Compare PostgreSQL LSN in ruby

compare-pg-lsn.rb

# select pg_xlog_location_diff('951A/EA0F8000', '9518/1ECB6000');
# super_db=# select pg_xlog_location_diff('951A/EA0F8000', '9518/1ECB6000');
#  pg_xlog_location_diff
# -----------------------
#            12000174080
# (1 row)

# super_db=# select pg_xlogfile_name('951A/EA0F8000'), pg_xlogfile_name('9518/1ECB6000');
# -[ RECORD 1 ]----+-------------------------
# pg_xlogfile_name | 000000030000951A000000EA
# pg_xlogfile_name | 00000003000095180000001E

class String
    def trim_lead(n)
        self.gsub!(/^#{n}+/,'')
    end
end

def to_lsn lsn
    timeline, logfile, offset =  lsn.scan(/.{8}/)

    "#{logfile.trim_lead("0")}/#{offset.trim_lead("0").ljust(8, "0")}"
end

def to_bytes lsn
    file, pos = lsn.split('/')

    ('FFFFFFFF'.hex * file.hex + pos.hex)
end

def compare_lsn master_lsn, slave_lsn 
    ( to_bytes(master_lsn) + 2) - to_bytes(slave_lsn)
end

# puts compare_lsn '951A/EA0F8000', '9518/1ECB6000'
# first = to_lsn '000000030000951A000000EA'
# second = to_lsn '00000003000095180000001E'


# puts "select pg_xlogfile_name('#{first}'), pg_xlogfile_name('#{second}');"
# puts "select pg_xlog_location_diff('#{first}','#{second}');"


### computed: 12012486656
### correct : 12000174080


require 'optparse'

options = {
    :compare_wal => false,
    :origin_input => "",
    :destiny_input => "",
}

OptionParser.new do |opts|
  opts.banner = "Usage: replication_diff.rb [options]"
  opts.separator ""
  opts.separator "General options:"

  opts.on "-w", "--wal", "compare walfiles and compute the LSN" do |v|
    options[:compare_wal] = true
  end

  opts.on "-o", "--origin VALUE", "origin wal file (or LSN)" do |v|
    options[:origin_input] = v
  end

  opts.on "-d", "--destiny VALUE", "destiny wal file (or LSN)" do |v|
    options[:destiny_input] = v
  end

end.parse!

if options[:compare_wal]
    first = to_lsn options[:origin_input]
    second = to_lsn options[:destiny_input]
else
    first = options[:origin_input]
    second = options[:destiny_input]
end

puts compare_lsn first, second