Batched Find

Article.find_each { |a| ... } # => iterate over all articles, in chunks of 1000 (the default)
Article.find_each(:conditions => { :published => true }, :batch_size => 100 ) { |a| ... }
  # iterate over published articles in chunks of 100

Article.find_in_batches { |articles| articles.each { |a| ... } }
  # => articles is array of size 1000
Article.find_in_batches(:batch_size => 100 ) { |articles| articles.each { |a| ... } }
  # iterate over all articles in chunks of 100

class Article < ActiveRecord::Base
  named_scope :published, :conditions => { :published => true }
end

Article.published.find_in_batches(:batch_size => 100 ) { |articles| ... }
  # iterate over published articles in chunks of 100