Mysql 2007 Tech At Digg V3

Technology at digg.com
Elliott White III - Eli
Tim Ellis - Time

What's all this then?
History of Tech at Digg
Standard Setup
Memcached
Purpose Driven MySQL Server Pools
Sharding
Other MySQL details

History of Tech at Digg
Initially one Linux server with Apache 1.3 and PHP 4.x
MySQL 4.0 and myisam tables & MySQL full-text search
Started with as many open source packages as possible for rapid development.
ImageMagick, Ispell, prototype/scriptaculous, etc
Grew quick. One server became two. myisam become innodb. We moved to 3 servers, Apache 2.x, MySQL master-slave replication, started using memcached, moved to PHP 5.x & hired a dba
And then the pace picked up yet again...

A Standard Setup Many PHP Servers behind a load balancer:

A Standard Setup Many MySQL slaves, talking to a master

A Standard Setup Randomized PHP to MySQL relations

Memcached What is it & Why use it? Why not just pregenerate pages of content?
Performance gains:
Caching certain chunks of data that may be used on many different pages.
From that, still being able to dynamically create the page, but using cached data.

Memcached Server Farm
Issues to be solved:
Allowing for Failover and Redundancy
Removing or ignoring stale data upon machine failure
Stopping perpetuation of database slave lag
Making the actual decisions of what and when to cache
Solution: Write generic code that understands your data.

Purpose Driven MySQL Pools Creating separate slave pools, that are close to identical in order to isolate high database load.

Purpose Driven Pool Example

Sharding Simplest Definition: Breaking up your database into a number of smaller ones.
Pros
Greater performance
Tweakable / Scalable
Cons
Loss of SQL support (JOIN)
Increased PHP load
Complicated programming

Possible Types of Sharding Table-based Range-based Date-based Hashed Partial Sharding

How MySQL Can Do Sharding
Partition tables
Federated tables
MySQL Cluster (NDB)
Which of these technologies does Digg use?
None of them
They weren't ready when we needed them

Digg MySQL Specifics
Mix of MySQL 5.0 versions: 5.0.22, 5.0.27, 5.0.30, 5.0.32
A single MySQL 4.1 supporting Cacti
MySQL installation & patching done via Debian apt
5.0 performs fine for us compared to 4.1
OLTP DBs are InnoDB & OLAP DB is MyISAM
InnoDB backup DB for dumps and slave creation
InnoDB recovery faster after slave hardware dies
MyISAM great for loads and date-versioned DBs

Current DB Challenges
Scaled via “buy more RAM,” can't afford that anymore
Physical I/O common, so rewrite queries
Convincing site architects to change features to more scalable alternatives
MySQL debug binary testing
Schema cruft
Managing monitoring & alerting systems (Cacti)
Master is a single point of failure (not as bad as it sounds)
Why are our disks lying? Use diskTest.pl from: http://faemalia.net/mysqlUtils

Any Questions?
For this presentation and more: http://eliw.com/
Visit http://digg.com/

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Mysql 2007 Tech At Digg V3

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Mysql 2007 Tech At Digg V3 — Presentation Transcript