TableGenerators and Sequencing

So I learned today that your persistence.xml may have both a <jta-data-source> and a <non-jta-data-source> specified alongside each other. I’m not sure why I thought these were mutually exclusive but I figured someone else probably had this misunderstanding as well.

(I also was reminded of the fact that JDBC does not support nested transactions in a slightly related tangent.)

I also learned that some JPA providers can take advantage of a double listing: your run-of-the-mill JTA environment (such as an EJB server) will use the <jta-data-source> by default, but the other one might be used by your JPA provider. The JPA specification doesn’t really say anything about this; section 8.2.1.5 is about as close as it gets:

8.2.1.5  jta-data-source, non-jta-data-source
In Java EE environments, the jta-data-source and non-jta-data-source elements are used to specify the global JNDI name of the JTA and/or non-JTA data source to be used by the persistence provider. If neither is specified, the deployer must specify a JTA data source at deployment or a JTA data source must be provided by the container, and a JTA EntityManagerFactory will be created to correspond to it.

These elements name the data source in the local environment; the format of these names and the ability to specify the names are product specific.

In Java SE environments, these elements may be used or the data source information may be specified by other means—depending upon the requirements of the provider.

Specifically, EclipseLink can use your <non-jta-data-source> element if you instruct it—for example—to use a separate connection for @TableGenerator-based identity generation. Otherwise, your sequence table operations will be only as granular as the (potentially long, hairy) transactions that wrap them.

Obviously, your <jta-data-source> and <non-jta-data-source> had better be pointing at the same data source in this case.

File this under “Huh”.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s