Infrastructure for Highly Concurrent, High Write DB
If you are using MySQL as the main database, you may want to consider using a Star Topology via MySQL Replication.

Now, before you say UGHHH, ROFL and OMG to MySQL Replication, hear me out.

A star topology allows you to write to one DB server (called a Distribution Mster [DM]) and send the SQL commands to several DB servers. How do you setup such a DB infrastructure?

Here is the Description

You have 5 DB servers (server A,B,C,D,E)

Server A


In MySQL Replication setup, it will be the Master
Plays special role as the DM
Master of servers B,C,D,E
All tables use the storage engine BLACKHOLE (/dev/null)
Only stores binary logs
Bare Metal Machine
Benefits


Very fast writes since all tables on the DM use BLACKHOLE
Network Latency is less of a issue since reads are 15-30% of DB Activity
All slaves are updated strictly from the DM



Servers B,C,D,E


Slave of A
Server a base for heavy SELECTs
Server Can Be Virtual or Bare Metal
For all servers whose user tables use the storage engine InnoDB


It can server as a warm standby DB Server
Nonintrusive backups can be run against it

For all servers whose user tables use the storage engine MyISAM


Set up with read-only oprion
Tables can have their row formats redone to accelerrate reads



I have written posts on this before


https://serverfault.com/questions/264374/mysql-in-star-topology/264444#264444
https://stackoverflow.com/questions/5273043/mysql-in-star-topology/5781504#5781504


To keep MySQL Replication in tip top shape


Use MySQL 5.5
Use Semisynchronous Replication
Tune InnoDB to engage more CPUs