April 1999
Intermediate to advanced
552 pages
15h 39m
English
Content preview from Oracle Distributed Systems
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Options for Distributed Data
Oracle provides several methods for accessing data that is distributed among two or more database instances. All of these methods provide location transparency , which means that users and applications can manipulate data as though it were all in one single database instance. These various methods are summarized here and are described in detail throughout this book.
Export/Import
The Oracle export and import utilities (illustrated in Figure 1.4) are the most primitive
method of sharing data among databases and are also used as part of
a backup and recovery strategy. Export (exp)
creates a file that is essentially a set of SQL statements that
invoke the DDL (Data Description Language) and DML (Data
Manipulation Language) required to create objects and insert data.
Import (imp) is the utility that reads this
file and executes the SQL statements to re-create the objects and
populate tables. A full database export creates a file that you can
use to re-create the entire database.
Figure 1-4. Export/import
Unlike any of the other options, export and import are static. An export file contains the data from the time of the export and cannot be updated. In fact, an export file could easily be out of date before the export job is finished. In addition, you must specify the export option CONSISTENT=Y in order for all of the data in the export file to be consistent ...
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