Show More
@@ -1,214 +1,215 b'' | |||||
1 | Mercurial Frequently Asked Questions |
|
1 | Mercurial Frequently Asked Questions | |
|
2 | ==================================== | |||
2 |
|
3 | |||
3 | Section 1: General Usage |
|
4 | Section 1: General Usage | |
4 | ------------------------ |
|
5 | ------------------------ | |
5 |
|
6 | |||
6 |
Q. I did an |
|
7 | .Q. I did an "hg pull" and my working directory is empty! | |
7 |
|
8 | |||
8 | There are two parts to Mercurial: the repository and the working |
|
9 | There are two parts to Mercurial: the repository and the working | |
9 |
directory. |
|
10 | directory. "hg pull" pulls all new changes from a remote repository | |
10 | into the local one but doesn't alter the working directory. |
|
11 | into the local one but doesn't alter the working directory. | |
11 |
|
12 | |||
12 | This keeps you from upsetting your work in progress, which may not be |
|
13 | This keeps you from upsetting your work in progress, which may not be | |
13 | ready to merge with the new changes you've pulled and also allows you |
|
14 | ready to merge with the new changes you've pulled and also allows you | |
14 | to manage merging more easily (see below about best practices). |
|
15 | to manage merging more easily (see below about best practices). | |
15 |
|
16 | |||
16 |
To update your working directory, run |
|
17 | To update your working directory, run "hg update". If you're sure you | |
17 |
want to update your working directory on a pull, you can also use |
|
18 | want to update your working directory on a pull, you can also use "hg | |
18 |
pull -u |
|
19 | pull -u". This will refuse to merge or overwrite local changes. | |
19 |
|
20 | |||
20 |
|
21 | |||
21 |
Q. What |
|
22 | .Q. What are revision numbers, changeset IDs, and tags? | |
22 | and tags? |
|
|||
23 |
|
23 | |||
24 | Mercurial will generally allow you to refer to a revision in three |
|
24 | Mercurial will generally allow you to refer to a revision in three | |
25 | ways: by revision number, by changeset ID, and by tag. |
|
25 | ways: by revision number, by changeset ID, and by tag. | |
26 |
|
26 | |||
27 | A revision number is a simple decimal number that corresponds with the |
|
27 | A revision number is a simple decimal number that corresponds with the | |
28 | ordering of commits in the local repository. It is important to |
|
28 | ordering of commits in the local repository. It is important to | |
29 | understand that this ordering can change from machine to machine due |
|
29 | understand that this ordering can change from machine to machine due | |
30 | to Mercurial's distributed, decentralized architecture. |
|
30 | to Mercurial's distributed, decentralized architecture. | |
31 |
|
31 | |||
32 | This is where changeset IDs come in. A changeset ID is a 160-bit |
|
32 | This is where changeset IDs come in. A changeset ID is a 160-bit | |
33 | identifier that uniquely describes a changeset and its position in the |
|
33 | identifier that uniquely describes a changeset and its position in the | |
34 | change history, regardless of which machine it's on. This is |
|
34 | change history, regardless of which machine it's on. This is | |
35 | represented to the user as a 40 digit hexadecimal number. As that |
|
35 | represented to the user as a 40 digit hexadecimal number. As that | |
36 | tends to be unwieldy, Mercurial will accept any unambiguous substring |
|
36 | tends to be unwieldy, Mercurial will accept any unambiguous substring | |
37 | of that number when specifying versions. It will also generally print |
|
37 | of that number when specifying versions. It will also generally print | |
38 | these numbers in "short form", which is the first 12 digits. |
|
38 | these numbers in "short form", which is the first 12 digits. | |
39 |
|
39 | |||
40 | You should always use some form of changeset ID rather than the local |
|
40 | You should always use some form of changeset ID rather than the local | |
41 | revision number when discussing revisions with other Mercurial users |
|
41 | revision number when discussing revisions with other Mercurial users | |
42 | as they may have different revision numbering on their system. |
|
