pessimistic_part_power.py

#!/usr/bin/env python
"""
This script is about telling want you need *today* - not what you want to hear
"""  # noqa
import sys
import math
from argparse import ArgumentParser


parser = ArgumentParser(description=__doc__.lstrip())
parser.add_argument('-R', '--replicas', type=float, default=3.0,
                    help='specify number of replicas or fragments (k+m)')
parser.add_argument('num_devs', type=int, help='number of devices you '
                    'have in the real hardware you are going to deploy')


def best_options(num_devs, replicas):
    reasonable_options = set()
    for i in range(10):
        i += 1
        part_power = int(round(math.log(num_devs * (i * 1000) / replicas, 2)))
        reasonable_options.add(part_power)

    option_map = {}
    for option in sorted(reasonable_options):
        parts_per_dev = int(2 ** option * replicas / num_devs)
        print '@%s number of parts per device is %s' % (
            option, parts_per_dev)
        option_map[option] = parts_per_dev

    middle_of_the_road = sum(option_map.values()) / len(option_map)
    best_options = sorted([
        (abs(middle_of_the_road - per_dev), option)
        for (option, per_dev) in option_map.items()
    ])

    return [option for delta, option in best_options]


def main():
    args = parser.parse_args()
    num_devs = args.num_devs
    replicas = args.replicas

    options = best_options(num_devs, replicas)
    right_answer = options[0]
    print 'If you just use %s, you can easily scale up to...' % right_answer

    max_devices = replicas * (2 ** right_answer) / 100
    thin_nodes = max_devices / 12
    dense_nodes = max_devices / 24
    small_drives = max_devices * replicas
    big_drives = max_devices * 5
    print '%s drives in %s-%s servers storing %s-%s TBs' % tuple(
        int(x) for x in (
            max_devices,
            dense_nodes,
            thin_nodes,
            small_drives,
            big_drives))


if __name__ == "__main__":
    sys.exit(main())