auto_tagger and alternate tag refs

June 22, 2011 Pivotal Labs

A recent addition to Jeff Dean’s auto_tagger is the ability to use an alternate tag ref type instead of standard git tags. I pestered Jeff to add this feature after Scott Chacon explained to me how bad it is to create a large number of tags in git. Thanks, Jeff, for the feature addition!

There are a couple problems with generating autotags as standard git tags. One is that it pollutes the tag namespace which makes it harder to find tags for releases, etc. And it defeats the tags menu in the GitHub UI. The other is that git will automatically sync tags on every fetch and push, which can noticeably slow things down when you have a lot of tags. And it looks like running GitX with thousands of tags can make the app seriously slow and prone to crash.

A little background: A git tag is just a kind of ref in a special namespace. A ref is a file that contains a SHA-1 has identifying a commit, and is an entry point into the big network of blobs in the git object database. It’s quite easy to create new kinds of refs; you just put a new directory in the .git/refs dir and go from there. auto_tagger will now do this for you simply by adding one configuration option.

Drop a .auto_tagger options file into your project with these contents:

--ref-path=autotags

auto_tagger will automatically fetch and push tags in a custom namespace when it needs to. You almost never need to look at autotag refs in development, but if you do, you may need to fetch them manually. That’s part of the point of using an alternate tag type, avoiding syncing them automatically on every fetch. To manually fetch all the autotags (when using the ref-path=autotags option as above), do

$ git fetch origin refs/autotags/*:refs/autotags/*

I also really like the auto_tagger option to format tag names so they are human readable timestamps by adding a separator character. To make that work, set the date-separator option. Your .auto_tagger options file should look like:

--ref-path=autotags
--date-separator=-

Then your autotags look like “ci/2010-10-09-00-56-21” instead of “ci/20101009005621”

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