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>> 关于ROLLBACK SEGMENT [<a href=http://www.jsp001.com/forum/showthread.php?goto=newpost&threadid=309>查看别人的评论</a>]<br>
<hr><p>由 webmaster 发布于: 2001-02-07 14:23</p><p><img src="images/icons/icon6.gif" alt="Cool" border=0> </p><p>rollback segment是ORACLE里一种很特殊的数据对象，它处理事务的回滚操作。<br><br>通常，我们需要（并发ORACLE用户连接数/4 ） 个rollback segment，一般用private类型, 最大的个数为50。<br><br>创建r01,r02,r03,r04以外的rollback segment语法：<br><br>create rollback segment r05 tablespace rbs storage (initial 128k next 128k minextents 20 );<br>alter rollback segment r05 online;<br>...... ......<br><br>rollback segemt 缺省的存储参数：pctincrease 0 minextents 偶数 <br> maxextent跟数据库的块大小有关<br> 2K 121<br> 4K 249<br> 8K 505<br><br>针对某个特定的大事务操作，如update大量数据时，可以建一个大的rollback segment<br><br>如：<br>create rollback segment rte tablespace rbs storage (initial 5M next 5M minextents 20);<br>alter rollback segment rte online;<br>改数据库参数文件 initoraid.ora<br>rollback_segments = (r01, r02, r03, r04,r05,r06,r07,r08,r09,r10,r11,r12,rte)<br><br>重启数据库,新建的rollback_segment才生效<br><br>把大事务操作指给大的回滚段rte<br>set transction use rollback_segment rte;<br>update table_name set filed_name=...... where ...... ;<br>commit;<br></p></td>
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