Module: CassandraModel::Batches::ClassMethods

Defined in:
lib/cassandra-model/batches.rb

Overview

When processing large numbers of records, it’s often a good idea to do so in batches to prevent memory ballooning.

Instance Method Summary collapse

Instance Method Details

#find_each(options = {}) ⇒ Object

Yields each record that was found by the find options. The find is performed by find_in_batches with a batch size of 1000 (or as specified by the :batch_size option).

Example:

Person.find_each(:conditions => "age > 21") do |person|
  person.party_all_night!
end

Note: This method is only intended to use for batch processing of large amounts of records that wouldn’t fit in memory all at once. If you just need to loop over less than 1000 records, it’s probably better just to use the regular find methods.



25
26
27
28
29
30
31
 
# File 'lib/cassandra-model/batches.rb', line 25

def find_each(options = {})
  find_in_batches(options) do |records|
    records.each { |record| yield record }
  end

  self
end

#find_in_batches(options = {}) ⇒ Object

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 mean that this method only works with integer-based primary keys. You can’t set the limit either, that’s used to control the the batch sizes.

Example:

Person.find_in_batches(:conditions => "age > 21") do |group|
  sleep(50) # Make sure it doesn't get too crowded in there!
  group.each { |person| person.party_all_night! }
end



56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
 
# File 'lib/cassandra-model/batches.rb', line 56

def find_in_batches(options = {})
  raise "You can't specify an order." if options[:order]
  raise "You can't specify a limit, it's forced to be the batch_size"  if options[:limit]

  start = options.delete(:start) || ''
  nofilter = options[:no_filter]
  batch_size = options.delete(:batch_size) || 500

  records = self.find(:all, :keyrange => start..'', :limit => batch_size)

  while records.any?
    count = records.size
    records = filter_deleted(records) unless nofilter
    yield records
    break if count < batch_size

    last_value = records.last.id
    records = self.find(:all, :keyrange => last_value..'', :limit => batch_size)
  end
end