Oracle LOB data can exist in several formats in Oracle. The LOB datatypes in Oracle are:
Character:
LONG
CLOB
NCLOB
Binary:
LONG RAW
BLOB
BFILE
BFILE points to file contents stored outside of the Oracle database.
For those types stored in the database (all types except BFILE), Oracle records the content of the LOB in the redo files. The Mirror Replication Agent reads the LOB data from the redo file and submits the data for replication.
Because BFILE type data is stored outside of the database, the BFILE contents are not recorded in the redo file. To replicate the content of a BFILE, the Mirror Replication Agent connects to the primary Oracle database and issues a query to select the data from the BFILE. Selecting the BFILE data separate from other data in the redo log can provide a temporary out-of-sync condition if the BFILE contents are changed multiple times. As described in the Mirror Activator Administration Guide, querying LOB data from the database “outside” the transaction log’s contents allows only the last change to that BFILE to be replicated. Values from earlier transactions might not be sent to the standby site. See “Enabling and disabling replication for LOB columns” in the Mirror Activator Administration Guide for additional information.
Since the Mirror Replication Agent must query the primary
database to obtain BFILE data, replication of BFILE data will fail
to be replicated if the Primary database is unavailable.
