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Oracle mlog$ tips

Oracle Database Tips by Donald BurlesonApril 1, 2015

Question:  What are he Oracle mlog$ tables and how are they used with materialized views?  Is there an mlog$ table for every table in a materialized view'stote

Answer:  One mlog$ table exists for every table that participates in a materialized view, with the name mlog$_tablename.  These mlog$ tables serve to store all DML changes that will be transported to a materialized view with the :refresh fast: option.

Oracle materialized view mlog$ table

The mlogs$_ is the materialized view log created with the CREATE MATERIALIZED VIEW LOG command. Note that materialized view log tables using primary keys also have rupd$_ tables, as is the case in this example. The rupd$_ table supports updateable materialized views, which are only possible on log tables with primary keys.

The materialized view logs are just like any other table and can be queried.

SQL> desc mlog$_bonus;

Name Null? Type
---------------------------- -------- -------------
M_ROW$$                      VARCHAR2(255)
SNAPTIME$$                   DATE
DMLTYPE$$                    VARCHAR2(1)
OLD_NEW$$                    VARCHAR2(1)
CHANGE_VECTOR$$              RAW(255)

Execute a select count(*) to determine whether there are changes waiting to propagate.

SQL> select count(*) from mlog$_bonus;

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