Home » Oracle » 1z0-117 » Which four must be true to enable sessions to benefit from improved response time made possible by these materialized views?
You have created some materialized views to improve the performance of several queries.
Which four must be true to enable sessions to benefit from improved response time made possible by these materialized views?
A. Query rewrite must be enabled for the sessions.
B. Bitmap indexes must exist on all the columns involved in the join operations for the defining query of the MVIEWs.
C. All or part of the query results must be obtainable from one or more MVIEWs.
D. Bitmap join indexes must exist on all the columns involved in the join operations.
E. Session users must have query rewrite privilege.
F. The MVIEWs must be enabled for query rewrite.
G. All or part of the query results must be obtainable from one MVIEW.
Correct Answer: ABCF
Explanation/Reference:
A:For a given user’s session, ALTER SESSION can be used to disable or enable query rewrite for that session only.
B: Bitmap indexes on the join columns would improve performance.
C(notG) :One of the major benefits of creating and maintaining materialized views is the ability to take advantage of query rewrite, which transforms a SQL statement expressed in terms of tables or views into a statement accessing one or more materialized views that are defined on the detail tables.
F:
*A materialized view is only eligible for query rewrite if the ENABLE QUERY REWRITE clause has been specified, either initially when the materialized view was first created or subsequently with an ALTER MATERIALIZED VIEW statement.
*Enabling or disabling query rewrite:
by the CREATE or ALTER statement for individual materialized views
by the initialization parameter QUERY_REWRITE_ENABLED
by the REWRITE and NOREWRITE hints in SQL statements
Note:
*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. Whereas in multimaster 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.
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