The more frequently all the materialized
views that reference the master table are refreshed, the less space is needed for the log.
Chapter 17: Managing Distributed Databases 625
You can modify the storage parameters for the materialized view log via the alter materialized
view log command. When using this command, specify the name of the master table. An example
of altering the EMPLOYEES table??™s materialized view log is shown in the following listing:
alter materialized view log on EMPLOYEES pctfree 10;
To drop a materialized view log, use the drop materialized view log command, as in this
example:
drop materialized view log on EMPLOYEES;
Purging the Materialized View Log
The materialized view log contains transient data; records are inserted into the log, used during
refreshes, and then deleted. If multiple materialized views use the same master table, they share
the same materialized view log. If one of the materialized views is not refreshed for a long period,
the materialized view log may never delete any of its records. As a result, the space requirements
of the materialized view log will grow.
To reduce the space used by log entries, you can use the PURGE_LOG procedure of the
DBMS_MVIEW package. PURGE_LOG takes three parameters: the name of the master table,
a num variable, and a DELETE flag. The num variable specifies the number of least recently
refreshed materialized views whose rows will be removed from the materialized view log.
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