Example 3.14. Example properties for Oracle
kodo.ConnectionDriverName: oracle.jdbc.driver.OracleDriver kodo.ConnectionURL: jdbc:oracle:thin:@SERVER_NAME:1521:DB_NAME
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 3.15. Using Oracle Hints
JDO:
Query query = pm.newQuery (...);
query.addExtension ("openjpa.hint.OracleSelectHint", "/*+ first_rows(100) */");
List results = (List) query.execute ();
JPA:
Query query = em.createQuery (...);
query.setHint ("openjpa.hint.OracleSelectHint", "/*+ first_rows(100) */");
List results = query.getResultList ();
The Oracle JDBC driver has significant differences between different versions. It is important to use the officially supported version of the driver (10.2.0.1.0), which is backward compatible with previous versions of the Oracle server.
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 Kodo is
that in some cases, the exact object that failed an
optimistic lock check cannot be determined, and Kodo
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.
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