#!/usr/bin/python3

# Copyright 2017 Facebook.

# Licensed under the same terms as memcached itself.

import argparse

import socket

import sys

import re

import traceback

from time import sleep

parser = argparse.ArgumentParser(description="daemon for rebalancing slabs")

parser.add_argument("--host", help="host to connect to",

        default="localhost:11211", metavar="HOST:PORT")

parser.add_argument("-s", "--sleep", help="seconds between runs",

                    type=int, default="1")

parser.add_argument("-v", "--verbose", action="store_true")

parser.add_argument("-a", "--automove", action="store_true", default=False,

                    help="enable automatic page rebalancing")

parser.add_argument("-w", "--window", type=int, default="30",

                    help="rolling window size for decision history")

parser.add_argument("-r", "--ratio", type=float, default=0.8,

                    help="ratio limiting distance between low/high class ages")

# TODO:

# - age adjuster function

#   - by ratio of get_hits

#   - by ratio of chunk size

args = parser.parse_args()

host, port = args.host.split(':')

def window_check(history, sid, key):

    total = 0

    for window in history['w']:

        s = window.get(sid)

        if s and s.get(key):

            total += s.get(key)

    return total

def determine_move(history, diffs, totals):

    """ Figure out of a page move is in order.

    - if > 2.5 pages of free space without free chunks reducing for N trials,

      and no evictions for N trials, free to global.

    - use ratio of how far apart age can be between slab classes

    - TODO: if get_hits exists, allowable distance in age from the *youngest* slab

      class is based on the percentage of get_hits the class gets, against the

      factored max distance, ie:

      1% max delta. youngest is 900, oldest allowable is 900+90

      if class has 30% of get_hits, it can be 930

    - youngest evicting slab class gets page moved to it, if outside ratio max

    - use age as average over window. smooths over items falling out of WARM.

      also gives a little weight: if still evicting, a few more pages than

      necessary may be moved, pulling the classes closer together. Hopefully

      avoiding ping-ponging.

    """

    # rotate windows

    history['w'].append({})

    if (len(history['w']) > args.window):

        history['w'].pop(0)

    w = history['w'][-1]

    oldest = (-1, 0)

    youngest = (-1, sys.maxsize)

    decision = (-1, -1)

    for sid, slab in diffs.items():

        w[sid] = {}

        if 'evicted_d' not in slab or 'total_pages_d' not in slab:

            continue

        # mark this window as dirty if total pages increases or evictions

        # happened

        if slab['total_pages_d'] > 0:

            w[sid]['dirty'] = 1

        if slab['evicted_d'] > 0:

            w[sid]['dirty'] = 1

            w[sid]['ev'] = 1

        w[sid]['age'] = slab['age']

        age = window_check(history, sid, 'age') / len(history['w'])

        # if > 2.5 pages free, and not dirty, reassign to global page pool and

        # break.

        if slab['free_chunks'] > slab['chunks_per_page'] * 2.5:

            if window_check(history, sid, 'dirty') == 0:

                decision = (sid, 0)

                break

        # are we the oldest slab class? (and a valid target)

        if age > oldest[1] and slab['total_pages'] > 2:

            oldest = (sid, age)

        # are we the youngest evicting slab class?

        ev_total = window_check(history, sid, 'ev')

        window_min = args.window / 2

        if age < youngest[1] and ev_total > window_min:

            youngest = (sid, age)

            #if args.verbose:

            #    print("window: {} range: {}".format(ev_total, window_min))

    # is the youngest slab class too young?

    if youngest[0] != -1 and oldest[0] != -1:

        if args.verbose:

            print("old:   [class: {}] [age: {:.2f}]\nyoung: [class: {}] [age: {:.2f}]".format(

                int(oldest[0]), oldest[1], int(youngest[0]), youngest[1]))

        if youngest[1] < oldest[1] * args.ratio and w[youngest[0]].get('ev'):

            decision = (oldest[0], youngest[0])

    if (len(history['w']) >= args.window):

        return decision

    return (-1, -1)

def run_move(s, decision):

    s.write("slabs reassign " + str(decision[0]) + " " + str(decision[1]) + "\r\n")

    line = s.readline().rstrip()

    if args.verbose:

        print("move result:", line)

def diff_stats(before, after):

    """ fills out "diffs" as deltas between before/after,

    and "totals" as the sum of all slab classes.

