bgneal@1: .. role:: strike
bgneal@1:     :class: strike
bgneal@1: 
bgneal@0: Introduction to Distributed Version Control with Mercurial
bgneal@0: ==========================================================
bgneal@0: 
bgneal@0: ----
bgneal@0: 
bgneal@1: (Sublimal Message)
bgneal@1: ==================
bgneal@1: 
bgneal@4: .. image:: images/stop.jpg
bgneal@1: 
bgneal@1: ----
bgneal@1: 
bgneal@0: # whoami
bgneal@0: ========
bgneal@0: 
bgneal@0: Brian Neal <bgneal1@rockwellcollins.com>
bgneal@0: 
bgneal@0: Started at Rockwell Collins in July 1999
bgneal@0: 
bgneal@5: You might remember me from the following programs:
bgneal@0: 
bgneal@0: - UMS (July 1999 - Spring 2000)
bgneal@0: - Surgical Strike - (Spring - Fall 2000)
bgneal@0: - JTRS 2B - (Fall 2000 - Summer 2001)
bgneal@0: - SCAMP SEP - (Summer 2001 - October 2004)
bgneal@0: - TTNT (January 2005 - Present)
bgneal@0: 
bgneal@0: ----
bgneal@0: 
bgneal@0: Brief History of Version Control Tools
bgneal@0: ======================================
bgneal@0: 
bgneal@0: First Generation
bgneal@0: ----------------
bgneal@0: 
bgneal@1: - No networking!
bgneal@1: - Concurrency method: locks
bgneal@0: - Examples:
bgneal@0:   
bgneal@0:   - SCCS - 1972
bgneal@0:   - RCS - 1982 
bgneal@0: 
bgneal@0: ----
bgneal@0: 
bgneal@0: Brief History of Version Control Tools
bgneal@0: ======================================
bgneal@0: 
bgneal@0: Second Generation
bgneal@0: -----------------
bgneal@0: 
bgneal@0: - Client/Server networking; CVCS (Centralized Version Control)
bgneal@1: - Concurrency method: merge before commit
bgneal@0: - Examples:
bgneal@0:   
bgneal@0:   - CVS - 1990
bgneal@0:   - IBM Rational ClearCase - 1992
bgneal@0:   - Visual SourceSafe - 1994
bgneal@0:   - Perforce - 1995
bgneal@0:   - SVN - 2000
bgneal@0: 
bgneal@0: ----
bgneal@0: 
bgneal@0: Brief History of Version Control Tools
bgneal@0: ======================================
bgneal@0: 
bgneal@0: Third Generation
bgneal@0: ----------------
bgneal@0: 
bgneal@0: - Distributed networking; DVCS (Distributed Version Control)
bgneal@1: - Concurrency method: commit then merge
bgneal@1: - Examples:
bgneal@0: 
bgneal@0:   - Bitkeeper - 2000
bgneal@0:   - Darcs - 2003
bgneal@0:   - Monotone - 2003
bgneal@0:   - Git - 2005
bgneal@0:   - **Mercurial** - 2005
bgneal@0:   - Fossil - 2006
bgneal@0:   - Bazaar - 2007
bgneal@1:   - Veracity - 2011
bgneal@1: 
bgneal@1: ----
bgneal@1: 
bgneal@1: What is a CVCS Again?
bgneal@1: =====================
bgneal@1: 
bgneal@1: .. image:: images/cvcs.png
bgneal@1: 
bgneal@1: ----
bgneal@1: 
bgneal@2: So what's a DVCS look like?
bgneal@2: ===========================
bgneal@2: 
bgneal@2: .. image:: images/dvcs.png
bgneal@2: 
bgneal@2: All repositories are peers. By convention only, one repository is designated the master.
bgneal@6: It is possible for all peers to exchange changes (via *push* and *pull* operations).
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@2: What does a DVCS buy you?
