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The Oracle Database provides a Segment Advisor that helps you determine whether an object has space available for reclamation based on the level of space fragmentation within the object.In general, the extents of a segment do not return to the tablespace until you drop the schema object whose data is stored in the segment (using a DROP TABLE or DROP CLUSTER statement). Exceptions to this include the following: ■ The owner of a table or cluster, or a user with the DELETE ANY privilege, can trunc

Oracle uses different algorithms to allocate extents, depending on whether they are locally managed or dictionary managed. With locally managed tablespaces, Oracle looks for free space to allocate to a new extent by first determining a candidate datafile in the tablespace and then searching the datafile’s bitmap for the required number of adjacent free blocks. If that datafile does not have enough adjacent free space, then Oracle looks in another datafile.[@more@]

A tablespace that manages its extents locally can have either uniform extent sizes or variable extent sizes that are determined automatically by the system. When you create the tablespace, the UNIFORM or AUTOALLOCATE (system-managed) clause specifies the type of allocation. ■ For uniform extents, you can specify an extent size or use the default size, which is 1 MB. Ensure that each extent contains at least five database blocks, given the database block size. Temporary tablespaces that manage t

specifies whether or not the export utility uses the set transaction read onlystatement to ensure that the data exported is consistent to a single point in time anddoes not change during the export. if object_consistent is set to y, each objectis exported in its own read-only transaction, even if it is partitioned. in contrast, ifyou use the Consistent parameter, then there is only one read-only transaction.与Consistent参数的区别:1. Object_Consistent是每个导出的对象都有每个对象的consistent2.

Export provides two methods for exporting table data:■ Conventional path Export■ Direct path ExportConventional path Export uses the SQL SELECT statement to extract data fromtables. Data is read from disk into a buffer cache, and rows are transferred to theevaluatingbuffer.Thedata,afterpassingexpressionevaluation,istransferredtotheExport client, which then writes the data into the export file.Direct path Export is much faster than conventional path Export because data isread from disk into the

Specifies whether or not Export uses the SET TRANSACTION READ ONLYstatement to ensure that the data seen by Export is consistent to a single point intime and does not change during the execution of theexp command. You shouldspecifyCONSISTENT=y when you anticipate that other applications will beupdating the target data after an export has started.If you useCONSISTENT=n, each table is usually exported in a single transaction.However, if a table contains nested tables, the outer table and each inne

Specifies how Export and Import manage the initial extent for table data.The default,COMPRESS=y, causes Export to flag table data for consolidation into one initial extent upon Import. If extent sizes are large (for example, because of thPCTINCREASE parameter), the allocated space will be larger than the space required to hold the data.If you specifyCOMPRESS=n, Export uses the current storage parameters, includin the values of initial extent size and next extent size. The values of the parameter

Specifies the size, in bytes, of the buffer used to fetch rows. As a result, this parameter determines the maximum number of rows in an array fetched by Export.Use the following formula to calculate the buffer size:buffer_size = rows_in_array * maximum_row_sizeIf you specify zero, the Export utility fetches only one row at a time.Tables with columns of typeLONG,LOB,BFILE,REF,ROWID,LOGICALROWID, orDATE are fetched one row at a time.Example: Calculating Buffer SizeThis section shows an example of

select">sys@ora10g>select 1 from dual; 1可是heading明明设置为onshow">sys@ora10g>show headingheading ON原来当pages参数设置为0的时候,标题栏也是显示不出来的.改为其他值后,即可显示.show">sys@ora10g>show pagespagesize 0set">sys@ora10g>set pages 50000select">sys@ora10g>select 1 from dual; 1---------- 1 谢谢yangtingkun指教[@more@]Sqlplus查询时标题栏不能显示

If the number of distinct values of a column is less than 1% of the number of rows in the table, or if the values in a column are repeated more than 100 times, then the column is a candidate for a bitmap index.a bitmap index on this column can out-perform a b-tree index, particularly when this column is often queried in conjunction with other columns.[@more@]

不管用什么as sysdba,最终都归于以sys用户登录1 conn其他用户conn">sys@ora10g>conn ring/ring as sysdba已连接。show">sys@ora10g>show userUSER 为 "SYS"2 其他用户以sysdba登录sqlplus ring as sysdbaSQL*Plus: Release 10.2.0.1.0 - Production on 星期二 8月 28 23:29:16 2007Copyright (c) 1982, 2005, Oracle. All rights reserved.输入口令:连接到:Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - ProductionWith the Partitioning, OLAP and Data Mining optionsshow">sys@ora10g&g

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这几天工作上出了点问题,个人觉得有以下方面需要改进:1 权责最好相等2 给与他人及时表扬,关注他人3 一次认真做完一个事4 以专家权来指导下属,以典范权来督促下属行动[@more@]

When you create a table, Oracle allocates to the table’s data segment an initial extentof a specified number of data blocks.An incremental extent is a subsequent extent of the same or greater size thanthe previously allocated extent in that segment.For maintenance purposes, the header block of each segment contains a directory ofthe extents in that segment.[@more@]

An extent is a logical unit of database storage space allocation made up of a number ofcontiguous data blocks.[@more@]

一般地，大家都认为Yahoo(雅虎)邮件只能够通过Web方式收取和发送，于是，许多喜爱使用outlook/Foxmail管理邮件的网友不得不舍弃了Yahoo邮箱。其实，Yahoo提供了一个免费的“网上直投”功能，可以让您使用Foxmail、Outlook收发Yahoo邮件。只是这个功能在网站上没有连接，只有缴费后才能用。不过，我们有办法。　　要使用这项功能，必须先注册成为Yahoo“网上直投”的成员，具体方法如下：　　1. 启动IE浏览器，登录您的Yahoo邮箱。(注意:必须是中国yahoo)　　2. 在地址栏中键入http://edit.my.yahoo.com/config/set_popfwd?.src=ym&don

In a newly allocated data block, the space available for inserts is the block size minusthe sum of the block overhead and free space (PCTFREE).free lists—lists ofdata blocks that have been allocated for that segment’s extents and have free spacegreater than PCTFREE. These blocks are available for inserts. When you issue anINSERT statement, Oracle checks a free list of the table for the first available data blockand uses it if possible. If the free space in that block is not large enough toacco

The PCTUSED parameter sets the minimum percentage of a block that can be used forrow data plus overhead before new rows are added to the block. After a data block isfilled to the limit determined by PCTFREE, Oracle considers the block unavailable for the insertion of new rows until the percentage of that block falls beneath the parameterPCTUSED. Until this value is achieved, Oracle uses the free space of the data block onlyfor updates to rows already contained in the data block.[@more@]

The PCTFREE parameter sets the minimum percentage of a data block to be reservedas free space for possible updates to rows that already exist in that block.Newrows can be added to the row data area, and corresponding information can be addedto the variable portions of the overhead area, until the row data and overhead total (100-PCTFREE )% of the total block size[@more@]

For manually managed tablespaces, two space management parameters, PCTFREEand PCTUSED, enable you to control the use of free space for inserts and updates to therows in all the data blocks of a particular segment.[@more@]