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Added a drawback about path-based access control.
author Brian Neal <bgneal@gmail.com>
date Sun, 13 Nov 2011 16:49:51 -0600
parents bcc4d16e03e8
children 1f58f03815f9
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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@2 124 - Encourages experimentation
bgneal@2 125
bgneal@2 126 - Make cheap repository clones to try things out
bgneal@2 127 - Not visible to coworkers
bgneal@2 128
bgneal@2 129 ----
bgneal@2 130
bgneal@2 131 Offline Mode
bgneal@2 132 ============
bgneal@2 133
bgneal@2 134 - Work when you have spotty or no network access
bgneal@2 135 - Full access to the repo when offline
bgneal@2 136 - Can work on multiple tasks offline
bgneal@2 137
bgneal@2 138 - Work on bug report #1
bgneal@2 139 - Commit
bgneal@2 140 - Work on bug report #2
bgneal@2 141 - With a CVCS, you'd have both fixes in the same pending commit
bgneal@2 142
bgneal@2 143 ----
bgneal@2 144
bgneal@2 145 Speed
bgneal@2 146 =====
bgneal@2 147
bgneal@2 148 - Local operations are **fast**
bgneal@2 149 - No, really, **you will** notice a big difference
bgneal@2 150 - Initial pull down of an entire repository *might* be slower than a CVCS
bgneal@2 151
bgneal@2 152 - Then again, you might be surprised
bgneal@2 153 - Mercurial, for example, stores an entire repository in less space than
bgneal@2 154 a SVN working copy in many cases
bgneal@2 155
bgneal@2 156 ----
bgneal@2 157
bgneal@2 158 Scalability
bgneal@2 159 ===========
bgneal@2 160
bgneal@2 161 - Some CVCS systems require heavy weight hardware to support the server
bgneal@2 162
bgneal@2 163 - E.g. ClearCase with a thousand users
bgneal@2 164 - With a DVCS, only pushes & pulls contact a central server
bgneal@2 165 - Most of the work is done locally
bgneal@2 166
bgneal@2 167 ----
bgneal@2 168
bgneal@2 169 Split Geography
bgneal@2 170 ===============
bgneal@2 171
bgneal@6 172 - Imagine a team split between Cedar Rapids & Richardson...
bgneal@2 173 - With a CVS, you have to pick where to put the server
bgneal@2 174 - The remote location is stuck with network latency & associated problems
bgneal@2 175 - With a DVCS, each site can have a central repository
bgneal@2 176
bgneal@2 177 - The two central repos can be synched when convenient or even scripted
bgneal@2 178
bgneal@2 179 ----
bgneal@2 180
bgneal@2 181 Flexible Workflows
bgneal@2 182 ==================
bgneal@2 183
bgneal@2 184 - There is no internal concept of a central repository
bgneal@2 185 - A central repository exits only by convention
bgneal@2 186 - More elaborate topologies and workflows can be created:
bgneal@2 187
bgneal@2 188 - A SW team may push to a central SW repo
bgneal@2 189 - Periodically changes from the SW repo are pushed to a QA repo
bgneal@2 190 - Changes from the QA repo can be pushed into a release repo
bgneal@2 191
bgneal@2 192 ----
bgneal@2 193
bgneal@2 194 Distributed Backups
bgneal@2 195 ===================
bgneal@2 196
bgneal@2 197 - With a DVCS, multiple copies of the repository exist on multiple machines
bgneal@2 198 - **Of course, this is no substitute for a real backup strategy!**
bgneal@2 199 - But usually, and with short notice, you can easily designate a repository as
bgneal@2 200 the central repository in an emergency
bgneal@2 201
bgneal@2 202 ----
bgneal@2 203
bgneal@2 204 Easier Merging
bgneal@2 205 ==============
bgneal@2 206
bgneal@2 207 - Subversion has a bad reputation for merging
bgneal@2 208
bgneal@2 209 - Some of this is not warranted...
bgneal@2 210
bgneal@2 211 - Merge tracking was added in SVN v1.5
bgneal@2 212
bgneal@2 213 - SVN does not handle file renames and tree conflicts very well
bgneal@2 214 - A lot of teams simply avoid merging out of fear
bgneal@2 215
bgneal@2 216 ----
bgneal@2 217
bgneal@2 218 Easier Merging (cont.)
bgneal@2 219 ======================
bgneal@2 220
bgneal@2 221 - Why is merging better in a DVCS?
