On-the-fly index rotation

tire_ext.rb

module Tire
  def self.inverted_aliases
    aliases.inject({}) do |acc, (index, aliases)|
      aliases.each do |als|
        acc[als] ||= SortedSet.new
        acc[als] << index
      end
      acc
    end
  end

  def self.reindex(klass, options = {})
    scope = options[:scope] || klass.scoped

    index_alias = klass.index_name

    # Alias-based reindexing when already having a real index is an error state
    if Tire.index(index_alias).exists? && !Tire.inverted_aliases[index_alias]
      raise "#{klass.index_name} exists and is not an alias"
    end

    # First, populate the new index
    new_index_name = Time.now.strftime("%Y%m%d_%H%M%S")
    new_index = Tire.index(new_index_name)
    new_index.create(:mappings => klass.mapping_to_hash,
                     :settings => klass.settings)
    scope.find_in_batches do |batch|
      new_index.import batch
    end

    # Create an alias to the new index, so Klass.index points to both
    # (elasticsearch supports one alias to many indexes)
    new_index.add_alias(index_alias)

    # Delete old index
    old_index_name = Tire.inverted_aliases[index_alias].first
    unless old_index_name == new_index_name
      old_index = Tire.index(old_index_name)
      old_index.remove_alias(index_alias)
      old_index.delete
    end

    true
  end
end