Presentation in OGDC 2012 organized by VNG Corp.

1. Data Storage Solutions
for SNS game
Dinh Nguyen Anh Dung – P2S – G6 – VNG

2. CONTENT
• SNS games and SQL-based databases
• NoSQL technology and Couchbase
• NoSQL does not come without challenges
• SNS Storage Engine (SSE)

3. SNS games AND SQL-based databases

4. SNS games characteristics
• Huge amount of concurrent requests but
require low response time
• Accounts can be stored separately
– No need for centralized storage
– In most cases, no need to put strict constrains on
data relationship

5. Native limitations of SQL-based DBMS
• Centralized fundamentally
– Vertical scale up issue
• Schema
– High risk (and cost) for updates
• Normalized data
– Unnecessary overhead: join tables, locking, data
constrain check,…

6. Native limitations of SQL-based DBMS
Source : NoSQL - WhitePaper

7. Native limitations of SQL-based DBMS
• SQL processing overhead at both DBMS and
client side.
• Most data accesses end up at hard-disk
– Very challenging to meet low response time
– Internal caching does not help much
• Hard to distributed data across multiple-
servers

8. NoSQL technology and Couchbase

9. NoSQL technology
• Persistent distributed hash-table
• Active set resides on RAM
– Extremely fast response time
• Horizontal scale up
• Raw and direct data access
– set, get, add, inc, dec : no overhead

10. NoSQL technology
Key Value
Jack.Gold 50123
Jack.Exp 4670
Jack.Coin 700
Peter.Gold 7050
Peter.Exp 20005
Peter.Coin 1
Key Value Key Value Key Value
Peter.Gold 7050 Jack.Gold 50123 Peter.Coin 1
Jack.Exp 4670 Jack.Coin 700
Peter.Exp 20005

11. Active set on RAM
CLIENT
ACTIVE SET ON RAM
Lazy write
HDD

12. Couchbase server
• Based on membase technology
• Distributed
• Replica
• Since 1.8, have native client for PHP
• Bucket types
– Couchbase (persistent)
– Memcache (memory only)

13. NoSQL does not come without challenges

14. Our first SNS game with Couchbase

15. Architecture and design issues
• Transition from relational database design to
key-value design
– Account data => keys : how ?
• Only minimum support for
locking, concurrency control
– add : failed if exists - mutex
– cas : read get cas, write failed if cas is out-dated

16. Architecture and design issues
• No transaction support
– Data corruption becomes so easy!
• No high-level data support (e.g. list,queue,…)
• No tools for raw data viewing / editing

17. Pitfalls
• Too much freedom for developers
– Anyone can add / modify any key any time
• Epic key design mindset
– One key for all : bad performance, concurrency
control is a true night mare
• Abuse the power of set
– Never fail ! Developer LOVE it !

18. SSE – SNS Storage Engine

19. Our second SNS game with Couchbase

20. What is SSE ?
• A thin “layer” between developers and the
all-mighty Couchbase
– SSE is simply a PHP library
• Provide better support for locking and
concurrency control
– Basic support for : Begin – update - commit
• Provide high-level data structures
– Collection, queue, stack, integer (gold), inc-only
integer (exp), binary flags (quest)…

21. What is SSE ?
• Minimize the risk of weak concurrency support
– Ability to rollback pending writes
• Schema
– Limit freedom of developers!
– No more nightmare for backup and raw data
view/editing
• Buffers to eliminate repeated read / writes

22. Raw account view / editing tool

23. What is SSE ?

24. What is SSE ?

25. Multi-instance architecture
• Replica is too costly to performance
• One node failed means cluster failed
• Adding nodes requires rebalance
– Only good when having clusters with large
number of nodes (more than 20 nodes)

26. Multi-instance architecture
• One instance for index (user-to-instance
mapping)
– Use APC on logic servers to cache / reduce load
to index instance
• Many instances of data
– Dynamically adjust weight on each instance base
on average load of instance
– Node failure only affects part of the user-base

27. Multi-instance architecture
Game Logic Game Logic Game Logic Game Logic
APC APC APC APC
Index Data Data Data
Instance Instance 1 Instance 2 Instance 3

28. Disavantages
• Lower performance of multi-get
• Not well balance between instances in terms
of accesses

29. How good is SSE for us ?
• No more data loss due to concurrency
• No more data corruption
• No mysterious bugs due to un-intended
writes
• Reduce more than 3 times workload of server
developers