This document discusses using Memcached to scale MySQL databases. It provides an overview of Memcached, how it works, example architectures using Memcached with MySQL, and customer examples. Memcached is an in-memory key-value store that can cache data and objects to improve performance and reduce database load. It uses consistent hashing to distribute cache data across servers. Common uses include caching dynamic web content and improving page load performance for sites with high database traffic.

1. MySQL Scaling with Memcached
Presented by: Bill Takacs
Director, Product Management
July 9th 2009

2. Agenda
• M SQL overview
MySQL i
• Memcached overview
• What’s Memcached good for – and
how does it help me scale MySQL?
• Example architectures
• Customer examples
2 : Copyright 2009 Gear6 Inc.

3. About MySQL
• 12 years old
• 400+ employees
00 e p oyees
• 750 partners
p
• 60K downloads/day
• Customers across every major operating system,
hardware vendor, geography, industry, and application
h d d h i d t d li ti
type
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4. Cache is King
Browser cache
Web
W b server cache
h
Memcached cache
MySQL database cache – query cache
Disk
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5. Memcached
“A high performance, distributed memory object caching
g p , y j g
system, generic in nature, but intended for use in
speeding up dynamic web applications by alleviating
database load”
Ref: http://www.danga.com/memcached/
• Big hash table
• Created by Danga Interactive for Live Journal
• Significantly reduced database load
• Perfect for web sites with high database load
• In use by Facebook, Twitter, MyYearBook, others
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6. More on Memcached
• Takes advantage of available DRAM
• Open source
Ope sou ce
• Distributed under BSD license
• Server - Current version is 1.2.8
» http://www.danga.com/memcached/download.bml
• M
Many Clients
Cli t
» http://code.google.com/p/memcached/wiki/Clients
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7. Why Memcached with MySQL?
• Scale-out of dynamic web sites
y
• Page loads
• Efficient resource utilization
• Support for dozens
to hundreds of nodes
• Open source
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8. How Does Memcached Work?
• Client - Server
• H h Function
Hash F ti
• Memcached
» Two stage
» Key / value p
y pair
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9. Memcached Server
• Slab allocator
• Libevent based
• Simple Protocol (no xml)
• Server has internal hash table
• Servers are dumb – they don’t know about each other
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10. Memcached Server
• Limits
» Key size = (250 bytes)
» 1MB Limit
» 32bit/64bit (maximum size of process)
• LRU
» Least recently accessed items are cycled out
» One LRU exists per “slab class”
slab class
» LRU “evictions” need not be common
• Threads? Yes
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11. Memcached Clients
• Client hashes key to server list
• Serializes t e object
Se a es the
• Many client libraries
y
• Authentication
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12. What about…..
• Redundancy
• Failover
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13. Consistent Hashing
• Why?
• How does it work?
» Libk t
Libketama
» http://www.last.fm/user/RJ/journal/2007/04/10/rz_libketama_-
_a_consistent_hashing_algo_for_memcache_clients
• Reference:
http://www.lexemetech.com/2007/11/consistent-hashing.html
p g
http://www8.org/w8-papers/2a-
webserver/caching/paper2.htmlhttp://www.last.fm/user/RJ/jo
urnal/2007/04/10/rz_libketama_-
_a_consistent_hashing_algo_for_memcache_clients
a consistent hashing algo for memcache clients
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14. Commands
• Storage commands:
» Set / Add / Replace /
Append / Prepend / CAS
• Retrieval commands:
» Get / Gets
• Delete / increment /
decrement
• Stats
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15. Memcached UDFs for MySQL
• Suite of functions that work
with Memcached and MySQL
• Leverage power of SQL Engine
• Combine tasks
• O
Open source
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16. Putting it all together
Client 1
Client-1 Client 2
Client-2 Client 3
Client-3
C
Server X Server Y Server Z
Key = value
y
Foo = seattle
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17. Some Architectures

18. Memcached and Single MySQL
Read Write
Web Servers
Application Servers
Memcached Clients
Memcached Servers
Cache Update
MySQL
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19. MySQL Replication Scale-Out
Web / Application Servers MySQL
+ +
Memached Clients Memcached Servers
Writes
MySQL
Replication
Reads
Reads
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20. Memcached and MySQL Replication
Read from cache Write Read from slave
Application Severs
+
Memcached Clients
Memcached Servers
Cache Update
MySQL Master
MySQL Slaves
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21. Memcached and MySQL Replication
Read from cache Write Read from slave
Application Severs
+
Memcached Clients
Shard1 Cust_id 0-999 Shard1 Cust_id 1000 -1999
Cache Update Cache Update
MySQL MySQL
Replication Replication
21 : Copyright 2009 Gear6 Inc.

22. About Gear6
• First and leading provider
of Memcached solutions
• Memcached solution including
• High density
• High Availability
• Advanced memory
management
• Enhanced reporting
capabilities
biliti
• Support for multi-tenancy
• Disruption free
software upgrades
• 100% c e t co pat b e
00% client compatible
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23. Credits and References
• Designing and Implementing Scalable Applications with Memcached and MySQL, Monty
Taylor
http://www.mysql.com/why-mysql/white-papers/mysql_wp_memcached.php
• Memcached Study, Brian Acker
http://download.tangent.org/talks/Memcached%20Study.pdf
htt //d l dt t /t lk /M h d%20St d df
• A Bunch of Great Strategies for Using Memcached and MySQL Better Together, Todd Hoff
http://highscalability.com/bunch great strategies using memcached and mysql better together
http://highscalability.com/bunch-great-strategies-using-memcached-and-mysql-better-together
• Memcached Functions for MySQL: Seamless Caching for MySQL, Patrick Galbraith
http://www.scribd.com/doc/15014678/memcached-Functions-for-MySQL-Seemless-Caching-in-
MySQL
• Memcached Protocol
http://code.sixapart.com/svn/memcached/trunk/server/doc/protocol.txt
http://code sixapart com/svn/memcached/trunk/server/doc/protocol txt
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24. Thank You!
For more information
information:
www.gear6.com
www gear6 com
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