42 | as they may have different revision numbering on their system. | |
43 |
|
43 | |||
44 | Finally, a tag is an arbitrary string that has been assigned a |
|
44 | Finally, a tag is an arbitrary string that has been assigned a | |
45 | correspondence to a changeset ID. This lets you refer to revisions |
|
45 | correspondence to a changeset ID. This lets you refer to revisions | |
46 | symbolically. |
|
46 | symbolically. | |
47 |
|
47 | |||
48 |
|
48 | |||
49 | Q. What are branches, heads, and the tip? |
|
49 | .Q. What are branches, heads, and the tip? | |
50 |
|
50 | |||
51 | The central concept of Mercurial is branching. A 'branch' is simply |
|
51 | The central concept of Mercurial is branching. A 'branch' is simply | |
52 | an independent line of development. In most other version control |
|
52 | an independent line of development. In most other version control | |
53 | systems, all users generally commit to the same line of development |
|
53 | systems, all users generally commit to the same line of development | |
54 | called 'the trunk' or 'the main branch'. In Mercurial, every developer |
|
54 | called 'the trunk' or 'the main branch'. In Mercurial, every developer | |
55 | effectively works on a private branch and there is no internal concept |
|
55 | effectively works on a private branch and there is no internal concept | |
56 | of 'the main branch'. |
|
56 | of 'the main branch'. | |
57 |
|
57 | |||
58 | Thus Mercurial works hard to make repeated merging between branches |
|
58 | Thus Mercurial works hard to make repeated merging between branches | |
59 |
easy. Simply run |
|
59 | easy. Simply run "hg pull" and "hg update -m" and commit the result. | |
60 |
|
60 | |||
61 | 'Heads' are simply the most recent commits on a branch. Technically, |
|
61 | 'Heads' are simply the most recent commits on a branch. Technically, | |
62 | they are changesets which have no children. Merging is the process of |
|
62 | they are changesets which have no children. Merging is the process of | |
63 | joining points on two branches into one, usually at their current |
|
63 | joining points on two branches into one, usually at their current | |
64 |
heads. Use |
|
64 | heads. Use "hg heads" to find the heads in the current repository. | |
65 |
|
65 | |||
66 | The 'tip' is the most recently changed head, and also the highest |
|
66 | The 'tip' is the most recently changed head, and also the highest | |
67 | numbered revision. If you have just made a commit, that commit will be |
|
67 | numbered revision. If you have just made a commit, that commit will be | |
68 | the head. Alternately, if you have just pulled from another |
|
68 | the head. Alternately, if you have just pulled from another | |
69 | repository, the tip of that repository becomes the current tip. |
|
69 | repository, the tip of that repository becomes the current tip. | |
70 |
|
70 | |||
71 | The 'tip' is the default revision for many commands such as update, |
|
71 | The 'tip' is the default revision for many commands such as update, | |
72 | and also functions as a special symbolic tag. |
|
72 | and also functions as a special symbolic tag. | |
73 |
|
73 | |||
74 |
|
74 | |||
75 | Q. How does merging work? |
|
75 | .Q. How does merging work? | |
76 |
|
76 | |||
77 | The merge process is simple. Usually you will want to merge the tip |
|
77 | The merge process is simple. Usually you will want to merge the tip | |
78 |
into your working directory. Thus you run |
|
78 | into your working directory. Thus you run "hg update -m" and Mercurial | |
79 | will incorporate the changes from tip into your local changes. |
|
79 | will incorporate the changes from tip into your local changes. | |
80 |
|
80 | |||
81 | The first step of this process is tracing back through the history of |
|
81 | The first step of this process is tracing back through the history of | |
82 | changesets and finding the 'common ancestor' of the two versions that |
|
82 | changesets and finding the 'common ancestor' of the two versions that | |
83 | are being merged. This is done on a project-wide and a file by file |
|
83 | are being merged. This is done on a project-wide and a file by file | |
