Synchronizing databases through BPEL services by Lykle Thijssen

Introduction

This blog post is about how to synchronize two databases through BPEL, focusing on transaction, rollback and fault handling.

During a project, I’ve encountered a situation where we wanted to migrate from an old database to a new one. However, in order to gradually move external systems from the old to the new database, it was required that both databases would be kept in sync for a limited amount of time. Apart from the obvious database tools, for example Oracle Golden Gate, this can be done through the service layer as well and that’s what this article is about. I will explain how I have done it with a strong focus on fault handling, since that’s the most complicated part of the deal. In this case, since keeping things in sync is what we’re aiming for, a rollback needs to be performed on one database when the other fails to process the update.

One of the requirements is that it should be easy to throw the synchronization code away, as it has no place in our future plans. Another requirement is that the service layer should return faults in a decent manner.

Preparation

In order to enable out-of-the-box rollback functionality, make sure that the data sources connecting to both databases are XA enabled. As there is plenty of information about this subject, I will not get into detail about it in this blog.

Now we will be developing two services:

• SalesOrderBusinessService: a BPEL process that receives messages from a BPM process and forwards them to our integration service
• UpdateSalesOrderIntegrationService: a BPEL process that receives messages from SalesOrderBusinessService and updates two databases through adapters

We need to make sure that both services have a fault specified in their wsdl operation in order to return the recoverable fault. Read the complete article here.

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