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annotate notes/metadata.txt @ 225:2117cb0118fe

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Get rid of .hg/svn/last_rev: We now calculate the last known revision by iterating over all known revisions and finding the highest number. Theoretically, we might be able to simply read the latest entry, but in practice, that's a bug waiting to happen. For instance, we might want to achieve compatibility with '.hg/shamap' as generated by the ConvertExtension, and it not only cannot offer a guarantee of linearity, but it also allows more than one conversion to source exists. I'd say we have other problems to care about until this turns up as a hotspot in profiling. Such as why we leak circa 100MB of memory per 1000 revisions converted ;)
author Dan Villiom Podlaski Christiansen <danchr@gmail.com>
date Fri, 27 Mar 2009 01:09:36 +0100
parents ba801f44d240
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 Branches
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2 --------
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3 In order to handle branches that are not immediate children of /branches/, the
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4 following information must be stored in the revmap:
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5
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6 revision path
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7
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8 Where path is the actual relative path of the branch in svn. An example, with
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9 the previous format for clarification:
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10 New | Old
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11 3 <hash> trunk | 3 <hash>
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12 4 <hash> branches/foo | 4 <hash> foo
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13
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14 Tags
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15 ----
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16 Note that if a tag is committed to, we can handle that case by making a branch
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17 and then marking it as deleted. The revmap line would look something like this:
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18 10 <hash> tags/the_tag
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19 And the commit would be done on the hg branch 'modified-tag/the_tag'. Note that
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20 if this was 'tags/releases/1.0.0', then the branch would be
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21 'modified-tag/releases/1.0.0'.
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22
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23 Detecting Closing of Branches
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24 -----------------------------
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25 Subversion users typically remove branches when done with them. This means that
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26 if a commit performs a delete operation on the '' path inside a branch, we can
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27 be sure that the branch no longer exists. The branch should then be marked as
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28 inactive.
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29
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30 Closing Branches
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31 ----------------
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32 As of this writing, Mercurial marks branches as inactive by merging them so they
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33 have no active heads. In order to mark a branch as closed, the active head on
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34 the branch will be used as the first parent of the new changeset, and the second
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35 changeset will be either the active head on the hg branch 'closed-branches' or
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36 be the nullrev. The commit to mark the branch as inactive will happen on the
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37 'closed-branches' branch in Mercurial.
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38
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39 Recovery
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40 --------
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41 hgsubversion stores several pieces of essential metadata in .hg/svn/. In order
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42 to rebuild this data, the key 'convert_revision' should be stored in the extra
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43 dictionary of the converted revision. The key should contain data in the format:
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44 'svn:<uuid>/abs/path@<rev>' where <uuid> is the repo UUID, /abs/path is the
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45 absolute path to the location the edits were made in Subversion (that is, if it
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46 was a trunk commit on /foo/trunk, then /foo/trunk is what gets stored here, even
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47 though the project root does not equal the repo root), and <rev> is the revision
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48 number of the change in Subversion. This key (and its contents) have been
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49 chosen to be compatible with the convert extension so that repos originally
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50 converted to hg using convert can be maintained using hgsubversion if desired.
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51
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52 Tags (tag_info) can be reconstructed by listing the tags directory and then
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53 running log on each tag to determine its parent changeset.
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54
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55 The last revision converted (last_rev) can be converted simply by using the
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56 highest revision number encountered while rebuilding the revision map.
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57
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58 The legacy tag_locations file does not need to be replaced - it will be
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59 obsoleted as part of the long-term branch refactor.
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60
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61 The url will have to be provided by the user. The uuid can be re-requested from
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62 the repository.
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63
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64 branch_info can be rebuilt during the rebuild of the revision map by recording
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65 the revisions of all active heads of server-side branches. branch_info contains
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66 a map from branch: (parent_branch, parent_branch_rev, branch_created_rev)