84 | basis. |
|
84 | basis. | |
85 |
|
85 | |||
86 | For files that have been changed in both projects, a three-way merge |
|
86 | For files that have been changed in both projects, a three-way merge | |
87 | is attempted to add the changes made remotely into the changes made |
|
87 | is attempted to add the changes made remotely into the changes made | |
88 | locally. If there are conflicts between these changes, the user is |
|
88 | locally. If there are conflicts between these changes, the user is | |
89 | prompted to interactively resolve them. |
|
89 | prompted to interactively resolve them. | |
90 |
|
90 | |||
91 | Mercurial uses a helper tool for this, which is usually found by the |
|
91 | Mercurial uses a helper tool for this, which is usually found by the | |
92 | hgmerge script. Example tools include tkdiff, kdiff3, and the classic |
|
92 | hgmerge script. Example tools include tkdiff, kdiff3, and the classic | |
93 | RCS merge. |
|
93 | RCS merge. | |
94 |
|
94 | |||
95 | After you've completed the merge and you're satisfied that the results |
|
95 | After you've completed the merge and you're satisfied that the results | |
96 | are correct, it's a good idea to commit your changes. Mercurial won't |
|
96 | are correct, it's a good idea to commit your changes. Mercurial won't | |
97 | allow you to perform another merge until you've done this commit as |
|
97 | allow you to perform another merge until you've done this commit as | |
98 | that would lose important history that will be needed for future |
|
98 | that would lose important history that will be needed for future | |
99 | merges. |
|
99 | merges. | |
100 |
|
100 | |||
101 |
|
101 | |||
102 | Q. How do tags work in Mercurial? |
|
102 | .Q. How do tags work in Mercurial? | |
103 |
|
103 | |||
104 | Tags work slightly differently in Mercurial than most revision |
|
104 | Tags work slightly differently in Mercurial than most revision | |
105 | systems. The design attempts to meet the following requirements: |
|
105 | systems. The design attempts to meet the following requirements: | |
106 |
|
106 | |||
107 | - be version controlled and mergeable just like any other file |
|
107 | - be version controlled and mergeable just like any other file | |
108 | - allow signing of tags |
|
108 | - allow signing of tags | |
109 | - allow adding a tag to an already committed changeset |
|
109 | - allow adding a tag to an already committed changeset | |
110 | - allow changing tags in the future |
|
110 | - allow changing tags in the future | |
111 |
|
111 | |||
112 | Thus Mercurial stores tags as a file in the working dir. This file is |
|
112 | Thus Mercurial stores tags as a file in the working dir. This file is | |
113 | called .hgtags and consists of a list of changeset IDs and their |
|
113 | called .hgtags and consists of a list of changeset IDs and their | |
114 | corresponding tags. To add a tag to the system, simply add a line to |
|
114 | corresponding tags. To add a tag to the system, simply add a line to | |
115 |
this file and then commit it for it to take effect. The |
|
115 | this file and then commit it for it to take effect. The "hg tag" | |
116 |
command will do this for you and |
|
116 | command will do this for you and "hg tags" will show the currently | |
117 | effective tags. |
|
117 | effective tags. | |
118 |
|
118 | |||
119 | Note that because tags refer to changeset IDs and the changeset ID is |
|
119 | Note that because tags refer to changeset IDs and the changeset ID is | |
120 | effectively the sum of all the contents of the repository for that |
|
120 | effectively the sum of all the contents of the repository for that | |
121 | change, it is impossible in Mercurial to simultaneously commit and add |
|
121 | change, it is impossible in Mercurial to simultaneously commit and add | |
122 | a tag. Thus tagging a revision must be done as a second step. |
|
122 | a tag. Thus tagging a revision must be done as a second step. | |
123 |
|
123 | |||
124 | Q. How do tags work with multiple heads? |
|
124 | ||
|
125 | .Q. How do tags work with multiple heads? | |||
125 |
|
126 | |||
126 | The tags that are in effect at any given time are the tags specified |
