An End in Sight to Upgrade Downtime?

One of the recurring concerns that our customers raise with us is the amount of downtime required when we make a change to the application.

We have spent time and money putting a bunch of high availability technologies in place so it always seems disappointing to have to ask for downtime to do something as simple as an application code change. Somehow this fairly frequent activity has not caught the attention of the folks who think up clever new ways to improve database availability... until now.

In our case the application is a Telecoms inventory solution based on the Amdocs Cramer product using J2EE (WebLogic or Oracle App Server) and an Oracle database. The product is very 'database heavy' in that a large proportion of its code resides in the database as Oracle stored procedures or database resident Java code. The complexity of the dependencies inside the product means that any changes typically require an outage of several hours while the database code is replaced and recompiled.

We have looked at various ways to solve this problem. The main option being to run multiple instances of the application and replicate data changes between them somehow. When upgrade time arrives, one instance can be used to apply the code changes while the other stays online running transactions and the data changes are replicated across before the instance with the updated code takes over as the live instance. We've looked at Oracle streams, Data Guard SQL Apply and GoldenGate as possible solutions. All of them seemed to offer the possibility of doing the job but somehow the complexity and cost always meant that the idea was never followed through to implementation.

There is now another way to achieve the same result - without the need for a separate instance of the application. Oracle 11g release 2 has introduced a feature called 'Edition-Based Redefinition'. The new feature allows multiple versions of the same procedure to exist in the database so that clients can carry on using the old version while the new one is being built. The new versions can also be kept
separate during testing and if necessary even run in parallel for longer periods of time.

Edition-Based Redefinition is probably still some way in the future for us at the moment - I think it will need changes by our product vendor, not least that they need to support Oracle 11g.

Some links containing more detail:-

A 2 part YouTube video with Bryn Llewellyn
Part 1
Part 2

Tom Kyte's very thorough explanation of Edition-Based Redefinition
Part 1
Part 2
Part 3

Bryn Llewellyn's White Paper

The Manual