What is a materialized view in Oracle?
A materialized view is a database object that contains the results of a query. You can select data from a materialized view as you would from a table or view. In replication environments, the materialized views commonly created are primary key, rowid, object, and subquery materialized views.
What is oracle mlog?
An MLOG$ table is the Snapshot Log table created against a base table. A row is inserted into the table each time a change (insert/update/delete) is made to the base table.
Why materialized view log is created?
When DML changes are made to master table data, Oracle Database stores rows describing those changes in the materialized view log and then uses the materialized view log to refresh materialized views based on the master table. This process is called incremental or fast refresh.
Does materialized view store data?
A materialized view is a pre-computed data set derived from a query specification (the SELECT in the view definition) and stored for later use. Because the data is pre-computed, querying a materialized view is faster than executing a query against the base table of the view.
How does materialized view improve performance in Oracle?
Materialized views improve query performance by precalculating expensive join and aggregation operations on the database prior to execution and storing the results in the database. The query optimizer automatically recognizes when an existing materialized view can and should be used to satisfy a request.
Can we update a materialized view in Oracle?
Specify COMPLETE for the complete refresh method, which is implemented by executing the defining query of the materialized view. If you specify a complete refresh, Oracle Database performs a complete refresh even if a fast refresh is possible.
How do you make a Mlog?
CREATE MATERIALIZED VIEW LOG ON tableName [WITH [PRIMARY KEY][,ROWID]|[ROWID][,PRIMARY KEY] [(columnName[,…])]] List of columns for which changes will be recorded in the log. Use the WITH clause to indicate the keys and columns for which changes will be recorded in the materialized view log.
How often is materialized view refresh?
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.
Why do we need materialized views?
Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution.