How Memcached Helps Web Sites Handle Rapid Growth

Why Memcached?

Presented by:
Bill Takacs – Director, Product Management

September 2009

Agenda

• Ri of th dynamic web
Rise f the d i b

• Memcached

• The web architecture

• The evolution of a dynamic site and Memcached

• Gear6 solution

2 : Copyright 2009 Gear6 Inc.

The Web: What’s Changed?

• Population

• Traffic

• Content and applications


Web Growth: Population

Forrester: 2 2 billion people online globally by 2013
2.2


Web Growth: Traffic

Cisco: “Annual global IP traffic
Annual
will exceed two-thirds of a zettabyte
(
(667 exabytes) in four y
y ) years”
[by 2013]
Source: Cisco Visual Networking Index,
9 June 2009


Web Growth: Application & Content

Entertainment
Social networking

Static Media Dynamic
Communication
Community-generated content


But growth can be
Growth can be painful
painful
(VERY)

Clients
Internet

CDN
➜ Industry standard servers replaced proprietary SMP
➜ Shift to dynamic content puts strain on origin sites

Interface
➜ Most sites (over 65%) based on LAMP or JAVA

Balancer
Proxy

Load
Net

Web
W
Se
ervers
Apac
che, Nginx,
Lighttpd
L
Web Stack

App
A
Se
ervers
Web Architecture

PHP, Java, Rails, C
C,
)

Per Python
rl,
Database
MySQL,
M
Pos
stgreSQL
(

Stora
Stora
Stora
Stora
age Interfac
age Interfac
age Interfac
age Interfac
ce:
ce:
ce:
ce:
file, block, FC, SCS
SI
SI
SI
SI

Storage

What to do?


Clients
Internet

CDN
Interface

Balancer
Proxy

Load
Net

Webb
Serve
ers Cache Servers
New Caching Architecture

Memcached
Apache, N
Nginx,
Lighttp
pd
Web S k
W b Stack

Appp
Serve
ers
PHP, Java, R
Rails, C,
Perl, Pyt
thon
for Scaling Out

Databa
ase
MySQL,
PostgreS
SQL

Storage Interface:
Storage Interface:
Storage Interface:
Storage Interface:
file, block, FC, SCSI

Storage

Memcached: Pillar of Web 2.0 Architecture

“Everything runs
from memory
in Web 2.0”
Evan Weaver, Twitter, March 2009


The Fix: 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 LiveJournal

• Significantly reduced database load

• Perfect for web sites with high database load

• In use by Facebook, Twitter, myYearbook, others


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
li t
» http://code.google.com/p/memcached/wiki/Clients


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


How Does Memcached Work?

• Client - Server

• H h Function
Hash F ti

• Memcached
» Two stage


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


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


Memcached Clients

• Client hashes key to server list

• Serializes t e object
Se a es the

• Many client libraries
y

• Authentication


What about…..

• Redundancy

• Failover


Consistent Hashing
• Why?

• How does it work?


Commands

• Storage commands:
» Set / Add / Replace /
Append / Prepend / CAS

• Retrieval commands:
» Get / Gets

• Delete / increment /
decrement

• Stats


Memcached UDFs for MySQL

• Suite of functions that
work with Memcached
and MySQL

• Leverage power of
SQL Engine

• Combine tasks
mySQL
• Open source
application
pp


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

Evolution of a Dynamic Site #1
A day in the life of a growing web service

Event: Site has growth in
number of users, sessions, Action: Replicate database
page views and apps, causing (and/or add more app servers)
excessive read load on DB

App Server App Server App Server
App Server App Server App Server App Server App Server App Server

write

read write … write
read read
MySQL MySQL MySQL



Event: Individual caches on the Action: Add memcached server
app/db servers are on servers with underutilized
overwhelmed from chaotic, non- memory resources… results in
deterministic content access even fewer reads to database

memcached memcached memcached

write
it … write
it write
it … write
it
read read read read
MySQL MySQL MySQL MySQL



Event: Memcached needs
more memory resources than Action: Move Memcached
what are available on other servers to dedicated servers
(shared) servers


memcached memcached … memcached

write … write write … write
read read read read
MySQL MySQL MySQL MySQL


What Memcached is NOT:

A persistent data store

A database

Application-specific

A large object cache

Fault-tolerant or highly available


Memcached: Best Practices

• Use with MySQL :-)
y Q )

• Use on 64-bit servers

• Cache “expensive
operations”

• Cache bi-directionally
(
(read/write)
)

• Design to withstand
failures gracefully

• Use consistent hashing


Memcached: Best Practices (cont’d)

• Careful with numbers of connections
» Peak
» Transitions

• Evictions
» Segment Memcached data into separate pools

• O ti i sizing: instances and pools
Optimize i i i t d l

• Instrumentation


Memcache Use Cases

Site Type Repeatable Use

Social networking Profile caching

Content aggregation HTML/page caching

Ad targeting Cookie/profile tracking

Gaming and entertainment Session caching

Location-based services DB query scaling

Relationship
R l ti hi Session caching
S i hi

E-commerce Session and HTML caching


Use Case Example:
Session Management

• 4m+ daily visitors

Web Servers • 15k hits/sec
• 6k updates/sec
Application S
Servers with • Tens of thousands of
Memcached Clients concurrent connections

Memcached Servers
• S
Session tracked and ads
i t k d d d
are placed in accordance
to session
MySQL Servers


Useful Memcached Tools

p
advanced reporter
Track hot keys and clients in Memcached

wireshark
Dissect and analyze Memcached network traffic

brutis
Size and test changes to memcache clusters

statsproxy
View buffered Memcached stats in your browser

cacti
Graph and analyze Memcached statistics


Statsproxy + Cacti Templates

To use the cacti
templates for
memcached with
statsproxy, you
either need to
modify the
templates to use
port 8080 or
change the
statsproxy config to
use port 11211


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


Questions?

Thank you for attending our webinar
“Why Memcached”

Bill Takacs
Gear6
salesinfo@gear6.com
+1 650 587 7118

and please visit our web site at:
www.gear6.com

References
• Danga.com
• Highscalability.com
• Dev.gear6.com
• Groups.google.com/group/memcached
• Code.google.com/p/memcached
• Twitter.com/gearsix
• Cacti.net
• Wireshark.org
• http://dev.mysql.com/doc/mysql-ha-scalability/en/ha-memcached-using-
deployment.html
• http://dev.mysql.com/doc/mysql-ha-scalability/en/ha-memcached-using-
hashtypes.html
• http://jayant7k.blogspot.com/2009/04/memcached-replication.html
• http://www.lexemetech.com/2007/11/consistent-hashing.html
• http://www8.org/w8-papers/2a-
webserver/caching/paper2.htmlhttp://www.last.fm/user/RJ/journal/2007/04/10/rz_l
ibketama_-_a_consistent_hashing_algo_for_memcache_clients
• http://bazaar.launchpad.net/~libmemcached-
http://bazaar launchpad net/~libmemcached
developers/libmemcached/trunk/revision/539

How Memcached Helps Web Sites Handle Rapid Growth

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