Large object (LOB) datatypes (such as BLOB, CLOB, IMAGE, and TEXT) provide support for the longest streams of character and binary data in a single column. The size of the LOB datatypes poses unique challenges, both as primary and replicate data.
The LOB datatypes impact the transaction logging function at the primary database.
For Replication Agents, the log resources must be adequate to support retention of the changes in LOB data, only after images of LOB data are logged. The ability of LOB replication depends on the capabilities of the Replication Agent.
When a non-Sybase database is the replicate database, the database gateway used to communicate with the replicate database must be able to emulate the Adaptive Server text pointer processing.
The ECDA Option for ODBC to Microsoft and the Mainframe Connect™ DirectConnect for z/OS Option gateways provide this feature. The ECDA Option for ODBC to DB2 UDB does not provide this feature. ExpressConnect (for Oracle or HANA DB) does not require support for text pointer processing to support LOB replication. ExpressConnect (for Oracle or HANA DB) supports LOB replication but not text pointer processing, which is not required.
Adaptive Server Enterprise uses a text pointer to identify the location of text and image column data. The text pointer is passed to system functions that perform the actual updates to data in these large columns. The same technique is used internally in Replication Server to apply LOB datatypes. Replication Server obtains a text pointer, and data server function calls are made to apply the data to replicate databases.
The ECDA Option for ODBC provides support for LOB replication into Microsoft SQL Server databases.