Example 2.17. Example properties for Oracle
openjpa.ConnectionDriverName: oracle.jdbc.driver.OracleDriver openjpa.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 certain query, and aren't typically needed for any but the most intensive queries.
Example 2.18. Using Oracle Hints
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 drivers (10.2.0.1.0/11.2.0.x.0), which is backward compatible with previous versions of the Oracle server. It can be downloaded from http://www.oracle.com/technetwork/database/features/jdbc/index-091264.html.
Empty string/char values are stored as NULL.
Oracle corp's JDBC driver for Oracle has only limited support for batch updates.
The result for OpenJPA is that batching of some statements may fail and in some cases,
the exact object that failed an optimistic lock check cannot be determined. OpenJPA will
throw an OptimisticException with more failed objects than actually
failed. This situation may be resolved by disabling statement batching by setting the
batchLimit value to zero or by using a more recent Oracle JDBC Driver (11.2.0.1) with
batch support improvements. Attempting to resolve the issue with a more current driver
is recommended since disabling statement batching can result in a decrease in performance.
Example 2.19. Property to disable statement batching for Oracle
openjpa.jdbc.DBDictionary: oracle(batchLimit=0)
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.
The use of LOBs with persistent attributes of a streaming data type (ex.
java.io.InputStream or java.io.Reader) may
require the same connection to be used over the life of the transaction or
entity manager. If the same connection is not used for persistent operations
a java.io.IOException with message Closed Connection
may result. The OpenJPA property openjpa.ConnectionRetainMode
can be used to control how OpenJPA uses datastore connections. See
Section 8, “
Configuring the Use of JDBC Connections
” for details.
Example 2.20. Property to retain connection over the lifetime of the entity manager
openjpa.ConnectionRetainMode: always
Mapping persistent attributes to XML columns requires
a JDBC 4 compliant driver if XML strings are longer than 4000 bytes, as counted in database.
Otherwise an ORA-01461: can bind a LONG value only for insert into a LONG column
error may result.
If Oracle dictionary property MaxEmbeddedBlobSize or
MaxEmbeddedClobSize is set to some limit (i.e. not -1) and embedded collection
with BLOB/CLOB attribute is used, a
"org.apache.openjpa.persistence.ArgumentException:
"x.y.z.EmbedOwner.embedCollection<element:class x.y.z.EmbedValue>"
is mapped as embedded, but embedded field
"x.y.z.EmbedOwner.embedCollection.x.y.z.EmbedValue.blob" is not embeddable.
Embedded element/key/value types are limited to simple fields and direct relations to other
persistent types" error may result. To overcome this limitation, either use JDBC driver
11.2.0.x.0 (or later version) or set both MaxEmbeddedBlobSize and
MaxEmbeddedClobSize properties to -1.