Which of the following is necessary to do fast refresh on a materialized view?
For fast refresh to be possible, the SELECT list must contain all of the GROUP BY columns (if present), and there must be a COUNT(*) and a COUNT(column) on any aggregated columns. Also, materialized view logs must be present on all tables referenced in the query that defines the materialized view.
What is refresh force on demand in materialized view?
That means that the data in the materialized view will be deleted, the underlying query will be re-executed, and the results will be loaded into the materialized view.
What are the methods to refresh materialized view?
- Query Rewrite Method 1: Text Match Rewrite.
- Query Rewrite Method 2: Join Back.
- Query Rewrite Method 3: Aggregate Computability.
- Query Rewrite Method 4: Aggregate Rollup.
- Query Rewrite Method 5: Rollup Using a Dimension.
- Query Rewrite Method 6: When Materialized Views Have Only a Subset of Data.
What is faster join or subquery?
Advantages Of Joins: The advantage of a join includes that it executes faster. The retrieval time of the query using joins almost always will be faster than that of a subquery. By using joins, you can maximize the calculation burden on the database i.e., instead of multiple queries using one join query.
How does Oracle choose the refresh method?
), Oracle chooses the refresh method based on the following attempt order: log-based fast refresh, PCT refresh, and complete refresh. Alternatively, you can request the PCT method ( method => ‘P’ ), and Oracle uses the PCT method provided all PCT requirements are satisfied.
When should I use on commit fast refresh in Oracle?
If you anticipate performing insert, update or delete operations on tables referenced by a materialized view concurrently with the refresh of that materialized view, and that materialized view includes joins and aggregation, Oracle recommends you use ON COMMIT fast refresh rather than ON DEMAND fast refresh.
How do I refresh the on demand materialized views?
In the case of ON DEMAND materialized views, the refresh can be performed with refresh methods provided in either the DBMS_SYNC_REFRESH or the DBMS_MVIEW packages: The DBMS_SYNC_REFRESH package contains the APIs for synchronous refresh, a new refresh method introduced in Oracle Database 12c, Release 1.
Why is the only refresh method available for an already built view?
There are, however, cases when the only refresh method available for an already built materialized view is complete refresh because the materialized view does not satisfy the conditions specified in the following section for a fast refresh. Most data warehouses have periodic incremental updates to their detail data.