bgneal@2 222
bgneal@2 223 - Merging simply has to work correctly and be easy in a DVCS
bgneal@2 224
bgneal@2 225 - More attention was paid to this aspect by DVCS's
bgneal@2 226
bgneal@2 227 - DVCS's use directed acyclic graphs internally to represent change sets
bgneal@2 228
bgneal@2 229 - More information is available to make merge decisions
bgneal@2 230 - Easier to find common ancestors of code
bgneal@2 231
bgneal@2 232 - Developer changes and merge changes are separate
bgneal@2 233
bgneal@2 234 - "Commit before merge"
bgneal@2 235
bgneal@2 236 ----
bgneal@2 237
bgneal@2 238 Commit Before Merge
bgneal@2 239 ===================
bgneal@2 240
bgneal@2 241 - With a CVCS:
bgneal@2 242
bgneal@2 243 - You make changes in your working copy
bgneal@2 244 - Before you can commit, you often must peform an update
bgneal@2 245
bgneal@2 246 - This may trigger a merge
bgneal@2 247 - Your changes are now mixed up with your friendly coworkers' changes
bgneal@2 248 - Sometimes this can be a problem...
bgneal@2 249
bgneal@2 250 - With a DVCS:
bgneal@2 251
bgneal@2 252 - You make changes in your working copy
bgneal@3 253 - You commit locally!
bgneal@2 254 - You can then choose to pull changes from others and merge
bgneal@2 255
bgneal@2 256 - **Your changes are already safely tucked away and can be retrieved later if things go wrong**
bgneal@2 257
bgneal@2 258 ----
bgneal@2 259
bgneal@2 260 Okay, what's the catch?
bgneal@2 261 =======================
bgneal@2 262
bgneal@2 263 Potential drawbacks to a DVCS
bgneal@2 264 -----------------------------
bgneal@2 265
bgneal@2 266 - Practically no support for locks
bgneal@2 267
bgneal@2 268 - This makes working with binary files difficult in a team environment
bgneal@2 269
bgneal@2 270 - Huge repositories are not practical
bgneal@2 271
bgneal@2 272 - Hetrogenous repositories are not practical
bgneal@2 273
bgneal@2 274 - Not a good idea to mix, say, software, systems, and firmware in the same repo
bgneal@2 275 - Not a good idea to mix multiple products in the same repo
bgneal@2 276 - Arguably, this applies to a CVCS as well
bgneal@2 277
bgneal@7 278 - No support for path-based access control
bgneal@7 279
bgneal@7 280 - With current tools, you either can access the full repo, or nothing
bgneal@7 281
bgneal@2 282 ----
bgneal@2 283
bgneal@2 284 Introduction to Mercurial
bgneal@2 285 =========================
bgneal@2 286
bgneal@5 287 - Overview
bgneal@6 288 - Repositories & working directories
bgneal@2 289 - Changesets
bgneal@4 290 - Branches & Tags
bgneal@4 291 - Example workflow
bgneal@3 292 - Command overview
bgneal@2 293
bgneal@2 294 ----
bgneal@2 295
bgneal@5 296 Mercurial Overview
bgneal@5 297 ==================
bgneal@5 298
bgneal@5 299 - Distributed Version Control System
bgneal@5 300 - Free, open source software licensed under GPL Version 2
bgneal@5 301 - Available for Microsoft Windows, GNU/Linux, Mac OS X, Solaris 11 Express
bgneal@5 302 - Written in Python with a small amount of C
bgneal@5 303 - Extensible with official and 3rd party extensions
bgneal@5 304 - TortoiseHg is a popular GUI for Windows
bgneal@5 305 - Reputation for being fast & easy to get started with
bgneal@5 306 - Can be served via Apache Web server
bgneal@5 307 - Repository hooks
bgneal@5 308 - Integrates with Trac
bgneal@5 309 - Can import history from other tools, including Subversion
bgneal@5 310
bgneal@5 311 ----
bgneal@5 312
bgneal@6 313 Repositories & Working Directories
bgneal@6 314 ==================================
bgneal@3 315
bgneal@3 316 A repository consists of two things:
bgneal@3 317
bgneal@4 318 - Your working directory (similar to a working copy in SVN)
bgneal@3 319 - The repository itself (also known as "the store")
bgneal@3 320
bgneal@3 321 - A .hg directory at the top of your working copy
bgneal@3 322
bgneal@3 323 Example::
bgneal@3 324
bgneal@4 325 $ ls -A
bgneal@3 326 .hg .hgignore images/ slides.cfg slides.css slides.html slides.rst
bgneal@3 327
bgneal@6 328 - Repositories communicate via the *push* and *pull* commands
bgneal@6 329
bgneal@6 330 - Push & Pull do not affect your working directory
bgneal@6 331
bgneal@6 332 - An *update* or *merge* must be performed to receive remote changes into your working directory
bgneal@6 333
bgneal@3 334 ----
bgneal@3 335
bgneal@3 336 What's in a Repository?
bgneal@3 337 =======================
bgneal@3 338
bgneal@3 339 A repository consists of a directed, acyclic graph of *changesets*
bgneal@3 340
bgneal@3 341 .. image:: images/repos.png
bgneal@3 342
bgneal@4 343 - Each changeset can have 0, 1, or 2 parents (and infinite children)
bgneal@3 344 - A changeset with 0 parents is the root
bgneal@3 345 - A changeset with 2 parents is the result of a merge
bgneal@4 346 - The newest changeset is called the *tip*, a special tag name
bgneal@4 347
bgneal@4 348 ----
bgneal@4 349
bgneal@4 350 What's a Changeset?
