● scaling case. From 4 users to 90k+●

● Jaime Buelta● Soft. Developer at

●

The Game

Get image from game

Utopia Kingdoms

● Fantasy strategy game● Build your own Kingdom● Create armies and attack other Kingdoms● Join other Kingdoms in an Alliance● Manage resources● Available in Facebook and Kongregate

http://www.facebook.com/UtopiaKigdomsGamehttp://www.kongregate.com/games/JoltOnline/utopia-kingdoms

Technology stack

Technology Stack - Backend

PythonCherrypy framework

Amazon SimpleDBLinux in Amazon EC2

Stack of technologies - Frontend

HTML( generated by Genshi templates)

jQuery

Stack of technologies - Frontend

HTML( generated by Genshi templates)

jQuery

Some points of interest(will discuss them later)

● Your resources (population, gold, food, etc) grows with time

● You actions (build something, attack a player) typically takes some time

● Players are ranked against the rest● You can add friends and enemies

Do not guess

Measure

Measurement tools

● OS tools● Task manager (top)● IO Monitor (iostat)

● Monitoring tools (Munin, Nagios)

● Logs● Needs to find a good compromise detailed/relevance

● Profiling

You've got to love profiling

● Generate profiles with cProfile module

Profile whole application with

python -m cProfile -o file.prof my_app.py

(not very useful in a web app)

● If you're using a framework, profile only your functions to reduce noise

Profile decorator (example)

def profile_this(func):

import cProfile

prof = cProfile.Profile()

retval = prof.runcall(func)

filename = 'profile-{ts}.prof'.format(time.time())

prof.dumpstats(filename)

return retval

Analyzing profile

● gprof2dot● Using dot, convert to graph

gprof2dot -f pstats file.prof | dot -Tpng -o file.png

● Good for workflows

● RunSnakeRun● Good for cumulative times

Example of RunSnakeRunRAZR

Example of gprof2dot

The power of cache

All static should be out of python

● Use a good web server to serve all static content (Static HTML, CSS, JavaScript code)

● Some options● Apache● Nginx● Cherokee● Amazon S3

Use memcached(and share the cache between your servers)

Example

● Asking for friends/enemies to DB● Costly request in SimpleDB (using SQL statement)

● On each request● Cache the friends on memcache for 1 hour● Invalidate the cache if adding/removing

friends or enemies

Caching caveats

● Cache only after knowing there is a problem● Do not trust in cache for storage● Take a look on size of cached data● Choosing a good cache time can be difcult /

Invalidate cache can be complex● Some data is too dynamic to be cached

Caching is not just memcached

● More options available:● Get on memory on start● File cache● Cache client side

Parse templates just once

● The template rendering modules have options to parse the templates just once

● Be sure to activate it in production● In development, you'll most likely want to

parse them each time

● Same apply to regex, specially complex ones

More problems

Rankings

● Sort players on the DB is slow when you grow the number of players

● Solution:● Independent ranking server (operates just in

memory)● Works using binary trees● Small Django project, communicates using xmlrpc

● Inconvenient:● Data is not persistent, if the rankings server goes

down, needs time to reconstruct the rankings

Database pulling - Resources

● There was a process just taking care of the growth of resources.● It goes element by element, and increasing the

values● It pulls the DB constantly, even when the user has

their values to maximum● Increment the resources of a user just the next

time is accessed (by himself or by others)● No usage of DB when the user is not in use● The request already reads from DB the user

Database pulling - Actions

● Lots of actions are delayed. Recruit a unit, buildings, raids...

● A process check each user if an action has to be done NOW.● Tons of reads just to check “not now”● Great delay in some actions, as they are not

executed in time

Database pulling - Actions

● Implement a queue to execute the actions at the proper time:● Beanstalk (allows deferred extraction)● A process listen to this queue and performs the

action, independently from request servers.● The process can be launched in a diferent

machine.● Multiple process can extract actions faster.

DataBase Issues

Amazon SimpleDB

● Key – Value storage● Capable of SQL queries● Store a dictionary (schemaless, multiple

columns)● All the values are strings● Access through boto module● Pay per use

Problems with SimpleDB

● Lack of control● Can't use local copy

– In development, you must access Amazon servers (slow and costly)

● Can't backup except manually● Can't analyze or change DB (e.g. can't define

indexes)● Can't monitor DB

Problems with SimpleDB

● Bad tool support● Slow and high variability (especially on SQL

queries)● Sometime, the queries just timeout and had to be

repeated.

Migrate to MongoDB

MongoDB

● NoSQL● Schemaless● Fast● Allow complex queries● Retain control (backups, measure queries, etc)● Previous experience using it from ChampMan

Requisites of the migration

● Low-level approach● Objects are basically dictionaries● Be able to save dirty fields (avoid saving

unchanged values)● Log queries to measure performance

MongoSpell● Thin wrap over pymongo● Objects are just dictionary-like elements● Minimal schema● Fast!● Able to log queries● It will probably be released soon as Open

Source

Definition of collections

class Spell(Document):

collection_name = 'spells'

needed_fields = ['name',

'cost',

'duration']

optional_fields = [

'elemental',

]

activate_dirty_fields = True

indexes = ['name__unique', 'cost']

Querying from DB

Spell.get_from_db(name='fireball')

Spell.filter()

Spell.filter(sort='name')

Spell.filter(name__in=['fireball', 'magic missile'])

Spell.filter(elemental__fire__gt=2)

Spell.filter(duration__gt=2,

cost=3, hint='cost')

Spell.filter(name='fireball', only='cost')

Some features

● Dirty fields● No type checks● Query logs● 10x faster than SimpleDB!!!

Query logs

[07:46:06]- 2.6 ms – get_from_db - Reinforcement - Reinforcements.py(31)[07:46:06]- 4.3 ms - get_from_db - Player - Player.py(876)[07:46:10]- 0.1 ms - filter - Membership- AllianceMembership.py(110) [07:46:10]- 1.3 ms - get_from_db - Reinforcement -Reinforcements.py(31)[07:46:10]- 1.4 ms - get_from_db - Notifications - Notifications.py (56)

Scalability vs Efciency

Scalable vs Efcient

Scalable● Can support more

users adding more elements

Efficient● Can support more

users with the same elements

Work on both to achieve your goals

Keep measuring and improving!(and monitor production to be proactive)

Thank you for your interest!

Questions?

jaime.buelta@gmail.comhttp://WrongSideOfMemphis.wordpress.com

http://www.joltonline.com