module ActiveRecord module Batches # Looping through a collection of records from the database # (using the +all+ method, for example) is very inefficient # since it will try to instantiate all the objects at once. # # In that case, batch processing methods allow you to work # with the records in batches, thereby greatly reducing memory consumption. # # The #find_each method uses #find_in_batches with a batch size of 1000 (or as # specified by the +:batch_size+ option). # # Person.all.find_each do |person| # person.do_awesome_stuff # end # # Person.where("age > 21").find_each do |person| # person.party_all_night! # end # # You can also pass the +:start+ option to specify # an offset to control the starting point. def find_each(options = {}) find_in_batches(options) do |records| records.each { |record| yield record } end end # Yields each batch of records that was found by the find +options+ as # an array. The size of each batch is set by the +:batch_size+ # option; the default is 1000. # # You can control the starting point for the batch processing by # supplying the +:start+ option. This is especially useful if you # want multiple workers dealing with the same processing queue. You can # make worker 1 handle all the records between id 0 and 10,000 and # worker 2 handle from 10,000 and beyond (by setting the +:start+ # option on that worker). # # It's not possible to set the order. That is automatically set to # ascending on the primary key ("id ASC") to make the batch ordering # work. This also means that this method only works with integer-based # primary keys. You can't set the limit either, that's used to control # the batch sizes. # # Person.where("age > 21").find_in_batches do |group| # sleep(50) # Make sure it doesn't get too crowded in there! # group.each { |person| person.party_all_night! } # end # # # Let's process the next 2000 records # Person.all.find_in_batches(start: 2000, batch_size: 2000) do |group| # group.each { |person| person.party_all_night! } # end def find_in_batches(options = {}) options.assert_valid_keys(:start, :batch_size) relation = self unless arel.orders.blank? && arel.taken.blank? ActiveRecord::Base.logger.warn("Scoped order and limit are ignored, it's forced to be batch order and batch size") end start = options.delete(:start) || 0 batch_size = options.delete(:batch_size) || 1000 relation = relation.reorder(batch_order).limit(batch_size) records = relation.where(table[primary_key].gteq(start)).to_a while records.any? records_size = records.size primary_key_offset = records.last.id yield records break if records_size < batch_size if primary_key_offset records = relation.where(table[primary_key].gt(primary_key_offset)).to_a else raise "Primary key not included in the custom select clause" end end end private def batch_order "#{quoted_table_name}.#{quoted_primary_key} ASC" end end end