| Oracle® Database Concepts 10g Release 2 (10.2) Part Number B14220-02 |
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View PDF |
| Oracle® Database Concepts 10g Release 2 (10.2) Part Number B14220-02 |
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View PDF |
This chapter describes Oracle database utilities for data transfer, data maintenance, and database administration.
This chapter contains the following topics:
Oracle's database utilities let you perform the following tasks:
High-speed movement of data and metadata from one database to another using Data Pump Export and Import
Extract and manipulate complete representations of the metadata for database objects, using the Metadata API
Move all or part of the data and metadata for a site from one database to another, using the Data Pump API
Load data into Oracle tables from operating system files using SQL*Loader or from external sources using external tables
Query redo log files through a SQL interface with LogMiner
Perform physical data structure integrity checks on an offline (for example, backup) database or datafile with DBVERIFY.
Maintain the internal database identifier (DBID) and the database name (DBNAME) for an operational database, using the DBNEWID utility
Oracle Data Pump technology enables very high-speed movement of data and metadata from one database to another. This technology is the basis for Oracle's data movement utilities, Data Pump Export and Data Pump Import.
Data Pump enables you to specify whether a job should move a subset of the data and metadata. This is done using data filters and metadata filters, which are implemented through Export and Import parameters.
Data Pump Export (hereinafter referred to as Export for ease of reading) is a utility for unloading data and metadata into a set of operating system files called a dump file set. The dump file set can be moved to another system and loaded by the Data Pump Import utility.
The dump file set is made up of one or more disk files that contain table data, database object metadata, and control information. The files are written in a proprietary, binary format, which can be read only by Data Pump Import. During an import operation, the Data Pump Import utility uses these files to locate each database object in the dump file set.
Data Pump Import (hereinafter referred to as Import for ease of reading) is a utility for loading an export dump file set into a target system. The dump file set is made up of one or more disk files that contain table data, database object metadata, and control information. The files are written in a proprietary, binary format.
Import can also be used to load a target database directly from a source database with no intervening files, which allows export and import operations to run concurrently, minimizing total elapsed time. This is known as network import.
Import also enables you to see all of the SQL DDL that the Import job will be executing, without actually executing the SQL. This is implemented through the Import SQLFILE parameter.
The Data Pump API provides a high-speed mechanism to move all or part of the data and metadata for a site from one database to another. To use the Data Pump API, you use the procedures provided in the DBMS_DATAPUMP PL/SQL package. The Data Pump Export and Data Pump Import utilities are based on the Data Pump API.
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The Metadata application programming interface (API), provides a means for you to do the following:
Retrieve an object's metadata as XML
Transform the XML in a variety of ways, including transforming it into SQL DDL
Submit the XML to re-create the object extracted by the retrieval
To use the Metadata API, you use the procedures provided in the DBMS_METADATA PL/SQL package. For the purposes of the Metadata API, every entity in the database is modeled as an object that belongs to an object type. For example, the table scott.emp is an object and its object type is TABLE. When you fetch an object's metadata you must specify the object type.
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SQL*Loader loads data from external files into tables of an Oracle database. It has a powerful data parsing engine that puts little limitation on the format of the data in the datafile. You can use SQL*Loader to do the following:
Load data from multiple datafiles during the same load session.
Load data into multiple tables during the same load session.
Specify the character set of the data.
Selectively load data (you can load records based on the records' values).
Manipulate the data before loading it, using SQL functions.
Generate unique sequential key values in specified columns.
Use the operating system's file system to access the datafiles.
Load data from disk, tape, or named pipe.
Generate sophisticated error reports, which greatly aids troubleshooting.
Load arbitrarily complex object-relational data.
Use secondary datafiles for loading LOBs and collections.
Use either conventional or direct path loading. While conventional path loading is very flexible, direct path loading provides superior loading performance.
A typical SQL*Loader session takes as input a control file, which controls the behavior of SQL*Loader, and one or more datafiles. The output of SQL*Loader is an Oracle database (where the data is loaded), a log file, a bad file, and potentially, a discard file.
The external tables feature is a complement to existing SQL*Loader functionality. It lets you access data in external sources as if it were in a table in the database. External tables can be written to using the ORACLE_DATAPUMP access driver. Neither data manipulation language (DML) operations nor index creation are allowed on an external table. Therefore, SQL*Loader may be the better choice in data loading situations that require additional indexing of the staging table.
To use the external tables feature, you must have some knowledge of the file format and record format of the datafiles on your platform. You must also know enough about SQL to be able to create an external table and perform queries against it.
Oracle LogMiner enables you to query redo log files through a SQL interface. All changes made to user data or to the database dictionary are recorded in the Oracle redo log files. Therefore, redo log files contain all the necessary information to perform recovery operations.
LogMiner functionality is available through a command-line interface or through the Oracle LogMiner Viewer graphical user interface (GUI). The LogMiner Viewer is a part of Oracle Enterprise Manager.
The following are some of the potential uses for data contained in redo log files:
Pinpointing when a logical corruption to a database, such as errors made at the application level, may have begun. This enables you to restore the database to the state it was in just before corruption.
Detecting and whenever possible, correcting user error, which is a more likely scenario than logical corruption. User errors include deleting the wrong rows because of incorrect values in a WHERE clause, updating rows with incorrect values, dropping the wrong index, and so forth.
Determining what actions you would have to take to perform fine-grained recovery at the transaction level. If you fully understand and take into account existing dependencies, it may be possible to perform a table-based undo operation to roll back a set of changes.
Performance tuning and capacity planning through trend analysis. You can determine which tables get the most updates and inserts. That information provides a historical perspective on disk access statistics, which can be used for tuning purposes.
Performing post-auditing. The redo log files contain all the information necessary to track any DML and DDL statements run on the database, the order in which they were run, and who executed them.
DBVERIFY is an external command-line utility that performs a physical data structure integrity check. It can be used on offline or online databases, as well on backup files. You use DBVERIFY primarily when you need to ensure that a backup database (or datafile) is valid before it is restored or as a diagnostic aid when you have encountered data corruption problems.
Because DBVERIFY can be run against an offline database, integrity checks are significantly faster.
DBVERIFY checks are limited to cache-managed blocks (that is, data blocks). Because DBVERIFY is only for use with datafiles, it will not work against control files or redo logs.
There are two command-line interfaces to DBVERIFY. With the first interface, you specify disk blocks of a single datafile for checking. With the second interface, you specify a segment for checking.
DBNEWID is a database utility that can change the internal, unique database identifier (DBID) and the database name (DBNAME) for an operational database. The DBNEWID utility lets you change any of the following:
Only the DBID of a database
Only the DBNAME of a database
Both the DBNAME and DBID of a database
Therefore, you can manually create a copy of a database and give it a new DBNAME and DBID by re-creating the control file, and you can register a seed database and a manually copied database together in the same RMAN repository.
