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Module: ActiveRecord::Batches

Constant Summary

Instance Method Summary

Instance Method Details

#act_on_ignored_order(error_on_ignore) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 369

def act_on_ignored_order(error_on_ignore)
  raise_error = (error_on_ignore.nil? ? ActiveRecord.error_on_ignored_order : error_on_ignore)

  if raise_error
    raise ArgumentError.new(ORDER_IGNORE_MESSAGE)
  elsif model.logger
    model.logger.warn(ORDER_IGNORE_MESSAGE)
  end
end

#apply_finish_limit(relation, cursor, finish, batch_orders) (private)

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# File 'activerecord/lib/active_record/relation/batches.rb', line 341

def apply_finish_limit(relation, cursor, finish, batch_orders)
  operators = batch_orders.map do |_column, order|
    order == :desc ? :gteq : :lteq
  end
  batch_condition(relation, cursor, finish, operators)
end

#apply_limits(relation, cursor, start, finish, batch_orders) (private)

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# File 'activerecord/lib/active_record/relation/batches.rb', line 328

def apply_limits(relation, cursor, start, finish, batch_orders)
  relation = apply_start_limit(relation, cursor, start, batch_orders) if start
  relation = apply_finish_limit(relation, cursor, finish, batch_orders) if finish
  relation
end

#apply_start_limit(relation, cursor, start, batch_orders) (private)

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# File 'activerecord/lib/active_record/relation/batches.rb', line 334

def apply_start_limit(relation, cursor, start, batch_orders)
  operators = batch_orders.map do |_column, order|
    order == :desc ? :lteq : :gteq
  end
  batch_condition(relation, cursor, start, operators)
end

#batch_condition(relation, cursor, values, operators) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 348

def batch_condition(relation, cursor, values, operators)
  cursor_positions = cursor.zip(Array(values), operators)

  first_clause_column, first_clause_value, operator = cursor_positions.pop
  where_clause = predicate_builder[first_clause_column, first_clause_value, operator]

  cursor_positions.reverse_each do |column_name, value, operator|
    where_clause = predicate_builder[column_name, value, operator == :lteq ? :lt : :gt].or(
      predicate_builder[column_name, value, :eq].and(where_clause)
    )
  end

  relation.where(where_clause)
end

#batch_on_loaded_relation(relation:, start:, finish:, cursor:, order:, batch_limit:) (private)

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# File 'activerecord/lib/active_record/relation/batches.rb', line 379

def batch_on_loaded_relation(relation:, start:, finish:, cursor:, order:, batch_limit:)
  records = relation.to_a
  order = build_batch_orders(cursor, order).map(&:second)

  if start || finish
    records = records.filter do |record|
      values = record_cursor_values(record, cursor)

      (start.nil? || compare_values_for_order(values, Array(start), order) >= 0) &&
        (finish.nil? || compare_values_for_order(values, Array(finish), order) <= 0)
    end
  end

  records.sort! do |record1, record2|
    values1 = record_cursor_values(record1, cursor)
    values2 = record_cursor_values(record2, cursor)
    compare_values_for_order(values1, values2, order)
  end

  records.each_slice(batch_limit) do |subrecords|
    subrelation = relation.spawn
    subrelation.load_records(subrecords)

    yield subrelation
  end

  nil
end

#batch_on_unloaded_relation(relation:, start:, finish:, load:, cursor:, order:, use_ranges:, remaining:, batch_limit:) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 426

def batch_on_unloaded_relation(relation:, start:, finish:, load:, cursor:, order:, use_ranges:, remaining:, batch_limit:)
  batch_orders = build_batch_orders(cursor, order)
  relation = relation.reorder(batch_orders.to_h).limit(batch_limit)
  relation = apply_limits(relation, cursor, start, finish, batch_orders)
  relation.skip_query_cache! # Retaining the results in the query cache would undermine the point of batching
  batch_relation = relation
  empty_scope = to_sql == model.unscoped.all.to_sql

  loop do
    if load
      records = batch_relation.records
      values = records.pluck(*cursor)
      yielded_relation = where(cursor => values)
      yielded_relation.load_records(records)
    elsif (empty_scope && use_ranges != false) || use_ranges
      values = batch_relation.pluck(*cursor)

      finish = values.last
      if finish
        yielded_relation = apply_finish_limit(batch_relation, cursor, finish, batch_orders)
        yielded_relation = yielded_relation.except(:limit, :order)
        yielded_relation.skip_query_cache!(false)
      end
    else
      values = batch_relation.pluck(*cursor)
      yielded_relation = where(cursor => values)
    end

    break if values.empty?

