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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@]

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

1、养成做好每一件事的习惯最成功最快的方式就是做好每件当前的事情或工作。2、学习的习惯。学历代表过去，只有学习才代表未来。3、养成让别人指使你的习惯创造让别人指使你的理由和条件，就等于创造成功的机会4、写总结计划的习惯。有计划领导别人，没计划被别人领导5、发现问题的习惯发现问题是一种素质，解决问题是一种能力6、承担责任的习惯你有多大成就取决于你有多少责任7、主动汇报工作的习惯在你汇报之前，领导就开始问你，那么你的高度就会瞬间下降50%8、尊时守时的习惯尊时守时体现出一个人对事情的基本态度9、自律的习惯有一次

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

中国人不了解他们作为社会个体应该对国家和社会所承担的责任和义务普通中国人通常只关心他们的家庭和亲属，中国的文化是建立在家族血缘关系上而不是建立在一个理性的社会基础之上。中国人只在乎他们直系亲属的福址，对与自己毫不相关的人所遭受的苦难则视而不见毫无疑问，这种以血缘关系为基础的道德观势必导致自私，冷酷。这种自私和冷酷已经成为阻碍中国社会向前发展的最关键因素中国从来就没有成为一个法制社会，因为中国人的思维方式与守法行为格格不入。中国人老想走捷径。他们不明白这样一个事实：即成就来自于与努力工作和牺牲中国

女朋友希望我看的一篇文章,帖出来.一位老师正在给学生讲解如何处理压力。他把一杯水举起来，问大家：“你们估计这杯水会有多重？”学生们的答案从20克到500克不等。“这杯水的重量其实由你举的时间来决定，而与它的实际重量无关。我要是举一分钟，肯定没问题；但要是举一小时，手臂就会酸疼；若举一天，那你们就该叫救护车了。它的实际重量并没有改变，只是我举的时间越长，就会越觉得它沉重。“如果我们始终都肩负担子，总会有熬不住的时候，担子也变得更加沉重。“你只需放下杯子，歇息一会儿后再举起来。”我们一定要不时地将负担放下，

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@]

今天看了<unix高手的十大习惯>一文 ，发现自己在使用时有些地方存在着"不良的使用模式","不良的使用模式会降低速度，并且通常会导致意外错误"，现将其对应好习惯列出来，方便自己"不良的使用模式"得到改正.1 使用mkdir -p建立目录树 mkdir -p project/{lib/ext,bin,src,doc/{html,info,pdf},demo/stat/a}2 使用tar -C 将.tar文件解压缩到任何目录tar xvf -C tmp/a/b/c newarc.tar.gz3 使用grep -c来进行计数 grep -c and tmp/a/longfile.txt4 使用 awk 代替grep 来查找特定字段中的模式 l

lc命令介绍1 在unix和windows环境下是一个交互式的命令2 输出是根据类型来输出的，通常情况下是根据文件或者是文件夹3 在windows环境下，系统的，隐藏的，和只读文件和文件家是分开显示的lc命令参数介绍-a 显示所有的文件和文件夹(包括以"."命令开始的).-d 只显示文件夹-f 只显示文件-n 隐藏所有输出-1 一行显示一个文件想知道某文件夹下面有什么文件夹，就可以使用lc -deg:C:>lc -dDirectories:Documents and Settings Perl WINDOWSRead-Only Directories:Program Files[@more@]

1) where前面要带双引号2) to_date参数需要从单引号变成双音号3) exp支持的userid格式username/userpassword@tnsname , 不支持username@tnsname/userpassword格式eg:exp userid=test/test@ora92 file=t_test.dmp buffer=40768000 tables=(t_test) query='"where time1>=to_date(''20070601'',''yyyymmdd'') and time2<to_date(''20070701'',''yyyymmdd'')"'[@more@]