What is a Materialized View?
A materialized view is a replica of a
target master from a single point in time. The master can be either a master
table at a master site or a master materialized view at a materialized view
site. Where as in multi master replication tables are continuously updated by
other master sites, materialized views are updated from one or more masters
through individual batch updates, known as a refreshes, from a
single master site or master materialized view site, as illustrated in. The
arrows in represent database links.
Read-Only
Materialized Views
You can make a materialized view read-only during creation
by omitting the FOR UPDATE clause or disabling the equivalent option
in the Replication Management tool.
Updatable
Materialized Views
You can make a materialized view updatable during creation
by including the FOR UPDATE clause or enabling the equivalent
option in the Replication Management tool. For changes made to an updatable
materialized view to be pushed back to the master during refresh, the updatable
materialized view must belong to a materialized view group.
SQL>CREATE MATERIALIZED VIEW hr.departments FOR UPDATE AS SELECT * FROM hr.departments@orc1.world;
Writeable
Materialized Views
A
writeable materialized view is one that is created using
the FOR UPDATE clause but is not part of a materialized view
group. Users can perform DML operations on a writeable materialized view, but
if you refresh the materialized view, then these changes are not pushed back to
the master and the changes are lost in the materialized view itself. Writeable
materialized views are typically allowed wherever fast-refreshable read-only
materialized views are allowed.
Required Privileges
for Materialized View Operations
- Creator: the user who creates the materialized view
- Refresher: the user who refreshes the materialized view
- Owner: the user who owns the materialized view. The materialized view resides in this user's schema.
