Autonomous Schema Update (ASU) functions differently when working with a read-only replication target database. As the target replication database is read-only, the schema cannot be updated. In the event of a SQL width problem caused by SQL reporting applications on the replication target, ASU will create DDL commands on the replication target database to address the SQL width issues. These DDL statements are ALTER statements and the syntax is as follows:

ALTER TABLE <table-name> ALTER COLUMN <column-name> SET PRO_SQL_WIDTH <column_width>;
These statements are written to a log file when ASU is enabled on the replication target DB. The log file name will follow the naming convention as SQL_asu_alter_commands_<serverpid>_<timestamp>_A.log and a second log file with the name SQL_asu_alter_commands_<serverpid>_<timestamp>_B.log. The log files have a size limit of 500MB and once the size limit is exceeded, logging happens in the second log file. Once the second log file size exceeds 500MB, the first log file will be overwritten. These files are shared across sessions for the same database. Users should then manually run the DDL commands from the log file on the replication source database using a tool like SQL explorer. Only users with SQL DBA access on the replication source can perform these actions.
Note: Logging is on by default and users can choose to either turn logging on or off using the following statements: 
SET PRO_ASU_REPLICATION_SERVER LOG ON;
to turn logging on and 
SET PRO_ASU_REPLICATION_SERVER LOG OFF;
to turn off logging.