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A very small database may need only the SYSTEM tablespace; however, Oraclerecommends that you create at least one additional tablespace to store user dataseparate from data dictionary information. This gives you more flexibility invariousdatabase administration operations and reduces contention among dictionaryobjectsand schema objects for the same datafiles.1. 一个数据库最少需要system表空间2. 使用多个表空间 ， 你可以将用户数据与数据字段分开，减少同一数据文件在系统和用户对象之间的竞争[@m

Specify default temporary tablespaces when you create a database, using the DEFAULT TEMPORARY TABLESPACE extension to the CREATE DATABASE statement.If you drop all default temporary tablespaces, then the SYSTEM tablespace is used as the default temporary tablespace. You can create bigfile temporary tablespaces. A bigfile temporary tablespaces uses tempfiles instead of datafiles.创建临时表空间1. create database 时使用 default temporary tablespaces2. 删除所有临时表空间后 ， system表空间将被成

When the SYSTEM tablespace is locally managed, you must define at least one default temporary tablespace when creating a database. A locally managed SYSTEM tablespace cannot be used for default temporary storage.If SYSTEM is dictionary managed and if you do not define a default temporary tablespace when creating the database, then SYSTEM is still used for default temporary storage. However, you will receive a warning in ALERT.LOG saying that a default temporary tablespace is recommended and will

You assign an undo tablespace to an instance in one of two ways:1 At instance startup. You can specify the undo tablespace in the initialization file or let the system choose an available undo tablespace.2 While the instance is running. Use ALTER SYSTEM SET UNDO_TABLESPACE to replace the active undo tablespace with another undo tablespace. This method is rarely used.You can add more space to an undo tablespace by adding more datafiles to the undo tablespace with the ALTER TABLESPACE statemen

Undo tablespaces are special tablespaces used solely for storing undo information. You cannot create any other segment types (for example, tables or indexes) in undo tablespaces. Each database contains zero or more undo tablespaces. In automatic undo management mode, each Oracle instance is assigned one (and only one) undo tablespace. Undo data is managed within an undo tablespace using undo segments that are automatically created and maintained by Oracle.When the first DML operation is run with

A database administrator creates undo tablespaces individually, using the CREATE UNDO TABLESPACE statement. It can also be created when the database is created, using the CREATE DATABASE statement. A set of files is assigned to each newly created undo tablespace. Like regular tablespaces, attributes of undo tablespaces can be modified with the ALTER TABLESPACE statement and dropped with the DROP TABLESPACE statement.An undo tablespace cannot be dropped if it is being used by any instance or cont

The SYSAUX tablespace is an auxiliary tablespace to the SYSTEM tablespace. Many database components use the SYSAUX tablespace as their default location to store data. Therefore, the SYSAUX tablespace is always created during database creation or database upgrade. The SYSAUX tablespace provides a centralized location for database metadata that does not reside in the SYSTEM tablespace. It reduces the number of tablespaces created by default, both in the seed database and in user-defined databases.

Every Oracle database contains a tablespace named SYSTEM, which Oracle creates automatically when the database is created. The SYSTEM tablespace is always online when the database is open.To take advantage of the benefits of locally managed tablespaces, you can create a locally managed SYSTEM tablespace, or you can migrate an existing dictionary managed SYSTEM tablespace to a locally managed format. In a database with a locally managed SYSTEM tablespace, dictionary managed tablespaces cannot be

A database is divided into one or more logical storage units called tablespaces. Tablespaces are divided into logical units of storage called segments, which are further divided into extents. Extents are a collection of contiguous blocks.database->tablespaces->segments->extents->blocks(contiguous)[@more@]

The size of a tablespace is the size of the datafiles that constitute the tablespace. The size of a database is the collective size of the tablespaces that constitute the database.You can enlarge a database in three ways:1 Add a datafile to a tablespace2 Add a new tablespace3 Increase the size of a datafileWhen you add another datafile to an existing tablespace, you increase the amount of disk space allocated for the corresponding tablespace. Figure 3–2 illustrates this kind of space i

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Oracle-managed files eliminate the need for you, the DBA, to directly manage the operating system files comprising an Oracle database. You specify operations in terms of database objects rather than filenames. Oracle internally uses standard file system interfaces to create and delete files as needed for the following database structures: 1 Tablespaces 2 Redo log files 3 Control files Through initialization parameters, you specify the file system directory to be used for a particular type of

oracle stores data logically in tablespaces and physically in datafiles associated with the corresponding tablespace.datafiles objects(physical structures associated with only one tablespace)objects (stored in tablespaces-may span several datafiles)databases, tablespaces, and datafiles are closely related, but they have important differences:1 an oracle database consists of one or more logical storage units called tablespaces, which collectively store all of the database??s data. 2 each tabl

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在查看SQL语句执行计划时 ， 在Sqlplus下使用set autot traceonlyset longsize 800set autot traceonlyselect">test@ora10g>select * from t_test where tonecode like '501%';已选择5103行。执行计划--------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost(%CPU)|----------------------------------------------------------------------------------| 0

Purpose Use the RENAME statement to rename a table, view, sequence, or private synonym. a. Oracle Database automatically transfers integrity constraints, indexes, and grants on the old object to the new object. b. Oracle Database invalidates all objects that depend on the renamed object, such asviews, synonyms, and stored procedures and functions that refer to a renamed table.Prerequisites The object must be in your own schema.Syntax ren

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show">sys@ora10g>show parameter optimizer_modeNAME TYPE VALUE------------------------------------ ----------- ------------------------------optimizer_mode string all_rows optimizer_mode establishes the default behavior for choosing an optimizationapproach for the instance.Values:■ first_rows_nThe optimizer uses a cost-based approach and optimizes with a goal of bestresponse time to return the first n rows (where n =