B Oracle XML DB Restrictions

This appendix describes the restrictions associated with Oracle XML DB.

Thin JDBC Driver Not Supported by Some XMLType Functions – Methods extract(), transform(), and existsNode() work with the thick JDBC driver only. Not all oracle.xdb.XMLType functions are supported by the thin JDBC driver. If you do not use oracle.xdb.XMLType classes and the OCI driver, you could lose performance benefits.
NCHAR, NVARCHAR, and NCLOB Not Supported – Oracle XML DB does not support the use of SQL data types NCHAR, NVARCHAR, and NCLOB for any of the following:
- Mapping XML elements or attributes to these data types using the SQLType annotation in an XML schema
- Generating XML data from these data types using SQL functions XMLElement, XMLAttributes, and XMLForest
- Within SQL functions XMLQUery and XMLTable, using SQL function ora:view on tables that contain columns with these data types
To handle, store, or generate XML data that contains multibyte characters, Oracle strongly recommends that you use AL32UTF8 as the database character set.
XML Identifier Length Limit – Oracle XML DB supports only XML identifiers that are 4000 characters long, or shorter.
Repository File Size Limit – The maximum size of a file in Oracle XML DB Repository is 4 gigabytes. This implies the following limits for different kinds of file data:
- 4 gigabytes for any LOB, which means 2 gigacharacters for a CLOB stored in the database character set AL32UTF8.
- 4 gigabytes for binary XML encoded data, which can mean from 20 to 40 gigabytes of external XML data before encoding.
- Indeterminate for XML data stored object-relationally.