helpers.rb

#
# Cookbook Name:: postgresql
# Library:: helpers
#
# Copyright 2010, Estately, Inc.
#
# All rights reserved - Do Not Redistribute
#

module Foo

  class << self
    # postgresql.conf allows you to set values using numbers (in bytes) or
    # strings ending in kB, MB, or GB. This method takes any of those values
    # and converts it to bytes.
    def translate_size( size )
      return size if size.is_a? Numeric

      value, units = size.match( /^(\d+)(\w+)$/ )[1,2]

      case units
      when "kB"
        return value * 1024
      when "MB"
        return value * 1_048_576
      when "GB"
        return value * 1_073_741_824
      end
    end

    # based on the information contained in table 17-2 in the postgres
    # manual.
    #
    # http://www.postgresql.org/docs/8.4/static/kernel-resources.html
    def calculate_shmmax
      requirements = []

      # we'll be using this again...
      mlpt = translate_size( node.max_locks_per_transaction )

      # base memory
      requirements << translate_size( "770kB" )

      # memory per connection
      requirements << (1800 + 270 * mlpt) * node.max_connections

      # memory per autovacuum worker
      requirements << (1800 + 270 * mlpt) * node.autovacuum_max_workers

      # memory per prepared transaction
      requirement << (770 + 270 * mlpt) * node.max_prepared_transactions

      # shared disk buffers
      requirements << (node.block_size + 208) * translate_size(node.shared_buffers)

      # WAL buffers
      requirements << (node.wal_block_size + 8) * translate_size(node.wal_buffers)

      return requirements.inject(0) {|sum, value| sum += value }
    end
  end
end

# Foo.calculate_shmmax