Materialized View Log options

Question

I have read the documentation. I know you can specify options such as 'with primary key' and/or 'with rowid' when creating a materialized view log. Also, that you can specify to include additional columns in the log -and that these can then be seen in the MLOG$ table that gets created. But I don't know why or in what circumstances you'd specify the one or the other, or include columns or not. Can anyone give some example scenarios where you'd do one or the other?

Answer 1

Hello again,
The fundamental reason (why you would specify primary key and/or ROWID) is to facilitate fast refreshes (as opposed to a complete refresh) of the materialized view -- a lot will depend on the MV query itself, and whether one or both of primary key & ROWID are needed, i.e., if there's a COUNT(*) involved, where the primary key would play a role, or without such an aggregate, the ROWID will be necessary (in any case) for fast refresh.
Edited by: SeánMacGC on Jul 9, 2009 5:54 PM
If you run the utlxmv.sql script in $ORACLE_HOME/rdbms/admin, that will create the MV_CAPABILITIES_TABLE, which when you create an MV and execute DBMS_MVIEW.EXPLAIN_MVIEW('your_mview') will populate that with what that MV is capable of, i.e.,
SQL> desc mv_capabilities_table;
Name                                      Null?    Type
STATEMENT_ID                                       VARCHAR2(30)
MVOWNER                                            VARCHAR2(30)
MVNAME                                             VARCHAR2(30)
CAPABILITY_NAME                                    VARCHAR2(30)
POSSIBLE                                           CHAR(1)
RELATED_TEXT                                       VARCHAR2(2000)
RELATED_NUM                                        NUMBER
MSGNO                                              NUMBER(38)
MSGTXT                                             VARCHAR2(2000)
SEQ                                                NUMBER
SQL> select capability_name, possible from mv_capabilities_table;
CAPABILITY_NAME                P
PCT                            N
REFRESH_COMPLETE               Y
REFRESH_FAST                   N
REWRITE                        N
PCT_TABLE                      N
REFRESH_FAST_AFTER_INSERT      N
REFRESH_FAST_AFTER_ONETAB_DML  N
REFRESH_FAST_AFTER_ANY_DML     N
REFRESH_FAST_PCT               N
REWRITE_FULL_TEXT_MATCH        N
REWRITE_FULL_TEXT_MATCH        N
REWRITE_PARTIAL_TEXT_MATCH     N
REWRITE_PARTIAL_TEXT_MATCH     N
REWRITE_GENERAL                N
REWRITE_GENERAL                N
REWRITE_PCT                    N
PCT_TABLE_REWRITE              N