Mercurial > hgsubversion
view notes/metadata.txt @ 890:78db88de9622
Partial metadata rebuilding
For highly active subversion repositories, it can be excruciatingly
slow to pull updates one at a time from subversion. One way around
this is to setup another mercurial repo that pulls new commits from
svn periodicly (say every 5 minutes). When you want to update your
repository, you can pull commits from this mercurial repository via
native mercurial protocols, which will be much faster than pulling
directly from svn.
Unfortunately, your metadata will be out of date after doing so.
Highly active repositories also tend to be very large, which means
that it takes a long time to rebuild your metadata from scratch. To
address this, this adds support to do a partial rebuild on the
metadata by processing only revisions that have been added to the
repository after the last revision we processed.
With the rev map 1k revisions (~2 days) behind tip updatemeta is
dramatically faster than rebuild meta:
$ hg --time svn updatemeta
Time: real 0.570 secs (user 0.480+0.000 sys 0.060+0.000)
$ hg --time svn rebuildmeta
Time: real 129.160 secs (user 128.570+0.000 sys 0.320+0.000)
author | David Schleimer <dschleimer@fb.com> |
---|---|
date | Sat, 12 May 2012 07:28:23 -0700 |
parents | ba801f44d240 |
children |
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Branches -------- In order to handle branches that are not immediate children of /branches/, the following information must be stored in the revmap: revision path Where path is the actual relative path of the branch in svn. An example, with the previous format for clarification: New | Old 3 <hash> trunk | 3 <hash> 4 <hash> branches/foo | 4 <hash> foo Tags ---- Note that if a tag is committed to, we can handle that case by making a branch and then marking it as deleted. The revmap line would look something like this: 10 <hash> tags/the_tag And the commit would be done on the hg branch 'modified-tag/the_tag'. Note that if this was 'tags/releases/1.0.0', then the branch would be 'modified-tag/releases/1.0.0'. Detecting Closing of Branches ----------------------------- Subversion users typically remove branches when done with them. This means that if a commit performs a delete operation on the '' path inside a branch, we can be sure that the branch no longer exists. The branch should then be marked as inactive. Closing Branches ---------------- As of this writing, Mercurial marks branches as inactive by merging them so they have no active heads. In order to mark a branch as closed, the active head on the branch will be used as the first parent of the new changeset, and the second changeset will be either the active head on the hg branch 'closed-branches' or be the nullrev. The commit to mark the branch as inactive will happen on the 'closed-branches' branch in Mercurial. Recovery -------- hgsubversion stores several pieces of essential metadata in .hg/svn/. In order to rebuild this data, the key 'convert_revision' should be stored in the extra dictionary of the converted revision. The key should contain data in the format: 'svn:<uuid>/abs/path@<rev>' where <uuid> is the repo UUID, /abs/path is the absolute path to the location the edits were made in Subversion (that is, if it was a trunk commit on /foo/trunk, then /foo/trunk is what gets stored here, even though the project root does not equal the repo root), and <rev> is the revision number of the change in Subversion. This key (and its contents) have been chosen to be compatible with the convert extension so that repos originally converted to hg using convert can be maintained using hgsubversion if desired. Tags (tag_info) can be reconstructed by listing the tags directory and then running log on each tag to determine its parent changeset. The last revision converted (last_rev) can be converted simply by using the highest revision number encountered while rebuilding the revision map. The legacy tag_locations file does not need to be replaced - it will be obsoleted as part of the long-term branch refactor. The url will have to be provided by the user. The uuid can be re-requested from the repository. branch_info can be rebuilt during the rebuild of the revision map by recording the revisions of all active heads of server-side branches. branch_info contains a map from branch: (parent_branch, parent_branch_rev, branch_created_rev)