We have a service in a stateless session bean that must perform the following:
1. Find an EntityBean using a known PK using home.findByPrimaryKey()
2. If this fails with a FinderException then create the EntityBean using home.create()
Our SLSB is defined as having transaction-type of "Bean" and we start a transaction here using SessionContext.getUserTransaction().begin()
Our EntityBean is CMP and the SLSB is deployed to more than 1 node within our cluster.
So the flow is:
SLSB --> begin transaction --> findByPrimaryKey() --> if not found create() --> commit transaction
My question is as follows:
Is it possible that another transaction can fail to find the bean and create it, thus causing our transaction to fail at the create stage due to a PK unique constraint?
How can we prevent this? I've read up about database isolation levels and TRANSACTION_SERIALIZABLE seems to fit the bill but it would appear to be possibly a big performance hit?
Are there any other ways of effectively synchronizing this logic (bearing in mind we run a JBoss cluster)
Has anyone else come across this kind of problem?
Many thanks,
mark