    if values.flatten.any?(nil)
      raise ArgumentError, "Not all of the batch cursor columns were included in the custom select clause "\
                            "or some columns contain nil."
    end

    yield yielded_relation

    break if values.length < batch_limit

    if limit_value
      remaining -= values.length

      if remaining == 0
        # Saves a useless iteration when the limit is a multiple of the
        # batch size.
        break
      elsif remaining < batch_limit
        relation = relation.limit(remaining)
      end
    end

    batch_orders_copy = batch_orders.dup
    _last_column, last_order = batch_orders_copy.pop
    operators = batch_orders_copy.map do |_column, order|
      order == :desc ? :lteq : :gteq
    end
    operators << (last_order == :desc ? :lt : :gt)

    cursor_value = values.last
    batch_relation = batch_condition(relation, cursor, cursor_value, operators)
  end

  nil
end

#build_batch_orders(cursor, order) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 363

def build_batch_orders(cursor, order)
  cursor.zip(Array(order)).map do |column, order_|
    [column, order_ || DEFAULT_ORDER]
  end
end

#compare_values_for_order(values1, values2, order) (private)

This is a custom implementation of <=> operator, which also takes into account how the collection will be ordered.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 414

def compare_values_for_order(values1, values2, order)
  values1.each_with_index do |element1, index|
    element2 = values2[index]
    direction = order[index]
    comparison = element1 <=> element2
    comparison = -comparison if direction == :desc
    return comparison if comparison != 0
  end

  0
end

#ensure_valid_options_for_batching!(cursor, start, finish, order) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 305

def ensure_valid_options_for_batching!(cursor, start, finish, order)
  if start && Array(start).size != cursor.size
    raise ArgumentError, ":start must contain one value per cursor column"
  end

  if finish && Array(finish).size != cursor.size
    raise ArgumentError, ":finish must contain one value per cursor column"
  end

  if (Array(primary_key) - cursor).any?
    indexes = model.schema_cache.indexes(table_name)
    unique_index = indexes.find { |index| index.unique && index.where.nil? && (Array(index.columns) - cursor).empty? }

    unless unique_index
      raise ArgumentError, ":cursor must include a primary key or other unique column(s)"
    end
  end

  if (Array(order) - [:asc, :desc]).any?
    raise ArgumentError, ":order must be :asc or :desc or an array consisting of :asc or :desc, got #{order.inspect}"
  end
end

#find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, &block)

Looping through a collection of records from the database (using the Scoping::Named::ClassMethods#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.find_each do |person|
  person.do_awesome_stuff
end

Person.where("age > 21").find_each do |person|
  person.party_all_night!
end

If you do not provide a block to #find_each, it will return an Enumerator for chaining with other methods:

Person.find_each.with_index do |person, index|
  person.award_trophy(index + 1)
end

Options

  • :batch_size - Specifies the size of the batch. Defaults to 1000.

  • :start - Specifies the cursor column value to start from, inclusive of the value.

  • :finish - Specifies the cursor column value to end at, inclusive of the value.

  • :error_on_ignore - Overrides the application config to specify if an error should be raised when an order is present in the relation.

  • :cursor - Specifies the column to use for batching (can be a column name or an array of column names). Defaults to primary key.

  • :order - Specifies the cursor column order (can be :asc or :desc or an array consisting of :asc or :desc). Defaults to :asc.

    class Order < ActiveRecord::Base
      self.primary_key = [:id_1, :id_2]
    end
    
    Order.find_each(order: [:asc, :desc])

    In the above code, id_1 is sorted in ascending order and id_2 in descending order.

Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.

The options start and finish are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start and :finish option on each worker.

# In worker 1, let's process until 9999 records.
Person.find_each(finish: 9_999) do |person|
  person.party_all_night!
end

# In worker 2, let's process from record 10_000 and onwards.
Person.find_each(start: 10_000) do |person|
  person.party_all_night!
end

NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to ascending on the primary key (“id ASC”). This also means that this method only works when the cursor column is orderable (e.g. an integer or string).

NOTE: When using custom columns for batching, they should include at least one unique column (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions, all columns should be static (unchangeable after it was set).

NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 85

def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, &block)
  if block_given?
    find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do |records|
      records.each(&block)
    end
  else
    enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do
      relation = self
      cursor = Array(cursor)
      apply_limits(relation, cursor, start, finish, build_batch_orders(cursor, order)).size
    end
  end
end

#find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER)

Yields each batch of records that was found by the find options as an array.

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

If you do not provide a block to #find_in_batches, it will return an Enumerator for chaining with other methods:

Person.find_in_batches.with_index do |group, batch|
  puts "Processing group ##{batch}"
  group.each(&:recover_from_last_night!)
end

To be yielded each record one by one, use #find_each instead.

Options

  • :batch_size - Specifies the size of the batch. Defaults to 1000.

  • :start - Specifies the cursor column value to start from, inclusive of the value.

  • :finish - Specifies the cursor column value to end at, inclusive of the value.

  • :error_on_ignore - Overrides the application config to specify if an error should be raised when an order is present in the relation.

  • :cursor - Specifies the column to use for batching (can be a column name or an array of column names). Defaults to primary key.

