15.  Oracle

15.1. Using Query Hints with Oracle
15.2. Known issues with Oracle

Example 2.15.  Example properties for Oracle

openjpa.ConnectionDriverName: oracle.jdbc.driver.OracleDriver
openjpa.ConnectionURL: jdbc:oracle:thin:@SERVER_NAME:1521:DB_NAME

15.1.  Using Query Hints with Oracle

Oracle has support for "query hints", which are formatted comments embedded in SQL that provide some hint for how the query should be executed. These hints are usually designed to provide suggestions to the Oracle query optimizer for how to efficiently perform a certainly query, and aren't typically needed for any but the most intensive queries.

Example 2.16.  Using Oracle Hints

Query query = em.createQuery(...);
query.setHint("openjpa.hint.OracleSelectHint", "/*+ first_rows(100) */");
List results = query.getResultList();

15.2.  Known issues with Oracle

  • The Oracle JDBC driver has significant differences between different versions. It is important to use the officially supported version of the driver (, which is backward compatible with previous versions of the Oracle server. It can be downloaded from http://www.oracle.com/technology/software/tech/java/sqlj_jdbc/htdocs/jdbc101040.html.

  • For VARCHAR fields, null and a blank string are equivalent. This means that an object that stores a null string field will have it get read back as a blank string.

  • Oracle corp's JDBC driver for Oracle has only limited support for batch updates. The result for OpenJPA is that in some cases, the exact object that failed an optimistic lock check cannot be determined, and OpenJPA will throw an OptimisticVerificationException with more failed objects than actually failed.

  • Oracle cannot store numbers with more than 38 digits in numeric columns.

  • Floats and doubles may lose precision when stored.

  • CLOB columns cannot be used in queries.