Sage-Tips

What does refresh materialized view do?

REFRESH MATERIALIZED VIEW completely replaces the contents of a materialized view. To execute this command you must be the owner of the materialized view. The old contents are discarded. If WITH NO DATA is specified no new data is generated and the materialized view is left in an unscannable state.

What is Oracle materialized view refresh?

A materialized view, or snapshot as they were previously known, is a table segment whose contents are periodically refreshed based on a query, either against a local or remote table. Using materialized views against remote tables is the simplest way to achieve replication of data between sites.

Why do we use materialized view in Oracle?

Oracle uses materialized views (also known as snapshots in prior releases) to replicate data to non-master sites in a replication environment and to cache expensive queries in a data warehouse environment.

What is the necessity of using materialized view?

In data warehouses, you can use materialized views to precompute and store aggregated data such as the sum of sales. Materialized views in these environments are often referred to as summaries, because they store summarized data. They can also be used to precompute joins with or without aggregations.

How does materialized view improve performance in Oracle?

There are several options:

1. – Partition the base tables – See notes below on hoe partition pruning makes materialized view refreshes run faster.
2. – Use parallel DML – Oracle author Michael Armstrong Smith notes “I’ve done parallel materialized view refreshing on tables recently and improved the load times considerably.

What is the difference between fast refresh and complete refresh in materialized view?

“Complete Refresh” means you truncate entire materialized view and insert new data. “Fast Refresh” means you update (or insert/delete) only the rows which have been changed on master tables.

How do you maintain materialized views we can use?

To maintain materialized views, we can use

1. ✅ Triggers.
2. Pointers.
3. Cascading.

Are materialized views good?

Advantages of Materialized Views Materialized views can improve the performance of queries that use the same subquery results repeatedly. Materialized views are automatically and transparently maintained by Snowflake. A background service updates the materialized view after changes are made to the base table.

How can check materialized view refresh status?

select * from dba_refresh;select * from dba_refresh_children; select * from sys. v_$mvrefresh; Then below query to find the status of job.

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.

How do I optimize a materialized view refresh?

Boost up materialized view refreshes: – Partition the base tables – Do a partition for remote/ base table. Use efficient partition. See my notes on partition in this blog. – Use parallel DML – Use parallel materialized view refreshing on tables.

Do we need to refresh materialized view?

Oracle uses materialized views(also known as snapshots in prior releases) to replicate data to non-master sites in a replication environment and to cache expensive queries in a data warehouse environment. This chapter, and this Oracle9i Replicationmanual in general, discusses materialized views for use in a replication environment.

Can we use create or replace materialized view?

No, we can’t use create or replace option with materialised voews. To replace such views we must drop them first and recreate them.

Is materialized view refreshed automatically?

A materialized view can be refreshed automatically. It depends on how it was defined. If it was defined as refresh on commit, it is refreshed automatically, otherwise it is refreshed on some sort of schedule. A normal view is not refreshed automatically.

What is materialize hint in Oracle?

Note the use of the Oracle undocumented materialize hint in the WITH clause. The Oracle materialize hint is used to ensure that the Oracle CBO materializes the temporary tables that are created inside the WITH clause, and its opposite is the undocumented inline hint.