概要信息：

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Tim Yang!
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– ±ä

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• Content Manager System!
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• ž, LAMP!
– MySQL master/slave"
– Memcached"
– PHP"
– CDN"
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• x<I

– Real-time"
– ,°,Í

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– Push(Š)"
– Pull(ƒ)"
Push 
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– Inbox: Ž4¾x<

– Outbox: i?àx<

• ?à[4›Ìinbox(ü)!
• ¥ÂÁˆêÿInbox(ò)!
Push(Figure) 
User A 
UpdateAction 
Inbox 
(Append to 1s  
home timeline) 
Inbox 
(Append to 2s  
home timeline) 
Inbox 
(Append to 3s  
home timeline) 
Followers of User A 
= 1, 2, 3 
Push 
•  ¶]¸Ê;Ċõ

• Ô¶0?ý

Pull 
• ?à[4Ûhoutbox(ò)!
• ¥Â›,°bíInbox(ü)!
Pull 
User I 
Get home_timeline 
Outbox 
(statuses sent by A) 
Outbox 
(Statuses sent by B) 
Outbox 
(Statuses sent by C) 
User Is  
Following List 
= A, B, C 
Pull 
•  ¶ÜÎ[)

• Ô¶çËýV

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• 100,000?!
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• Latency!
• DB read timeout!
• 5Ç
timeout (503 error)!
• å/“§

u«éç

• E«Éw

• c´|[+´|Ā2(Message 
Queue)!
• òýϾ?à

MQ products 
• Kestrel by twitter"
• RabbitMQ, an Erlang Queue 
Server"
• Memcacheq!
– O’²x<ćÀVã©#¼

Memcacheq 
• RBerkeley db, Æ\BĆ

• Memcached protocol, a¾
client library!
• _–¿‰(stats queue)!
• A›2Hget/set!
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1. #¼UMemcacheq®

2. GetŒ": ñ뛜9J


3. SetŒ": ßõ„	



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• Offline work!
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The value of the tweet 
decreases 
exponentially with 
time!
    "
John Kalucki, Twitter"
http://t.sina.com.cn/pub/star#a_ty 
å/zï

Cachey:

Ram is the new the disk!
• Local Cache!
• Memcached!
• Database buffer/cache!
• LAMPcache=Bõe

• Cachey:F’¾ÿĉ

_ýÿĉ

• TBÏ

• zï=Ó

– QuickLZ"
– LZO"
– ¼gzip"
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• ;¶ă, SIGSEGV!
• Y!pb

– 1. Consistent hash"
– 2. Read-through cache"
Consistent hash 
• >¹

•  ¶

– ąÝšd

Read-through cache 
Read-through and Write-
through 
• Products or projects!
– MySQL memcached UDF"
– Cache money for Ruby on Rails"
• Or wrap a proxy for the db 
driver, in any language!
Evictionsÿĉ

• Evections: cache‘‡áð

• {Ú¾K¨

• Latency»¾µX	

Y!ø*evictions 
• ã1cache_ý

• c¬‘‡
•‘‡0t

• #¼ĂŸZÈ"key!
Multigetÿĉ

When memcached servers are 
CPU bound, adding more 
memcached servers doesn't 
help serve more requests.!
!
- Jeff Rothschild, Vice President of 
Technology at Facebook"
Cache†~multiget 
hole 
Memcached
(Max RPS: A)
Memcached
(Max RPS C)
Memcached
(Max RPS: B)
Multiget (keys…)
M
ul
tig
et
M
ul
tig
et
M
ul
tig
et
Application
Max RPS of application < (A and B and C) 
M
ul
tig
et
å/“¯

• Memcached replication!
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• Master-slave!
• Master-master"
• 2PC/3PC!
• Paxos!
• http://timyang.net/data/multi-
idc-design/ !
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• MySQL master/slave!
• Dynamo/Cassandra!
• PNUTS!
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