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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

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@]

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@]

In two circumstances, the data for a row in a table may be too large to fit into a singledata block. the first is case, the row is too large to fit into one data block when it is firstinserted. In this case, Oracle stores the data for the row in a chain of data blocks (oneor more) reserved for that segment.Row chaining most often occurs with large rows such as long ,long raw ,unavoidable.thsi second is a row that originally fit into one data block is updated sothat the overall row length incre

Two types of statements can increase the free space of one or more data blocks:DELETE statements, and UPDATE statements that update existing values to smallervalues.The released space from these types of statements is available for subsequentINSERT statements under the following conditions:■ If the INSERT statement is in the same transaction and subsequent to thestatement that frees space, then the INSERT statement can use the space madeavailable.■ If the INSERT statement is in a separate tran

Free space can be managed automatically or manually. The in-segmentfree/used space is tracked using bitmaps, as opposed to free lists.segment-space management offers the following benefits:■ Ease of use■ Better space utilization, especially for the objects with highly varying row sizes■ Better run-time adjustment to variations in concurrent access■ Better multi-instance behavior in terms of performance/space utilization[@more@]

The Oracle data block format is similar regardless of whether the data block contains table, index, or clustered data.Headergeneral block information, such as the block address and the type of segment (for example, data or index).Table Directorytable having rows in this block.Row DirectoryAfter the space has been allocated in the row directory of a data block’s overhead, this space is not reclaimed when the row is deleted. Oracle reuses this space only when new rows are inserted in the block.Ov

A data block is the smallest unit of data used by a database.In contrast, at the physical, operating system level, all data is stored in bytes. Oracle requests data in multiples of Oracle data blocks, not operating system blocks.you can specify of up to five nonstandard block sizes.The data block sizes should be a multiple of the operating system’s block size within the maximum limit to avoid unnecessary I/O[@more@]

近期将阅读的Oracle10g Concepts中值得注意的地方帖出来,督促自己不断学习进步Introduction to Data Blocks, Extents, and Segments1. Oracle stores data in data blocks (also called logical blocks, Oracle blocks, or pages)2. An extent is a specific number of contiguous data blocks allocated for storing a specific type of information.3. A segment is a set of extents,are stored in the same tablespace.each table's data is stored in its own data segment, while each index's data is stored in its own index seg

1) show parameter sga_max_size2) select name,display_value from v$parameter where name = 'sga_max_size';9i则为select name,value from v$parameter where name = 'sga_max_size';可以用select name,value,display_value from v$parameterwhere value!=display_value;来证实[@more@]

有时候想知道某字段有几个不同的值需要使用select distinct <column_name> from <table_name>来查询该字段不同值,但是对大表来说就进行了全表扫描，增加了系统的负担；如果这张表分析后(10g自动分析)，可以通过如下语句查询:select num_distinct from user_tab_col_statistics where table_name=upper('<table_name>') and column_name=upper('<column_name>')来避免全表扫描[@more@]