epriestley e0b86cc81b Add a Mercurial commit discovery daemon ... Summary: Repository import has three major steps: - Commit discovery (serial) - Message parsing (parallel, mostly VCS independent) - Change parsing (parallel, highly VCS dependent) This implements commit discovery for Mercurial, similar to git's parsing: - List the heads of all the branches. - If we haven't already discovered them, follow them back to their roots (or the first commit we have discovered). - Import all the newly discovered commits, oldest first. This is a little complicated but it ensures we discover commits in depth order, so the discovery process is robust against interruption/failure. If we just inserted commits as we went, we might read the tip, insert it, and then crash. When we ran again, we'd think we had already discovered commits older than HEAD. This also allows later stages to rely on being able to find Phabricator commit IDs which correspond to parent commits. NOTE: This importer is fairly slow because "hg" has a large startup time (compare "hg --version" to "git --version" and "svn --version"; on my machine, hg has 60ms of overhead for any command) and we need to run many commands (see the whole "hg id" mess). You can expect something like 10,000 per hour, which means you may need to run overnight to discover a large repository (IIRC, the svn/git discovery processes are both about an order of magnitude faster). We could improve this with batching, but I want to keep it as simple as possible for now. Test Plan: Discovered all the commits in the main Mercurial repository, http://selenic.com/repo/hg. Reviewers: Makinde, jungejason, nh, tuomaspelkonen, aran Reviewed By: Makinde CC: aran, Makinde Differential Revision: 943		2011-09-16 11:08:52 -07:00
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phabricator_daemon_launcher.php	Add a Mercurial commit discovery daemon	2011-09-16 11:08:52 -07:00