Training Test 1

Training Test 1 - Training Test 1 Materialized...

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Training Test 1 Materialized View/Snapshot View : A materialized view can be used to pre- collect aggregate values. A materialized view can be used to assemble data that would come from many different tables, which would in turn require many different joins to be performed. A materialized view is like a view in that it represents data that is contained in other database tables and views; yet it is unlike a view in that it contains actual data. A materialized view is like an index in that the data it contains is derived from the data in database tables and views; yet unlike an index in that its data must be explicitly refreshed. Finally, a materialized view is very much like a snapshot in that an administrator can specify when the data is to be refreshed; but it is unlike a snapshot in that a materialized view should either include summary data or data from many different joined tables. The cost-based optimizer can automatically substitute a materialized view for a standard table or group of tables if appropriate. This capability in the optimizer means that you can add materialized views to your database and reap the performance benefits, without having to rewrite any of your applications. Database Link: Use the CREATE DATABASE LINK statement to create a database link. A database link is a schema object in one database that enables you to access objects on another database. The other database need not be an Oracle Database system. However, to access non-Oracle systems you must use Oracle Heterogeneous Services. Once you have created a database link, you can use it to refer to tables and views on the other database. In SQL statements, you can refer to a table or view on the other database by appending @dblink to the table or view name. You can query a table or view on the other database with the SELECT statement. You can also access remote tables and views using any INSERT , UPDATE , DELETE , or LOCK TABLE statement. Datafile: Datafiles are physical files of the operating system that store the data of all logical structures in the database. They must be explicitly created for each tablespace. Oracle assigns each datafile two associated file numbers, an absolute file number and a relative file number , that are used to uniquely identify it. These numbers are described in the following table: CREATE TABLESPACE tbsb DATAFILE '/u02/oracle/data/tbsa01.dbf' SIZE 50M EXTENT MANAGEMENT DICTIONARY DEFAULT STORAGE ( INITIAL 50K NEXT 50K MINEXTENTS 2 MAXEXTENTS 50 PCTINCREASE 0); ALTER TABLESPACE tbsa ADD DATAFILE '/u02/oracle/data/tbsa02.dbf' SIZE 1M;
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Checkpoint: A checkpoint performs the following three operations: 1. Every dirty block in the buffer cache is written to the data files . That is, it synchronizes the datablocks in the buffer cache with the datafiles on disk.
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