PyCon Ireland Talk 2011

1. ●
scaling case. From 4 users to 90k+
●
●
Jaime Buelta
●
Soft. Developer at
●

2. The Game

3. Get image from game

4. 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/UtopiaKigdomsGame
http://www.kongregate.com/games/JoltOnline/utopia-kingdoms

5. Technology stack

6. Technology Stack - Backend
Python
Cherrypy framework
Amazon SimpleDB
Linux in Amazon EC2

7. Stack of technologies - Frontend
HTML
( generated by Genshi templates)
jQuery

8. Stack of technologies - Frontend
HTML
( generated by Genshi templates)
jQuery

9. 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

10. Do not guess
Measure

11. Measurement tools
● OS tools
● Task manager (top)
●
IO Monitor (iostat)
● Monitoring tools (Munin, Nagios)
● Logs
●
Needs to find a good compromise detailed/relevance
● Profiling

12. 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

13. 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

14. 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

15. Example of RunSnakeRun
RAZR

16. Example of gprof2dot

17. The power of cache

18. 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

19. Use memcached
(and share the cache between your servers)

20. 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

21. 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

22. Caching is not just memcached
●
More options available:
●
Get on memory on start
●
File cache
●
Cache client side

23. 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

24. More problems

25. 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

26. 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

27. 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

28. 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.

29. DataBase Issues

30. 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

31. 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

32. Problems with SimpleDB
●
Bad tool support
●
Slow and high variability (especially on SQL
queries)
●
Sometime, the queries just timeout and had to be
repeated.

33. Migrate to MongoDB

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

35. 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

36. 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

37. 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']

38. 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')

39. Some features
●
Dirty fields
●
No type checks
●
Query logs
●
10x faster than SimpleDB!!!

40. 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)

41. Scalability vs Efciency

42. Scalable vs Efcient
Scalable Efficient
●
Can support more ●
Can support more
users adding more users with the same
elements elements
Work on both to achieve your goals

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

44. Thank you for your interest!
Questions?
jaime.buelta@gmail.com
http://WrongSideOfMemphis.wordpress.com
http://www.joltonline.com