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Basic library for iterating through large ActiveRecord datasets. For instance, let's say you add a new feature, and you need to backfill data for existing records:

iter =, :redis => $redis)
iter.each do |user|

ModelIterator selects the records in batches (100 by default), and loops through the table filtering based on the ID.

SELECT * FROM users WHERE id > 0 LIMIT 100
SELECT * FROM users WHERE id > 100 LIMIT 100
SELECT * FROM users WHERE id > 200 LIMIT 100

Each record's ID is tracked in Redis immediately after being processed. If jobs crash, you can fix code, and re-run from where you left off.

This code was ported from GitHub, where it's been frequently used for nearly two years.

Note on Patches/Pull Requests

  1. Fork the project.
  2. Make your feature addition or bug fix.
  3. Add tests for it. This is important so I don't break it in a future version unintentionally.
  4. Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  5. Send me a pull request. Bonus points for topic branches.