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Basic presentation finished.
author Brian Neal <bgneal@gmail.com>
date Sat, 12 Nov 2011 14:49:09 -0600
parents 0130da731f83
children b9801a668bff
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@1 23 Perhaps you've recognized 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@2 100 It is possible for all peers to exchange changes.
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@2 172 - 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@2 278 ----
bgneal@2 279
bgneal@2 280 Introduction to Mercurial
bgneal@2 281 =========================
bgneal@2 282
bgneal@2 283 - Repositories & working copies
bgneal@2 284 - Changesets
bgneal@4 285 - Branches & Tags
bgneal@4 286 - Example workflow
bgneal@3 287 - Command overview
bgneal@2 288
bgneal@2 289 ----
bgneal@2 290
bgneal@3 291 Repositories & Working Copies
bgneal@3 292 =============================
bgneal@3 293
bgneal@3 294 A repository consists of two things:
bgneal@3 295
bgneal@4 296 - Your working directory (similar to a working copy in SVN)
bgneal@3 297 - The repository itself (also known as "the store")
bgneal@3 298
bgneal@3 299 - A .hg directory at the top of your working copy
bgneal@3 300
bgneal@3 301 Example::
bgneal@3 302
bgneal@4 303 $ ls -A
bgneal@3 304 .hg .hgignore images/ slides.cfg slides.css slides.html slides.rst
bgneal@3 305
bgneal@3 306 ----
bgneal@3 307
bgneal@3 308 What's in a Repository?
bgneal@3 309 =======================
bgneal@3 310
bgneal@3 311 A repository consists of a directed, acyclic graph of *changesets*
bgneal@3 312
bgneal@3 313 .. image:: images/repos.png
bgneal@3 314
bgneal@4 315 - Each changeset can have 0, 1, or 2 parents (and infinite children)
bgneal@3 316 - A changeset with 0 parents is the root
bgneal@3 317 - A changeset with 2 parents is the result of a merge
bgneal@4 318 - The newest changeset is called the *tip*, a special tag name
bgneal@4 319
bgneal@4 320 ----
bgneal@4 321
bgneal@4 322 What's a Changeset?
bgneal@4 323 ===================
bgneal@4 324
bgneal@4 325 A changeset is an atomic collection of changes and some meta information.
bgneal@4 326 The meta information includes:
bgneal@4 327
bgneal@4 328 - Who made the changes
bgneal@4 329 - When the changes were made
bgneal@4 330 - Why - the commit message
bgneal@4 331 - The name of the branch the changes were made on ("default" is the default)
bgneal@4 332 - A local revision number
bgneal@4 333 - A changeset ID; a 40 digit hex number (SHA-1 hash of the changeset & parents)
bgneal@4 334
bgneal@4 335 A changeset can be named by:
bgneal@4 336
bgneal@4 337 - Revision number (within a repository)
bgneal@4 338 - Changeset ID (globally)
bgneal@4 339 - Tag name
bgneal@4 340
bgneal@4 341 ----
bgneal@4 342
bgneal@4 343 Branches & Tags
bgneal@4 344 ===============
bgneal@4 345
bgneal@4 346 - In the simple case, each changeset appear in a line
bgneal@4 347 - When a changeset develops 2 or more children, a branch occurs
bgneal@4 348
bgneal@4 349 - The latest revision of a branch is called a *head*
bgneal@4 350 - A *merge* is when two branches join back together
bgneal@4 351 - Branches can be given names; the default branch name is *"default"*
bgneal@4 352
bgneal@4 353 - Changesets can be given human readable names, or *tags*
bgneal@4 354
bgneal@4 355 - *Local tags* are only visible within a repository
bgneal@4 356 - *Regular tags* are revision controlled and propagate to other repos
bgneal@4 357 - The newest head in a repository is a tag called *tip*
bgneal@4 358
bgneal@4 359 ----
bgneal@4 360
bgneal@4 361 Example Workflow
bgneal@4 362 ================
bgneal@4 363
bgneal@4 364 .. image:: images/workflow1.png
bgneal@4 365
bgneal@4 366 ----
bgneal@4 367
bgneal@4 368 Example Workflow (cont.)
bgneal@4 369 ========================
bgneal@4 370
bgneal@4 371 .. image:: images/workflow2.png
bgneal@4 372
bgneal@4 373 ----
bgneal@4 374
bgneal@4 375 Example Workflow (cont.)
bgneal@4 376 ========================
bgneal@4 377
bgneal@4 378 .. image:: images/workflow3.png
bgneal@3 379
bgneal@3 380 ----
bgneal@3 381
bgneal@3 382 SVN Commands for Review
bgneal@3 383 =======================
bgneal@1 384
bgneal@1 385 Basic SVN commands:
bgneal@1 386
bgneal@1 387 - add, remove, copy, move, mkdir
bgneal@1 388 - checkout, commit, update, revert
bgneal@1 389 - merge, resolved, diff
bgneal@4 390 - status, log
bgneal@1 391 - lock, unlock
bgneal@1 392
bgneal@1 393 ----
bgneal@1 394
bgneal@4 395 Basic Mercurial Commands
bgneal@4 396 ========================
bgneal@1 397
bgneal@1 398 Mercurial (hg) vs SVN commands:
bgneal@1 399
bgneal@1 400 - add, remove, copy, move, :strike:`mkdir`
bgneal@1 401 - :strike:`checkout`, commit, update, revert
bgneal@4 402 - merge, resolve, diff, **heads**
bgneal@4 403 - status, log
bgneal@1 404 - :strike:`lock, unlock`
bgneal@1 405
bgneal@1 406 Additional "distributed commands":
bgneal@1 407
bgneal@1 408 - clone, push, pull
bgneal@1 409 - incoming, outgoing
bgneal@1 410 - serve
bgneal@1 411
bgneal@4 412 **Not a whole lot to learn above SVN**
bgneal@4 413
bgneal@4 414 ----
bgneal@4 415
bgneal@4 416 References
bgneal@4 417 ==========
bgneal@4 418
bgneal@4 419 - Mercurial http://mercurial.selenic.com/
bgneal@4 420 - Mercurial Wiki http://mercurial.selenic.com/wiki/
bgneal@4 421 - Mercurial Book (free!) http://hgbook.red-bean.com/
bgneal@4 422 - Hg Init: A Mercurial Tutorial http://hginit.com
bgneal@4 423 - Version Control By Example (free!) http://www.ericsink.com/vcbe/
bgneal@4 424
bgneal@4 425 ----
bgneal@4 426
bgneal@4 427 Questions?
bgneal@4 428 ==========
bgneal@4 429