splitter.rb

# TableSplitter splits record ids up into ranges to use in SQL

#!/usr/bin/env ruby
require File.dirname(__FILE__) + '/../config/environment'

# $ ./splitter.rb 5 2
# break into 5 chunks.
# requesting chunk 2: id >= 74 and id < 144
# For demo purposes, here are all of them:
# requesting chunk 1: id >= 1 and id < 74
# requesting chunk 2: id >= 74 and id < 144
# requesting chunk 3: id >= 144 and id < 215
# requesting chunk 4: id >= 215 and id < 285
# requesting chunk 5: id > 285

class TableSplitter
	def initialize (table, num_chunks)
		@table = table
		@num_chunks = num_chunks
		@c = []
		split()
	end

  def split()
    sql = "select id from #{@table}"
    ids = ActiveRecord::Base.connection.select_values(sql).collect! { |x| x.to_i }
    size = ids.size
    ids.sort!
    chunk_size = (size/@num_chunks).floor

    marker = 0
    @num_chunks.times do |t|
      @c[t] = ids[marker]
      marker = marker + chunk_size
    end
  end
  
  def chunk(num)
    if (@num_chunks == num)
      result = "id > #{@c[-1]}"  # leave the end range open
    else
      result = "id >= #{@c[num-1]} and id < #{@c[num]}"
    end
    result   
  end
end

chunks = ARGV[0].to_i   # the number of pieces to break it up into
chunk  = ARGV[1].to_i   # which chunk do you want?

if ( ( ARGV.size != 2 ) || (chunk > chunks) )
  raise "splitter.rb [chunksize] [chunknumber]"
end

puts "break into #{chunks} chunks."

splitter = TableSplitter.new("users", chunks)

puts "requesting chunk #{chunk}: #{splitter.chunk(chunk)}"

puts "For demo purposes, here are all of them:"
chunks.times do |t|
  puts "requesting chunk #{t+1}: #{splitter.chunk(t+1)}"
end