Scaling Website Performance:
Caching Session and Profile Data with Memcached
Presented by:
Joaquín Ruiz – EVP Products
Perry Krug – Systems Engineer
14 April 2009

About Gear6
• First and leading provider of scalable Memcached solutions
• Enabling high-growth web sites to deliver and scale dynamic
high growth
applications and content
• Memcached contributor on Github and Google Code
• Customers are leaders in media, social networking and content
aggregation
• Privately held; Headquartered in Mountain View, California
2 : Copyright 2009 Gear6 Inc.

The Web Has Changed
• It’s Dynamic, It’s Mobile, It’s High Speed
» Consumer internet traffic surpassed business traffic in 2008
» Dynamic (Social Aggregation Media) sites/services are the driving web growth
(Social, Aggregation,
So…
• A distributed caching tier has become necessary and ubiquitous
» Approximately 70% of websites are Linux-based (typically LAMP/Java) and are not
scalable without a distributed caching tier
Because…
• Without a distributed caching tier you have no good options
SCALE VERTICALLY: $$$ It’s very expensive to do this $$$
»
ADD LARGE AMOUNTS OF WEB, APP AND DB SERVERS: $$$ OPEX $$$
»
MOVE TO A DIFFENT STACK: “No way!
No way!”
»
GET CRUSHED/SLOW RESPONSE TIMES: “It’s gone from bad to worse”
»
“Digital Consumer – Undermonetized social networks / video / VoIP driving powerful usage
growth
growth” – Morgan Stanley Tech Research, 5 Nov 2008, Web 2.0 Summit, San Francisco
3 : Copyright 2009 Gear6 Inc.

Web Architecture with No Cache
Web / Application Servers
MySQL
Databases
Ad Load
Add Load
dd
d
Web / Application Servers
MySQL
Databases
Every request must hit the database servers and/or
E t t th d t b d/
re-
re-execute on application servers
4 : Copyright 2009 Gear6 Inc.

Memcached to the Rescue
• Memcached: a distributed memory object caching system intended
for use in speeding up dynamic web applications by alleviating
database load
• Memcached is an open source project that developed around the
need for dynamic web sites to have a distributed caching tier
» Technology: Memcached is a generic two stage hashing system (clients and
servers). Clients are written for specific application languages. Server is
written in C
» U cases: HTML MySQL, Session/profile caching
Use HTML, M SQL S i/ fil hi
• Memcached is de facto solution
» 85% of top 20 sites use memcached; 50%+ of top 5k sites uses Memcached
» Memcached has client libraries in all major languages
» Memcached has application level plug-ins for apps like WordPress and
Drupal
5 : Copyright 2009 Gear6 Inc.

Why should I use Memcache?
• Enables scale-out of dynamic websites
• Faster page loads
pg
• Allows for efficient use of your database
• Can utilize existing network infrastructure
• Very flexible – architect for your workload & resources
6 : Copyright 2009 Gear6 Inc.

Web Architecture with Memcached
Web / Application Servers
Without Memcached
MySQL
Databases
Web / Application Servers
With Memcached
Perfect for
dynamic website
Memcached
that generate a
Memcache Server(s)
e cac ed
Memcached
high load on their
hi h l d th i
MySQL
Memcached database
Databases
7 : Copyright 2009 Gear6 Inc.

Challenges of Memcached
Challenges:
» Many web implementations require lots of
memory and lots of servers for memcache:
• Ad i i t ti
Administration, power, cooling and
li d
rackspace challenge
» No built-in failover or replication
» Instances managed individually
• Lack of consolidated management and
aggregated statistic gathering
• Can be challenging to troubleshoot client,
service, instance and key relationships
Source: “MySQL and memcached” May 2008 seminar
8 : Copyright 2009 Gear6 Inc.

What is a Session?
• Al
Almost always l
tl larger th
than 250 b t
bytes, and almost
dl t
always smaller than 5 kilobytes
• Read from datastore for every logged in user for
every dynamic page load
• Written to the datastore for every dynamic page
load
• Eventually reaped from the database after N
minutes of inactivity
Credits: “Cache your sessions. Don't piss off your users” by Dormando
9 : Copyright 2009 Gear6 Inc.

Example: Scaling the User Profile
• Too many users creates a load on the database
• Replicating the database will help this
p g p
» Will quickly experience DB replication lag
Source: “”Scaling and Tuning MySQL.com” Jan 2009
10 : Copyright 2009 Gear6 Inc.

Where do you keep your Sessions?
• Bad: Local sessions (on disk or in memory)
» Can’t move users
Can t
» Can’t avoid hotspots
» Not fault tolerant
• Good: Centralized sessions (in a central
database or in-memory)
in memor )
» No porting around of session data
» No need for sticky sessions
» No hot spots
Credits: “Scalable Web Architectures” by Cal Henderson
11 : Copyright 2009 Gear6 Inc.

