Mercurial http://mercurial.selenic.com/
bgneal@4 465 - Mercurial Wiki http://mercurial.selenic.com/wiki/
bgneal@4 466 - Mercurial Book (free!) http://hgbook.red-bean.com/
bgneal@4 467 - Hg Init: A Mercurial Tutorial http://hginit.com
bgneal@4 468 - Version Control By Example (free!) http://www.ericsink.com/vcbe/
bgneal@4 469
bgneal@5 470 This presentation is available at::
bgneal@5 471
bgneal@5 472 $ hg clone https://bitbucket.org/bgneal/dvcs_intro_brownbag
bgneal@5 473
bgneal@4 474 ----
bgneal@4 475
bgneal@4 476 Questions?
bgneal@4 477 ==========
bgneal@4 478