Versioning with read_uncommitted Isolation Level 

Use

You use this procedure to enable JPA versioning on DataSources that have read_uncommitted isolation level. The JPA specification requires that in order to use versioning, you must use a DataSource with a read_committed isolation level. To resolve the difference between the specification requirement and the DataSource isolation level, you use a version generator. Thus, you can use JPA versioning on DataSources with read_uncommitted level. The version generator has the following behavior:

DataSource Isolation Level	read_committed	read_uncommitted
With Generator Table	The container recognizes the table and uses it. Versioning works fine.	The container recognizes the table and uses it. Versioning works fine.
Without Generator Table	Versioning works fine.	The container recognizes the difference in isolation levels and throws an exception.

The version generator resolves the read_uncommitted versioning problem only. If you use read_uncommitted, other dirty read effects may occur as well. We recommend that you use read_committed isolation level.

Prerequisites

●      You have created your entity.

●      Your entity uses versioning.

Procedure

...

       1.      To use JPA versioning on DataSources with read_uncommitted isolation, you use a version generator. The version generator needs a database table to work with. You can choose an arbitrary name of the version generator table (in the example below, table name is TMP_VERSION_GEN). However, the column names and their corresponding types are fixed (as shown in the table below).

The following table lists the required columns and corresponding types for the version generator table with name TMP_VERSION_GEN:

Column Name	Key	Built-in Type	JDBC Type	Length	Not Null
GEN_KEY	Yes	String	VARCHAR	256	Yes
GEN_VALUE	No	Long	BIGINT		Yes

You should use the details above to define the version generator table using Java Dictionary.

More information: Creating Tables

       2.      For the version generator to work, you must also specify the name of your version generator table as value of the com.sap.engine.services.orpersistence.generator.versiontablename property in the persistence.xml:

 

<persistence-unit name="demos/myDemoApp">

      <description> Persistence Unit</description>   

      <jta-data-source>sapdemo</jta-data-source>

      <properties>

         <property name="com.sap.engine.services.orpersistence.generator.versiontablename" value="TMP_VERSION_GEN"/>

      </properties>

   </persistence-unit>