Caching Sessions with Memcached
• Common Wisdom: You Don’t
» Users will get logged out if anything goes wrong with
memcached
» Evictions means that people are logged out of your site
» If you upgrade memcached, OS, hardware etc., everyone will
be logged off
» Addi /
Adding/removing memcached servers ki k people off site
i hd kicks l ff it
• BUT the benefit of caching sessions is HUGE
» It is VERY FAST - Zero reads or writes to the database
… so people do!
Credits: “Cache your sessions. Don't piss off your users” by Dormando
12 : Copyright 2009 Gear6 Inc.

Session Caching Options
Approach 1:
» Memcached / MySQL hybrid ! Run batch/cron jobs to store session data in
both database and memcached
» Good for smaller sites or sites where it doesn’t matter as much if session
data is lost
(Gear6 Approach):
Approach 2
» Store session in memcached space only
» Provide sufficient memory space to eliminate evictions
• Leverage flash density to reduce space and costs
• Use DRAM to provide low latency
» Use server-based replication to eliminate memcached misses
b d l l hd
13 : Copyright 2009 Gear6 Inc.

Gear6: Session Caching Customer Case
Production Customer Stats:
Alexa rank: top 150 worldwide
»
10’s of millions of page views per day
»
28 million unique users per month in 2008
»
Previously used memcached v 1.2.6 to cache sessions
»
About 120GB of memcache data used
»
Customer challenges:
g
» Need to provide very fast access to use profile information in order
to present user with appropriate content (based on user ratings)
» Customer: rack space limited and cost sensitive
» Need to increase administrative efficiency for memcached tier
» Memcached reload can take several hours if failure occurs during
which DB load is very high and service latency increased
14 : Copyright 2009 Gear6 Inc.

Gear6: Session Caching Customer Case
• Without Gear6:
Zero High Availability / Redundancy
Slower user experience
»
4 U rack space
»
~800W power consumption
800W
»
Zero configuration management
»
Minimal statistics (Cacti)
»
Cost per Gig = $100 for hardware only
»
Double everything for redundancy
32GB 32GB 32GB 32GB
15 : Copyright 2009 Gear6 Inc.

Gear6: Session Caching Customer Case
• With Gear6:
Fully redundant / cache data protection
y p
» 2 U rack space
» ~400W power consumption
» Single point for management
gp g
» Enhanced stream analysis and statistics
» Cost per Gig = $70 for entire solution
Savings & benefits of Gear6 solution vs. without Gear6:
Over $8k/year in power savings
»
Immediately deployable with no code changes
»
1/4th the rack space
»
Customers immediately presented with high-affinity content based
»
on profile and rating history
p g y
» Less expensive to deploy with Gear6 than without!
16 : Copyright 2009 Gear6 Inc.

Gear6 Web Cache Specifications
Gear6 Web Cache Software Gear6 Web Cache Module
• High memory density &
advance memory allocation
» Best-in-class hybrid RAM-Flash
Best in class RAM Flash
configurations
» Advanced memory management
» Most efficient object eviction implementation
Gear6 software delivered on best-of-breed,
» High bandwidth support industry standard servers, DRAM and Flash
• High availability
Module specs:
» Rich cluster functionality
•1 U rack profile with four flash drive bays
» Failover configurations
•Minimum of two modules per appliance
» Cache replication options
•Two power supplies per module
• Advanced management •Four bonded GE ports per module
» Hot key and client analysis •Two Quad Core processors
» Service-wide diagnostics •Up to 300GB per rack unit
» Aggregated physical and logical views
17 : Copyright 2009 Gear6 Inc.

Resources
• www.gear6.com
• Twitter
» twitter.com/memcached
• Github
» http://github.com/zyounker/brutis/tree/master
p //g /y / / /
» http://github.com/rama/statsproxy/tree/master
• Google code
» http://code.google.com/p/brutis/wiki/Readme
» http://code.google.com/p/statsproxy/
18 : Copyright 2009 Gear6 Inc.

April 14, 2009 Webinar Poll Results
If you do use memcached, do you use it for:
None of the above 0%
All of the above 8%
Session and profile caching 0%
Caching HTML web pages 42%
MySQL or other data caching 67%
What client are you using for memcached?
Other 44%
Perl 0%
Java Based 11%
PHP 44%
19 : Copyright 2009 Gear6 Inc.

Questions?
Thank you for attending
“Scaling Website Performance: Caching Session and
Profile D
P fil Data with Memcached”
ihM h d”
presented by Gear6
Joaquin Ruiz
Gear6
salesinfo@gear6.com
+1 650 587 7116
20 : Copyright 2009 Gear6 Inc.