|
127 | The tags that are in effect at any given time are the tags specified | |
127 | in each head, with heads closer to the tip taking precedence. |
|
128 | in each head, with heads closer to the tip taking precedence. | |
128 |
|
129 | |||
129 |
|
130 | |||
130 | Q. What are some best practices for distributed development with Mercurial? |
|
131 | .Q. What are some best practices for distributed development with Mercurial? | |
131 |
|
132 | |||
132 | First, merge often! This makes merging easier for everyone and you |
|
133 | First, merge often! This makes merging easier for everyone and you | |
133 | find out about conflicts (which are often rooted in incompatible |
|
134 | find out about conflicts (which are often rooted in incompatible | |
134 | design decisions) earlier. |
|
135 | design decisions) earlier. | |
135 |
|
136 | |||
136 | Second, don't hesitate to use multiple trees locally. Mercurial makes |
|
137 | Second, don't hesitate to use multiple trees locally. Mercurial makes | |
137 | this fast and light-weight. Typical usage is to have an incoming tree, |
|
138 | this fast and light-weight. Typical usage is to have an incoming tree, | |
138 | an outgoing tree, and a separate tree for each area being worked on. |
|
139 | an outgoing tree, and a separate tree for each area being worked on. | |
139 |
|
140 | |||
140 | The incoming tree is best maintained as a pristine copy of the |
|
141 | The incoming tree is best maintained as a pristine copy of the | |
141 | upstream repository. This works as a cache so that you don't have to |
|
142 | upstream repository. This works as a cache so that you don't have to | |
142 | pull multiple copies over the network. No need to check files out here |
|
143 | pull multiple copies over the network. No need to check files out here | |
143 | as you won't be changing them. |
|
144 | as you won't be changing them. | |
144 |
|
145 | |||
145 | The outgoing tree contains all the changes you intend for merger into |
|
146 | The outgoing tree contains all the changes you intend for merger into | |
146 |
upsteam. Publish this tree with 'hg serve |
|
147 | upsteam. Publish this tree with 'hg serve" or hgweb.cgi or use 'hg | |
147 |
push |
|
148 | push" to push it to another publicly availabe repository. | |
148 |
|
149 | |||
149 | Then, for each feature you work on, create a new tree. Commit early |
|
150 | Then, for each feature you work on, create a new tree. Commit early | |
150 | and commit often, merge with incoming regularly, and once you're |
|
151 | and commit often, merge with incoming regularly, and once you're | |
151 | satisfied with your feature, pull the changes into your outgoing tree. |
|
152 | satisfied with your feature, pull the changes into your outgoing tree. | |
152 |
|
153 | |||
153 |
|
154 | |||
154 | Q. How do I import from a repository created in a different SCM? |
|
155 | .Q. How do I import from a repository created in a different SCM? | |
155 |
|
156 | |||
156 | Take a look at contrib/convert-repo. This is an extensible |
|
157 | Take a look at contrib/convert-repo. This is an extensible | |
157 | framework for converting between repository types. |
|
158 | framework for converting between repository types. | |
158 |
|
159 | |||
159 |
|
160 | |||
160 | Q. What about Windows support? |
|
161 | .Q. What about Windows support? | |
161 |
|
162 | |||
162 | Patches to support Windows are being actively integrated, a fully |
|
163 | Patches to support Windows are being actively integrated, a fully | |
163 | working Windows version is probably not far off |
|
164 | working Windows version is probably not far off | |
164 |
|
165 | |||
165 |
|
166 | |||
166 | Section 2: Technical |
|
167 | Section 2: Technical | |
167 | -------------------- |
|
168 | -------------------- | |
168 |
|
169 | |||
169 | Q. What limits does Mercurial have? |
|
170 | .Q. What limits does Mercurial have? | |
170 |
|
171 | |||
171 | Mercurial currently assumes that single files, indices, and manifests |
|
172 | Mercurial currently assumes that single files, indices, and manifests | |
172 | can fit in memory for efficiency. |
|
173 | can fit in memory for efficiency. | |
173 |
|
