What are the restrictions for fast refresh materialized views with subqueries?
General Restrictions on Fast Refresh The materialized view must not contain references to non-repeating expressions like SYSDATE and ROWNUM. The materialized view must not contain references to RAW or LONG RAW data types. It cannot contain a SELECT list subquery.
What does a fast refresh means in materialized view?
Materialized views can be refreshed in two ways: fast or complete. A fast refresh requires having a materialized view log on the source tables that keeps track of all changes since the last refresh, so any new refresh only has changed (updated, new, deleted) data applied to the MV.
What is enable fast refresh materialized view in Oracle?
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 true about materialized view complete refresh?
Complete Refresh It loads the contents of a materialized view from scratch. This means, if the SQL query of the materialized view has an execution time of two hours, the Complete Refresh takes at least two hours as well – or ofter even longer.
How does materialized view improve performance in Oracle?
Using Materialized Views to Improve Oracle Database 12c Performance
- You can perform most DML and query commands such as insert, delete, update, and select.
- They can be partitioned.
- They can be compressed.
- They can be parallelized.
- You can create indexes on them.
How can you tell when a materialized view was last refreshed?
- to_char(last_refresh_date, ‘yyyymmddhh24miss’) LAST_REFRESH_DATE.
- FROM all_mviews.
- WHERE owner = ‘MY_OWNER_NAME’
- AND mview_name = ‘MY_MATERIALIZED_VIEW_NAME’
What is the usage of Purge_mview_from_log?
If the materialized view specified is the oldest materialized view to have refreshed from any of the master tables or master materialized views, then the materialized view log is also purged. This procedure does not unregister the materialized view.
How do you check if materialized view is refreshed or not?
select * from dba_refresh;select * from dba_refresh_children; select * from sys. v_$mvrefresh; Then below query to find the status of job.
Do we need to refresh materialized view?
Unlike indexes, materialized views are not automatically updated with every data change. They must explicitly be refreshed, either on every commit, on a periodically time schedule or – typically in data warehouses – at the end of an ETL job.
How do I optimize a materialized view refresh?
– Use super-fast solid-state disks – The easiest and most reliable way is to speed-up a materialized view refresh is to move the target tables and MV’s to SSD. SSD runs several hundred times faster than platter disk, and it plops right in, just a few hours to install.