Oracle Database 11 g - Online Public Access Catalog

358 CHAPTER 8 ■ ORACLE STREAMSSupport for XMLType Values Stored As CLOBsEffective as of Oracle Database 11g, Oracle Streams extends support for XMLTypes stored asCLOBs. There is one little caveat worth mentioning, though. Old values for the XMLTypesstored as CLOBs are not logged. For conflict detection and resolution, you will need a TIMESTAMPcolumn to be added to your table.Support for Transparent Data EncryptionOracle Database 11g Streams starts support for data encrypted with transparent data encryption.Oracle supports both column- and tablespace-level encryption. (Tablespace encryptionis another Oracle Database 11g new feature that eliminates some of the complications of encrypteddata relative to performance and referential integrity and is discussed more in Chapter 5.)Whether the data is encrypted via the column level or tablespace level, Streams componentshandle the column data in the same way.By default, Oracle Streams handles the capture and apply processes similarly. If the sourcecolumn or tablespace was encrypted with TDE, the Streams apply process will keep intact thelevel of encryption set at the target. The PRESERVE_ENCRYPTION apply parameter can change acolumn from TDE to non-TDE as it applies the messages on the target database. For example,the source database can enforce encryption with TDE, but if the target system does not havelicensing for the Advanced Security Option, the column data can be decrypted before it iswritten to disk. By specifying PRESERVE_ENCRYPTION to N on the target apply process, datawill be decrypted; on the other hand, if the target column is not TDE enabled and PRESERVE_ENCRYPTION is set to Y, you will receive an error. The row LCRs will also be moved to the errorqueue. You can set the preserve encryption using the set_parameter procedure:SQL> begin2 dbms_apply_adm.set_parameter (3 apply_name => 'APPLY_STREAM',4 parameter => 'preserve_encryption',5 value => 'n');6* end;SQL> /PL/SQL procedure successfully completed.Intrinsically, Streams also supports TDE capture for downstream capture processes if thewallet is shared with the source database. The wallet file can be shared via the Network FileSystem (NFS) mount or can be copied manually using the traditional secure file transfer protocolssuch as sftp or scp.