bgneal@2: =========================
bgneal@2: 
bgneal@2: - Private workspaces
bgneal@2: - Offline mode
bgneal@2: - Speed
bgneal@2: - Scalability
bgneal@2: - Split Geography
bgneal@2: - Flexible workflows
bgneal@2: - Distributed backups
bgneal@2: - **Easier merging**
bgneal@2: - **Commit before merge**
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Private Workspaces
bgneal@2: ==================
bgneal@2: 
bgneal@2: - You can safely experiment in your local repository
bgneal@2: - Commit as often as you like without affecting the team
bgneal@10:    
bgneal@10:   - Encourages "micro-commits"
bgneal@10:   - With SVN, people often hold back until an entire feature is complete
bgneal@10: 
bgneal@2: - Encourages experimentation
bgneal@2: 
bgneal@2:   - Make cheap repository clones to try things out
bgneal@2:   - Not visible to coworkers
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Offline Mode
bgneal@2: ============
bgneal@2:   
bgneal@2: - Work when you have spotty or no network access
bgneal@2: - Full access to the repo when offline
bgneal@2: - Can work on multiple tasks offline
bgneal@2: 
bgneal@2:  - Work on bug report #1
bgneal@2:  - Commit
bgneal@2:  - Work on bug report #2
bgneal@2:  - With a CVCS, you'd have both fixes in the same pending commit
bgneal@2:  
bgneal@2: ----
bgneal@2: 
bgneal@2: Speed
bgneal@2: =====
bgneal@2: 
bgneal@2: - Local operations are **fast**
bgneal@8: 
bgneal@8:   - No, really, **you will** notice a big difference
bgneal@8:   - Switching between branches will blow your mind
bgneal@8: 
bgneal@2: - Initial pull down of an entire repository *might* be slower than a CVCS
bgneal@2: 
bgneal@2:   - Then again, you might be surprised
bgneal@2:   - Mercurial, for example, stores an entire repository in less space than
bgneal@2:     a SVN working copy in many cases
bgneal@8: 
bgneal@2:  
bgneal@2: ----
bgneal@2: 
bgneal@2: Scalability
bgneal@2: ===========
bgneal@2: 
bgneal@2: - Some CVCS systems require heavy weight hardware to support the server
bgneal@2: 
bgneal@2:   - E.g. ClearCase with a thousand users
bgneal@2:   - With a DVCS, only pushes & pulls contact a central server
bgneal@2:   - Most of the work is done locally
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Split Geography
bgneal@2: ===============
bgneal@2: 
bgneal@6: - Imagine a team split between Cedar Rapids & Richardson...
bgneal@10: - With a CVCS, you have to pick where to put the server
bgneal@2: - The remote location is stuck with network latency & associated problems
bgneal@2: - With a DVCS, each site can have a central repository
bgneal@2: 
bgneal@2:   - The two central repos can be synched when convenient or even scripted
bgneal@2:  
bgneal@9: .. image:: images/split_geography.png
bgneal@9: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Flexible Workflows
bgneal@2: ==================
bgneal@2: 
bgneal@2: - There is no internal concept of a central repository
bgneal@2: - A central repository exits only by convention
bgneal@2: - More elaborate topologies and workflows can be created:
bgneal@2: 
bgneal@2:   - A SW team may push to a central SW repo
bgneal@2:   - Periodically changes from the SW repo are pushed to a QA repo
bgneal@2:   - Changes from the QA repo can be pushed into a release repo
bgneal@9: 
bgneal@9: .. image:: images/flexible_workflows.png
bgneal@2:  
bgneal@2: ----
bgneal@2: 
bgneal@2: Distributed Backups
bgneal@2: ===================
bgneal@2: 
bgneal@2: - With a DVCS, multiple copies of the repository exist on multiple machines
bgneal@2: - **Of course, this is no substitute for a real backup strategy!**
bgneal@2: - But usually, and with short notice, you can easily designate a repository as
bgneal@2:   the central repository in an emergency
bgneal@2:  
bgneal@2: ----
bgneal@2: 
bgneal@2: Easier Merging
bgneal@2: ==============
bgneal@2: 
bgneal@2: - Subversion has a bad reputation for merging
bgneal@2: 
bgneal@2:   - Some of this is not warranted...
bgneal@2: 
bgneal@2:     - Merge tracking was added in SVN v1.5
bgneal@2: 
bgneal@2:   - SVN does not handle file renames and tree conflicts very well
bgneal@2:   - A lot of teams simply avoid merging out of fear
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Easier Merging (cont.)
bgneal@2: ======================
bgneal@2: 
bgneal@2: - Why is merging better in a DVCS?
bgneal@2: 
bgneal@2:   - Merging simply has to work correctly and be easy in a DVCS
bgneal@2: 
bgneal@2:     - More attention was paid to this aspect by DVCS's
bgneal@2: 
bgneal@2:   - DVCS's use directed acyclic graphs internally to represent change sets
bgneal@2: 
bgneal@2:     - More information is available to make merge decisions
bgneal@2:     - Easier to find common ancestors of code
bgneal@2: 
bgneal@2:   - Developer changes and merge changes are separate
bgneal@2: 
bgneal@2:     - "Commit before merge"
bgneal@2:  
bgneal@2: ----
bgneal@2: 
bgneal@2: Commit Before Merge
bgneal@2: ===================
bgneal@2: 
bgneal@2: - With a CVCS:
bgneal@2: 
bgneal@2:   - You make changes in your working copy
bgneal@2:   - Before you can commit, you often must peform an update
bgneal@2:      
bgneal@2:     - This may trigger a merge
bgneal@2:     - Your changes are now mixed up with your friendly coworkers' changes
bgneal@2:     - Sometimes this can be a problem...
