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| Mercurial's decentralized development model can be confusing to new users. This page attempts to illustrate some of the basic concepts. See the ["Tutorial"] for step-by-step instructions. [[TableOfContents]] == What's in a Repository == Mercurial [:Repository:repositories] contain a [:WorkingDirectory:working directory] coupled with a store: {{{#!dot digraph G { compound=true; rankdir = LR background="#999999"; subgraph cluster_1 { style=filled; color="#eeeeee"; node [shape=box,style=filled,color=lightgray]; "rev 0" -> "rev 1" -> "rev 2" -> "rev 3"; label = "store"; } subgraph cluster_0 { style=filled; color=lightgrey; node [style=filled,color=white]; edge [style=invis]; "main.c"-> "main.h" -> ".hgignore" -> ".hgtags" label="working directory"; } "rev 2" -> ".hgtags" [lhead = cluster_0 constraint=false] } }}} The store contains the '''complete''' history of the project. Unlike traditional [:SCM:SCMs], where there's only one central copy of this history, every working directory is paired with a private copy of the history. This allows development to go on in parallel. The working directory contains a copy of the project's files at a given point in time (eg rev 2), ready for editing. Because [:Tag:tags] and ignored files are revision-controlled, they are also included. == Committing Changes == When you [:Commit:commit], the state of the working directory relative to its [:Parent:parents] is recorded as a new [:Revision:revision]: {{{#!dot digraph G { compound=true; rankdir = LR background="#999999"; subgraph cluster_1 { style=filled; color="#eeeeee"; node [shape=box,style=filled,color=lightgray]; "rev 0" -> "rev 1" -> "rev 2" -> "rev 3"; "rev 2" -> "rev 4"; label = "store"; } subgraph cluster_0 { style=filled; color=lightgrey; node [style=filled,color=white]; edge [style=invis]; "main.c"-> "main.h" -> ".hgignore" -> ".hgtags" label="working directory"; } "rev 2" -> ".hgtags" [style = dotted lhead = cluster_0 constraint=false] "rev 4" -> ".hgtags" [lhead = cluster_0 constraint=false] ".hgtags" -> "rev 4" [color = red label = "commit" ltail = cluster_0 constraint=false] } }}} Note here that revision 4 is a '''branch''' of revision 2, which was the revision in the working directory. Now revision 4 is the working directory's '''parent'''. == Revisions, Changesets, Heads, and Tip == Mercurial groups related changes to multiple files into single atomic [:ChangeSet:changesets], which are revisions of the whole project. These each get a sequential [:RevisionNumber:revision number]. Because Mercurial allows distributed parallel development, these revision numbers may disagree between users. So Mercurial also assigns each revision a global [:ChangeSetID:changeset ID]. Changeset IDs are 40-digit hexadecimal numbers, but they can be abbreviated to any unambiguous prefix, like "e38487". {{{#!dot digraph { rankdir = LR node [shape=box] "rev 0:838e" -> "rev 1:34ef" -> "rev 2:4563" "rev 1:34ef" -> "rev 3:fe56" "rev 2:4563" -> "rev 4:ac98" "rev 3:fe56" -> "rev 4:ac98" "rev 4:ac98" -> "rev 5:0345" "rev 4:ac98" -> "rev 6:19e3 (tip)" label="example history" } }}} Branches and [:Merge:merges] in the revision history can occur at any point. Each unmerged branch creates a new [:Head:head] of the revision history. Here, revisions 5 and 6 are heads. Mercurial considers revision 6 to be the [:Tip:tip] of the repository, the head with the highest revision number. == Cloning, Making Changes, Merging, and Pulling == Let's start with a user Alice, who has a store that looks like: {{{#!dot digraph { label="Alice's Repo" rankdir = LR node [shape=box] a->b->c->d } }}} Bob [:Clone:clones] this repo, and ends up with a complete copy of Alice's store (though his working directory is independent!): {{{#!dot digraph { label="Bob's Repo" rankdir = LR node [shape=box] a->b->c->d } }}} Bob then [:Commit:commits] a couple changes: {{{#!dot digraph { label="Bob's Repo" rankdir = LR node [shape=box] a->b->c->d->e->f e [color=blue] f [color=blue] } }}} Alice then makes her own change in parallel: {{{#!dot digraph { label="Alice's Repo" rankdir = LR node [shape=box] a->b->c->d->g g [color=red] } }}} Bob then [:Pull:pulls] Alice's repo to synchronize. This copies all of Alice's changes into Bob's repo: {{{#!dot digraph { label="Bob's Repo" rankdir = LR node [shape=box] a->b->c->d->e->f e [color=blue] f [color=blue] d->g g [color=red;label="g (tip)"] } }}} Because Alice's '''g''' is the newest head in Bob's repository, it's now the '''tip'''. Bob then does a [:Merge:merge] which combines the last change he was working on ('''f''') with the tip, commits the result, and ends up with: {{{#!dot digraph { label="Bob's Repo" rankdir = LR node [shape=box] a->b->c->d->e->f e [color=blue] f [color=blue] d->g g [color=red] f->h g->h h [color=green;label="h (tip)"] } }}} Now if Alice '''pulls''' from Bob, she will get Bob's changes e, f, and h, and they will be fully synchronized: {{{#!dot digraph { label="Alice's Repo" rankdir = LR node [shape=box] a->b->c->d->g d->e->f e [color=blue] f [color=blue] g [color=red] f->h g->h h [color=green;label="h (tip)"] } }}} == A Decentralized System == Mercurial is a completely decentralized system, and thus has no internal notion of a central repository. Thus users are free to define their own topologies for sharing changes (see CommunicatingChanges): {{{#!dot digraph { Alice -> Central Central -> Alice Bob -> Central Alice -> Bob Alice -> Carl Carl -> Central Bob -> Carl Carl -> Bob "Carl's Laptop" -> Carl Carl -> "Carl's Laptop" "Carl's Laptop" -> Central Central [style=fill;color=blue;label="Main Public Repo"] label="A Mercurial Network" } }}} For a hands-on introduction to using Mercurial, see the ["Tutorial"]. |
The writer is called Nickolas Courtright but people always misspell it. One of his favorite hobbies is baseball but he can't make it his profession. North Dakota is the only place he's been residing in and he loves every day living there. Supervising is his day job now. He's been working on his website for some time now. Check it out here: http://www.youtube.com/watch?v=Fo3gdIFkUCM |
The writer is called Nickolas Courtright but people always misspell it. One of his favorite hobbies is baseball but he can't make it his profession. North Dakota is the only place he's been residing in and he loves every day living there. Supervising is his day job now. He's been working on his website for some time now. Check it out here: http://www.youtube.com/watch?v=Fo3gdIFkUCM