Databases Reference
In-Depth Information
Summary
Sometimes, the term
materialized view
confuses people who are new to the technology. Perhaps Oracle should have
named this feature “periodically purge and repopulate a table that contains the results of a query,” but that's probably
too long a phrase. Regardless, when you understand the power of this tool, you can use it to replicate and aggregate
large amounts of data. You can greatly improve the performance of queries by periodically computing and storing the
results of complex aggregations of data.
MVs can be fast refreshable, which means that they copy over only changes from the master table that have
occurred since the last refresh. To use this type of MV, you must create an MV log on the master table. It's not always
possible to create an MV log; in these scenarios the MV must be completely refreshed.
If need be, you can also compress and encrypt the data with an MV. This allows for better space management
and security. Additionally, you can partition the underlying table used by an MV, to allow for greater scalability,
performance, and availability.
The last several chapters have focused on specialized database features that DBAs often use. These include large
objects, partitioning, Data Pump, external tables, and MVs. The book now shifts focus to one of the most important
topics a DBA must be familiar with: backup and recovery. User managed backups and RMAN are covered in the next
several chapters.