174 | |||
174 | Offsets in revlogs are currently tracked with 32 bits, so a revlog for |
|
175 | Offsets in revlogs are currently tracked with 32 bits, so a revlog for | |
175 | a single file can currently not grow beyond 4G. |
|
176 | a single file can currently not grow beyond 4G. | |
176 |
|
177 | |||
177 | There should otherwise be no limits on file name length, file size, |
|
178 | There should otherwise be no limits on file name length, file size, | |
178 | file contents, number of files, or number of revisions. |
|
179 | file contents, number of files, or number of revisions. | |
179 |
|
180 | |||
180 | The network protocol is big-endian. |
|
181 | The network protocol is big-endian. | |
181 |
|
182 | |||
182 | File names cannot contain the null character. Committer addresses |
|
183 | File names cannot contain the null character. Committer addresses | |
183 | cannot contain newlines. |
|
184 | cannot contain newlines. | |
184 |
|
185 | |||
185 | Mercurial is primarily developed for UNIX systems, so some UNIXisms |
|
186 | Mercurial is primarily developed for UNIX systems, so some UNIXisms | |
186 | may be present in ports. |
|
187 | may be present in ports. | |
187 |
|
188 | |||
188 |
|
189 | |||
189 | Q. How does signing work? |
|
190 | .Q. How does signing work? | |
190 |
|
191 | |||
191 | Take a look at the hgeditor script for an example. The basic idea |
|
192 | Take a look at the hgeditor script for an example. The basic idea | |
192 | is to sign the manifest ID inside that changelog entry. The manifest |
|
193 | is to sign the manifest ID inside that changelog entry. The manifest | |
193 | ID is a recursive hash of all of the files in the system and their |
|
194 | ID is a recursive hash of all of the files in the system and their | |
194 | complete history, and thus signing the manifest hash signs the entire |
|
195 | complete history, and thus signing the manifest hash signs the entire | |
195 | project to that point. |
|
196 | project to that point. | |
196 |
|
197 | |||
197 | More precisely: each file hash is an SHA1 hash of the contents of that |
|
198 | More precisely: each file hash is an SHA1 hash of the contents of that | |
198 | file and the hashes of its parent revisions. The manifest contains a |
|
199 | file and the hashes of its parent revisions. The manifest contains a | |
199 | list of each file in the project along with its current file hash. |
|
200 | list of each file in the project along with its current file hash. | |
200 | This manifest is hashed similarly to the file hashes, incorporating |
|
201 | This manifest is hashed similarly to the file hashes, incorporating | |
201 | the hashes of the parent revisions. |
|
202 | the hashes of the parent revisions. | |
202 |
|
203 | |||
203 |
|
204 | |||
204 | Q. What about hash collisions? What about weaknesses in SHA1? |
|
205 | .Q. What about hash collisions? What about weaknesses in SHA1? | |
205 |
|
206 | |||
206 | The SHA1 hashes are large enough that the odds of accidental hash collision |
|
207 | The SHA1 hashes are large enough that the odds of accidental hash collision | |
207 | are negligible for projects that could be handled by the human race. |
|
208 | are negligible for projects that could be handled by the human race. | |
208 | The known weaknesses in SHA1 are currently still not practical to |
|
209 | The known weaknesses in SHA1 are currently still not practical to | |
209 | attack, and Mercurial will switch to SHA256 hashing before that |
|
210 | attack, and Mercurial will switch to SHA256 hashing before that | |
210 | becomes a realistic concern. |
|
211 | becomes a realistic concern. | |
211 |
|
212 | |||
212 | Collisions with the "short hashes" are not a concern as they're always |
|
213 | Collisions with the "short hashes" are not a concern as they're always | |
213 | checked for ambiguity and are still long enough that they're not |
|
214 | checked for ambiguity and are still long enough that they're not | |
214 | likely to happen for reasonably-sized projects (< 1M changes). |
|
215 | likely to happen for reasonably-sized projects (< 1M changes). |
General Comments 0
You need to be logged in to leave comments.
Login now