bgneal@2: 
bgneal@2: - With a DVCS:
bgneal@2: 
bgneal@2:   - You make changes in your working copy
bgneal@3:   - You commit locally!
bgneal@2:   - You can then choose to pull changes from others and merge
bgneal@2: 
bgneal@2:     - **Your changes are already safely tucked away and can be retrieved later if things go wrong**
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Okay, what's the catch?
bgneal@2: =======================
bgneal@2: 
bgneal@2: Potential drawbacks to a DVCS
bgneal@2: -----------------------------
bgneal@2: 
bgneal@2: - Practically no support for locks
bgneal@2: 
bgneal@2:   - This makes working with binary files difficult in a team environment
bgneal@2: 
bgneal@2: - Huge repositories are not practical
bgneal@2: 
bgneal@2: - Hetrogenous repositories are not practical
bgneal@2: 
bgneal@2:   - Not a good idea to mix, say, software, systems, and firmware in the same repo
bgneal@2:   - Not a good idea to mix multiple products in the same repo
bgneal@2:   - Arguably, this applies to a CVCS as well
bgneal@2: 
bgneal@7: - No support for path-based access control
bgneal@7: 
bgneal@7:   - With current tools, you either can access the full repo, or nothing
bgneal@7: 
bgneal@2: ----
bgneal@2: 
bgneal@2: Introduction to Mercurial
bgneal@2: =========================
bgneal@2: 
bgneal@5: - Overview
bgneal@6: - Repositories & working directories
bgneal@2: - Changesets
bgneal@4: - Branches & Tags
bgneal@4: - Example workflow
bgneal@3: - Command overview
bgneal@2: 
bgneal@2: ----
bgneal@2: 
bgneal@5: Mercurial Overview
bgneal@5: ==================
bgneal@5: 
bgneal@5: - Distributed Version Control System
bgneal@5: - Free, open source software licensed under GPL Version 2
bgneal@5: - Available for Microsoft Windows, GNU/Linux, Mac OS X, Solaris 11 Express
bgneal@5: - Written in Python with a small amount of C
bgneal@5: - Extensible with official and 3rd party extensions
bgneal@5: - TortoiseHg is a popular GUI for Windows
bgneal@5: - Reputation for being fast & easy to get started with
bgneal@5: - Can be served via Apache Web server
bgneal@5: - Repository hooks
bgneal@5: - Integrates with Trac
bgneal@5: - Can import history from other tools, including Subversion
bgneal@5: 
bgneal@5: ----
bgneal@5: 
bgneal@6: Repositories & Working Directories
bgneal@6: ==================================
bgneal@3: 
bgneal@3: A repository consists of two things:
bgneal@3: 
bgneal@4: - Your working directory (similar to a working copy in SVN)
bgneal@3: - The repository itself (also known as "the store")
bgneal@3: 
bgneal@3:   - A .hg directory at the top of your working copy
bgneal@3: 
bgneal@3: Example::
bgneal@3: 
bgneal@4:    $ ls -A
bgneal@3:    .hg  .hgignore  images/  slides.cfg  slides.css  slides.html  slides.rst
bgneal@3: 
bgneal@6: - Repositories communicate via the *push* and *pull* commands
bgneal@6: 
bgneal@6:   - Push & Pull do not affect your working directory
bgneal@6:   
bgneal@6:     - An *update* or *merge* must be performed to receive remote changes into your working directory
bgneal@6: 
bgneal@3: ----
bgneal@3: 
bgneal@3: What's in a Repository?
bgneal@3: =======================
bgneal@3: 
bgneal@3: A repository consists of a directed, acyclic graph of *changesets*
bgneal@3: 
bgneal@3: .. image:: images/repos.png
bgneal@3: 
bgneal@4: - Each changeset can have 0, 1, or 2 parents (and infinite children)
bgneal@3: - A changeset with 0 parents is the root
bgneal@3: - A changeset with 2 parents is the result of a merge
bgneal@4: - The newest changeset is called the *tip*, a special tag name
bgneal@4: 
bgneal@4: ----
bgneal@4: 
bgneal@4: What's a Changeset?
