I actually discussed innodb_thread_concurrency with a MySQL Expert at the Percona Live NYC conference back in May 2011.

I learned something surprising: In spite of the documentation, it is best to leave innodb_thread_concurrency at 0 (infinite concurrency). That way, InnoDB decides the best number of innodb_concurrency_tickets to open for a given MySQL instance setup.

Once you set innodb_thread_concurrency to 0, you can set innodb_read_io_threads and innodb_write_io_threads (both since MySQL 5.1.38) to the maximum value of 64. This should engage more cores.

In this instance, you actually have two choices

CHOICE #1 : Percona XtraDB Cluster

I am currently evaluating it and I think it is brilliantly designed for MultiMaster writes. It can use mysqldump (default), rsync, and xtrabackup (preferred) for initializing new Cluster node. You have total freedom and power. This may be the greatest cliche of all time but WITH GREAT POWER, THEIR MUST ALSO ALWAYS BE GREAT RESPONSIBILITY (19:16 - 19:25 of the Video).

You ultimately become responsible for

• sizing memory requirements and disk configuration for InnoDB
• remembering that DDL/DML on MyISAM is not replicated in the Galera Write Set Replicator Libraries. Since GRANT commands is storage-engine neutral, MyISAM table in the mysql schema is handled with no problem. Any DML against mysql.user is not replicated.
• adding provisioning new Cluster Nodes for Reads/Writes

CHOICE #2 : Amazon RDS

Amazon RDS makes MySQL Database Cloud Services a snap. You must spend some time deploying Servers with one of 7 server models. By default, all InnoDB log files are 128M. Here are the only options that are unique to each Server Model:

MODEL      max_connections innodb_buffer_pool_size
---------  --------------- -----------------------
t1.micro   34                326107136 (  311M)
m1-small   125              1179648000 ( 1125M,  1.097G)
m1-large   623              5882511360 ( 5610M,  5.479G)
m1-xlarge  1263            11922309120 (11370M, 11.103G)
m2-xlarge  1441            13605273600 (12975M, 12.671G)
m2-2xlarge 2900            27367833600 (26100M, 25.488G)
m2-4xlarge 5816            54892953600 (52350M, 51.123G)

You are not given SUPER privilege and there is no direct access to my.cnf. In light of this, in order to change my.cnf options for startup, you must first create a MySQL-based DB Parameter Option List and use the RDS CLI (Command Line Interface) to change the desired Options. Then, you must do this to import the new options:

• Create a Custom DB Parameter Group (call it MySettings)
• Download RDS CLI and setup a config file with your AWS Credentials
• Execute the following : ./rds-modify-db-parameter-group MySettings --parameters "name=whateveroption,value=whatevervalue,method=immediate"
• Modify using DB Parameter Option List MySettings
• Restart the MySQL RDS Instance

As for scaling out to data centers, you have the option to create read replicas. Since the default storage engine is InnoDB, making a read replica becomes seamless because data can be sync'd to Slaves without interrupting the Master.

Higher Server Models means you can have more Memory, more IOPs. Don't forget the cliche I mentioned because when it comes to Amazon RDS, with GREAT POWER COMES GREAT MONEY.