    "_d" postfix to keys means the delta between before/after.

    non-postfix keys are total as of 'after's reading.

    """

    diffs = {}

    totals = {}

    for slabid in after.keys():

        sb = before.get(slabid)

        sa = after.get(slabid)

        if not (sb and sa):

            continue

        slab = sa.copy()

        for k in sa.keys():

            if k not in sb:

                continue

            if k not in totals:

                totals[k] = 0

                totals[k + '_d'] = 0

            if k + '_d' not in slab:

                slab[k + '_d'] = 0

            if re.search(r"^\d+$", sa[k]):

                totals[k] += int(sa[k])

                slab[k] = int(sa[k])

                slab[k + '_d'] = int(sa[k]) - int(sb[k])

                totals[k + '_d'] += int(sa[k]) - int(sb[k])

        slab['slab'] = slabid

        diffs[slabid] = slab

    return (diffs, totals)

def read_stats(s):

    slabs = {}

    for statcmd in ['items', 'slabs']:

        #print("stat cmd: " + statcmd)

        # FIXME: Formatting

        s.write("stats " + statcmd + "\r\n")

        while True:

            line = s.readline().rstrip()

            if line.startswith("END"):

                break

            m = re.match(r"^STAT (?:items:)?(\d+):(\S+) (\S+)", line)

            if m:

                (slab, var, val) = m.groups()

                if slab not in slabs:

                    slabs[slab] = {}

                slabs[slab][var] = val

            #print("line: " + line)

    return slabs

def pct(num, divisor):

    if not divisor:

        return 0

    return (num / divisor)

def show_detail(diffs, totals):

    """ just a pretty printer for some extra data """

    print("\n  {:2s}: {:8s} (pct  ) {:10s} (pct    ) {:6s} (pct)   {:6s}".format('sb',

                'evicted', 'items', 'pages', 'age'))

    for sid, slab in diffs.items():

        if 'evicted_d' not in slab:

            continue

        print("  {:2d}: {:8d} ({:.2f}%) {:10d} ({:.4f}%) {:6d} ({:.2f}%) {:6d}".format(

              int(sid), slab['evicted_d'], pct(slab['evicted_d'], totals['evicted_d']),

              slab['number'], pct(slab['number'], totals['number']),

              slab['total_pages'], pct(slab['total_pages'],

              totals['total_pages']),

              slab['age']))

stats_pre = {}

history = { 'w': [{}] }

while True:

    try:

        with socket.create_connection((host, port), 5) as c:

            s = c.makefile(mode="rw", buffering=1)

            s.write("slabs automove 0\r\n")

            print(s.readline().rstrip())

            while True:

                stats_post = read_stats(s)

                (diffs, totals) = diff_stats(stats_pre, stats_post)

                if args.verbose:

                    show_detail(diffs, totals)

                decision = determine_move(history, diffs, totals)

                if decision[0] != -1 and decision[1] != -1:

                    print("moving page from, to:", decision)

                    if args.automove:

                        run_move(s, decision)

                # Minimize sleeping if we just moved a page to global pool.

                # Improves responsiveness during flushes/quick changes.

                if decision[1] == 0:

                    sleep(0.05)

                else:

                    sleep(args.sleep)

                stats_pre = stats_post

    except:

        err = sys.exc_info()

        print("disconnected:", err[0], err[1])

        traceback.print_exc()

        stats_pre = {}

        history = { 'w': [{}] }

        sleep(args.sleep)