bgneal@4: ===================
bgneal@4: 
bgneal@4: A changeset is an atomic collection of changes and some meta information. 
bgneal@4: The meta information includes:
bgneal@4: 
bgneal@4: - Who made the changes
bgneal@4: - When the changes were made
bgneal@4: - Why - the commit message
bgneal@4: - The name of the branch the changes were made on ("default" is the default)
bgneal@4: - A local revision number
bgneal@4: - A changeset ID; a 40 digit hex number (SHA-1 hash of the changeset & parents)
bgneal@4: 
bgneal@4: A changeset can be named by:
bgneal@4: 
bgneal@4: - Revision number (within a repository)
bgneal@4: - Changeset ID (globally)
bgneal@4: - Tag name
bgneal@4: 
bgneal@4: ----
bgneal@4: 
bgneal@4: Branches & Tags
bgneal@4: ===============
bgneal@4: 
bgneal@4: - In the simple case, each changeset appear in a line
bgneal@4: - When a changeset develops 2 or more children, a branch occurs
bgneal@4: 
bgneal@4:   - The latest revision of a branch is called a *head*
bgneal@4:   - A *merge* is when two branches join back together
bgneal@4:   - Branches can be given names; the default branch name is *"default"*
bgneal@4: 
bgneal@4: - Changesets can be given human readable names, or *tags*
bgneal@4: 
bgneal@4:   - *Local tags* are only visible within a repository
bgneal@4:   - *Regular tags* are revision controlled and propagate to other repos 
bgneal@4:   - The newest head in a repository is a tag called *tip*
bgneal@4: 
bgneal@4: ----
bgneal@4: 
bgneal@4: Example Workflow
bgneal@4: ================
bgneal@4: 
bgneal@4: .. image:: images/workflow1.png
bgneal@4: 
bgneal@4: ----
bgneal@4: 
bgneal@4: Example Workflow (cont.)
bgneal@4: ========================
bgneal@4: 
bgneal@4: .. image:: images/workflow2.png
bgneal@4: 
bgneal@4: ----
bgneal@4: 
bgneal@4: Example Workflow (cont.)
bgneal@4: ========================
bgneal@4: 
bgneal@4: .. image:: images/workflow3.png
bgneal@3: 
bgneal@6: - Notice that after Alice's pull:
bgneal@6:   
bgneal@6:   - Her working directory is unaffected
bgneal@6:   - Her repository only has one head => no merging required
bgneal@6:   
bgneal@6: 
bgneal@3: ----
bgneal@3: 
bgneal@3: SVN Commands for Review
bgneal@3: =======================
bgneal@1: 
bgneal@1: Basic SVN commands:
bgneal@1: 
bgneal@1: - add, remove, copy, move, mkdir
bgneal@1: - checkout, commit, update, revert
bgneal@1: - merge, resolved, diff
bgneal@4: - status, log
bgneal@1: - lock, unlock
bgneal@1: 
bgneal@1: ----
bgneal@1: 
bgneal@4: Basic Mercurial Commands
bgneal@4: ========================
bgneal@1: 
bgneal@1: Mercurial (hg) vs SVN commands:
bgneal@1: 
bgneal@1: - add, remove, copy, move, :strike:`mkdir`
bgneal@1: - :strike:`checkout`, commit, update, revert
bgneal@4: - merge, resolve, diff, **heads**
bgneal@4: - status, log
bgneal@1: - :strike:`lock, unlock`
bgneal@1: 
bgneal@1: Additional "distributed commands":
bgneal@1: 
bgneal@5: - **clone**, **push**, **pull**
bgneal@5: - **incoming**, **outgoing**
bgneal@1: 
bgneal@4: **Not a whole lot to learn above SVN**
bgneal@4: 
bgneal@4: ----
bgneal@4: 
bgneal@4: References
bgneal@4: ==========
bgneal@4: 
bgneal@4: - Mercurial http://mercurial.selenic.com/
bgneal@4: - Mercurial Wiki http://mercurial.selenic.com/wiki/
bgneal@4: - Mercurial Book (free!) http://hgbook.red-bean.com/
bgneal@4: - Hg Init: A Mercurial Tutorial http://hginit.com
bgneal@4: - Version Control By Example (free!) http://www.ericsink.com/vcbe/
bgneal@4: 
bgneal@5: This presentation is available at::
bgneal@5: 
bgneal@5:    $ hg clone https://bitbucket.org/bgneal/dvcs_intro_brownbag
bgneal@5: 
bgneal@4: ----
bgneal@4: 
bgneal@4: Questions?
bgneal@4: ==========
bgneal@4: