SQL Replication supports large object (LOB) data types,
including binary LOB (BLOB), character LOB (CLOB), and double-byte
character LOB (DBCLOB).
This topic refers to BLOB, CLOB, and DBCLOB data types as LOB data
The Capture program reads the LOB descriptor in the log records
to determine if any data in the LOB column has changed and thus should
be replicated, but does not copy the LOB data to the change-data (CD)
tables. When a LOB column changes, the Capture program sets an indicator
in the CD table. When the Apply program reads this indicator, the
Apply program then copies the entire LOB column (not just the changed
portions of LOB columns) directly from the source table to the target
table.
Because a LOB column can contain up to two gigabytes of data, you
must ensure that you have sufficient network bandwidth for the Apply
program. Likewise, your target tables must have sufficient disk space
to accommodate LOB data.
Restrictions: - The Apply program always copies the most current version of a
LOB column directly from the source table (not the CD table), even
if that column is more current than other columns in the CD table.
Therefore, if the LOB column in the target row changes, it is possible
that this LOB column could be inconsistent with the rest of the data
in that target row. To reduce this possibility of inconsistent data
in the target row, ensure that the interval between the Apply cycles
is as short as practical for your application.
- You can replicate 15 LOB columns
or fewer per table. If you register a table with more than 15 LOB
columns, the Apply program returns an error message. The Replication
Center returns an error message if you attempt to register more than
15 LOB columns per table.
- You can copy LOB data to replica tables provided that conflict
detection is disabled.
- To copy LOB data between DB2® for OS/390® Version
6 (or later) and DB2 for Linux, UNIX,
and Windows, you need DB2 Connect™ Version 7 or later.
- You cannot refer to LOB data by using nicknames.
- Before-image values for LOB or ROWID columns are not supported.
- Replication is not supported for DB2 Extenders™ for Text, Audio, Video, Image, or other extenders where
additional control files associated with the extender's LOB column
data are maintained outside of the database.
- SQL Replication can replicate a full LOB only. It cannot replicate
parts of a LOB.
- You cannot replicate LOB columns if you use a remote journal setup
in your replication environment on System i®.
- When you use LOBs in update-anywhere
replication, you must set the conflict level to 0.
SQL Replication