Agile software delivery and schema changes - how do you do it

I work for realestate.com.au and we're an agile delivery shop. We're trying to catch up to some of the best of the best web-shops like Etsy and so on through continuous delivery. Millions of deploys a day!

The big kicker with continuous delivery is around schema changes. I'm curious to know how everyone is performing MySQL (InnoDB) schema changes in a agile continuous delivery shop. So please comment and share your thoughts.

How do we do ours? First off we don't have a good story yet about schema changes though I think we're ahead of the pack

• Limit schema changes to column additions / index changes / new tables
• Perform our schema changes online using Master Master Active Standby replication (using hardware load balancer out the front of our databases - Citrix Netscaler)
• Statement based replication 
• Application fault tolerance (to a degree) - so if a connection is terminated without a 'commit', the application reconnects and retires 
• Tooling around the tedious schema change process - throw the SQL at the tool and have it do the orchestration and coordination aspect ensuring a successful online schema change (and have it call out to nagios for anything suspicious)  

I'm interested to know how others in the community are tackling this problem so please comment.



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