bgneal@4 351 ===================
bgneal@4 352
bgneal@4 353 A changeset is an atomic collection of changes and some meta information.
bgneal@4 354 The meta information includes:
bgneal@4 355
bgneal@4 356 - Who made the changes
bgneal@4 357 - When the changes were made
bgneal@4 358 - Why - the commit message
bgneal@4 359 - The name of the branch the changes were made on ("default" is the default)
bgneal@4 360 - A local revision number
bgneal@4 361 - A changeset ID; a 40 digit hex number (SHA-1 hash of the changeset & parents)
bgneal@4 362
bgneal@4 363 A changeset can be named by:
bgneal@4 364
bgneal@4 365 - Revision number (within a repository)
bgneal@4 366 - Changeset ID (globally)
bgneal@4 367 - Tag name
bgneal@4 368
bgneal@4 369 ----
bgneal@4 370
bgneal@4 371 Branches & Tags
bgneal@4 372 ===============
bgneal@4 373
bgneal@4 374 - In the simple case, each changeset appear in a line
bgneal@4 375 - When a changeset develops 2 or more children, a branch occurs
bgneal@4 376
bgneal@4 377 - The latest revision of a branch is called a *head*
bgneal@4 378 - A *merge* is when two branches join back together
bgneal@4 379 - Branches can be given names; the default branch name is *"default"*
bgneal@4 380
bgneal@4 381 - Changesets can be given human readable names, or *tags*
bgneal@4 382
bgneal@4 383 - *Local tags* are only visible within a repository
bgneal@4 384 - *Regular tags* are revision controlled and propagate to other repos
bgneal@4 385 - The newest head in a repository is a tag called *tip*
bgneal@4 386
bgneal@4 387 ----
bgneal@4 388
bgneal@4 389 Example Workflow
bgneal@4 390 ================
bgneal@4 391
bgneal@4 392 .. image:: images/workflow1.png
bgneal@4 393
bgneal@4 394 ----
bgneal@4 395
bgneal@4 396 Example Workflow (cont.)
bgneal@4 397 ========================
bgneal@4 398
bgneal@4 399 .. image:: images/workflow2.png
bgneal@4 400
bgneal@4 401 ----
bgneal@4 402
bgneal@4 403 Example Workflow (cont.)
bgneal@4 404 ========================
bgneal@4 405
bgneal@4 406 .. image:: images/workflow3.png
bgneal@3 407
bgneal@6 408 - Notice that after Alice's pull:
bgneal@6 409
bgneal@6 410 - Her working directory is unaffected
bgneal@6 411 - Her repository only has one head => no merging required
bgneal@6 412
bgneal@6 413
bgneal@3 414 ----
bgneal@3 415
bgneal@3 416 SVN Commands for Review
bgneal@3 417 =======================
bgneal@1 418
bgneal@1 419 Basic SVN commands:
bgneal@1 420
bgneal@1 421 - add, remove, copy, move, mkdir
bgneal@1 422 - checkout, commit, update, revert
bgneal@1 423 - merge, resolved, diff
bgneal@4 424 - status, log
bgneal@1 425 - lock, unlock
bgneal@1 426
bgneal@1 427 ----
bgneal@1 428
bgneal@4 429 Basic Mercurial Commands
bgneal@4 430 ========================
bgneal@1 431
bgneal@1 432 Mercurial (hg) vs SVN commands:
bgneal@1 433
bgneal@1 434 - add, remove, copy, move, :strike:`mkdir`
bgneal@1 435 - :strike:`checkout`, commit, update, revert
bgneal@4 436 - merge, resolve, diff, **heads**
bgneal@4 437 - status, log
bgneal@1 438 - :strike:`lock, unlock`
bgneal@1 439
bgneal@1 440 Additional "distributed commands":
bgneal@1 441
bgneal@5 442 - **clone**, **push**, **pull**
bgneal@5 443 - **incoming**, **outgoing**
bgneal@1 444
bgneal@4 445 **Not a whole lot to learn above SVN**
bgneal@4 446
bgneal@4 447 ----
bgneal@4 448
bgneal@4 449 References
bgneal@4 450 ==========
bgneal@4 451
bgneal@4 452 - Mercurial http://mercurial.selenic.com/
bgneal@4 453 - Mercurial Wiki http://mercurial.selenic.com/wiki/
bgneal@4 454 - Mercurial Book (free!) http://hgbook.red-bean.com/
bgneal@4 455 - Hg Init: A Mercurial Tutorial http://hginit.com
bgneal@4 456 - Version Control By Example (free!) http://www.ericsink.com/vcbe/
bgneal@4 457
bgneal@5 458 This presentation is available at::
bgneal@5 459
bgneal@5 460 $ hg clone https://bitbucket.org/bgneal/dvcs_intro_brownbag
bgneal@5 461
bgneal@4 462 ----
bgneal@4 463
bgneal@4 464 Questions?
bgneal@4 465 ==========
bgneal@4 466