  • :order - Specifies the cursor column order (can be :asc or :desc or an array consisting of :asc or :desc). Defaults to :asc.

    class Order < ActiveRecord::Base
      self.primary_key = [:id_1, :id_2]
    end
    
    Order.find_in_batches(order: [:asc, :desc])

    In the above code, id_1 is sorted in ascending order and id_2 in descending order.

Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.

The options start and finish are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start and :finish option on each worker.

# Let's process from record 10_000 on.
Person.find_in_batches(start: 10_000) do |group|
  group.each { |person| person.party_all_night! }
end

NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to ascending on the primary key (“id ASC”). This also means that this method only works when the cursor column is orderable (e.g. an integer or string).

NOTE: When using custom columns for batching, they should include at least one unique column (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions, all columns should be static (unchangeable after it was set).

NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 161

def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER)
  relation = self
  unless block_given?
    return to_enum(:find_in_batches, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do
      cursor = Array(cursor)
      total = apply_limits(relation, cursor, start, finish, build_batch_orders(cursor, order)).size
      (total - 1).div(batch_size) + 1
    end
  end

  in_batches(of: batch_size, start: start, finish: finish, load: true, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do |batch|
    yield batch.to_a
  end
end

#in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, use_ranges: nil, &block)

Yields Relation objects to work with a batch of records.

Person.where("age > 21").in_batches do |relation|
  relation.delete_all
  sleep(10) # Throttle the delete queries
end

If you do not provide a block to #in_batches, it will return a Batches::BatchEnumerator which is enumerable.

Person.in_batches.each_with_index do |relation, batch_index|
  puts "Processing relation ##{batch_index}"
  relation.delete_all
end

Examples of calling methods on the returned Batches::BatchEnumerator object:

Person.in_batches.delete_all
Person.in_batches.update_all(awesome: true)
Person.in_batches.each_record(&:party_all_night!)

Options

  • :of - Specifies the size of the batch. Defaults to 1000.

  • :load - Specifies if the relation should be loaded. Defaults to false.

  • :start - Specifies the cursor column value to start from, inclusive of the value.

  • :finish - Specifies the cursor column value to end at, inclusive of the value.

  • :error_on_ignore - Overrides the application config to specify if an error should be raised when an order is present in the relation.

  • :cursor - Specifies the column to use for batching (can be a column name or an array of column names). Defaults to primary key.

  • :order - Specifies the cursor column order (can be :asc or :desc or an array consisting of :asc or :desc). Defaults to :asc.

    class Order < ActiveRecord::Base
      self.primary_key = [:id_1, :id_2]
    end
    
    Order.in_batches(order: [:asc, :desc])

    In the above code, id_1 is sorted in ascending order and id_2 in descending order.

  • :use_ranges - Specifies whether to use range iteration (id >= x AND id <= y). It can make iterating over the whole or almost whole tables several times faster. Only whole table iterations use this style of iteration by default. You can disable this behavior by passing false. If you iterate over the table and the only condition is, e.g., archived_at: nil (and only a tiny fraction of the records are archived), it makes sense to opt in to this approach.

Limits are honored, and if present there is no requirement for the batch size, it can be less than, equal, or greater than the limit.

The options start and finish are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start and :finish option on each worker.

# Let's process from record 10_000 on.
Person.in_batches(start: 10_000).update_all(awesome: true)

An example of calling where query method on the relation:

Person.in_batches.each do |relation|
  relation.update_all('age = age + 1')
  relation.where('age > 21').update_all(should_party: true)
  relation.where('age <= 21').delete_all
end

NOTE: If you are going to iterate through each record, you should call #each_record on the yielded Batches::BatchEnumerator:

Person.in_batches.each_record(&:party_all_night!)

NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to ascending on the primary key (“id ASC”). This also means that this method only works when the cursor column is orderable (e.g. an integer or string).

NOTE: When using custom columns for batching, they should include at least one unique column (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions, all columns should be static (unchangeable after it was set).

NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 259

def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, use_ranges: nil, &block)
  cursor = Array(cursor).map(&:to_s)
  ensure_valid_options_for_batching!(cursor, start, finish, order)

  if arel.orders.present?
    act_on_ignored_order(error_on_ignore)
  end

  unless block
    return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self, cursor: cursor, order: order, use_ranges: use_ranges)
  end

  batch_limit = of

  if limit_value
    remaining   = limit_value
    batch_limit = remaining if remaining < batch_limit
  end

  if self.loaded?
    batch_on_loaded_relation(
      relation: self,
      start: start,
      finish: finish,
      cursor: cursor,
      order: order,
      batch_limit: batch_limit,
      &block
    )
  else
    batch_on_unloaded_relation(
      relation: self,
      start: start,
      finish: finish,
      load: load,
      cursor: cursor,
      order: order,
      use_ranges: use_ranges,
      remaining: remaining,
      batch_limit: batch_limit,
      &block
    )
  end
end

#record_cursor_values(record, cursor) (private)

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/batches.rb', line 408

def record_cursor_values(record, cursor)
  record.attributes.slice(*cursor).values
end