Oracle中IMU技术和redo private strand技术

oracle030

oracle030Oracle中IMU技术和redo private strand技术







3、图解Oracle IMU机制

select * from v$sysstat where name like '%IMU%';

STATISTIC#, NAME,    CLASS, VALUE, STAT_ID 312 IMU commits 128 393 1914489094 313 IMU Flushes 128 88 2099506212 314 IMU contention 128 1 2909373607 315 IMU recursive-transaction flush 128 2 2591100633 316 IMU undo retention flush 128 0 2087226422 317 IMU ktichg flush 128 0 1206609541 318 IMU bind flushes 128 0 2756376339 319 IMU mbu flush 128 0 3723686946 320 IMU pool not allocated 128 0 659017805 321 IMU CR rollbacks 128 114 2225124543 322 IMU undo allocation size 128 1867712 244193920 323 IMU Redo allocation size 128 161408 3945654623 324 IMU- failed to get a private strand 128 0 2412863545

4、图解Oracle private redo strands机制

查看回滚段的使用情况，哪个用户正在使用回滚段的资源 select s.username, u.name from v$transaction t,v$rollstat r, v$rollname u,v$session s where s.taddr=t.addr and t.xidusn=r.usn and r.usn=u.usn order by s.username; 检查UNDO Segment状态 select usn,xacts,rssize/1024/1024/1024,hwmsize/1024/1024/1024,shrinks from v$rollstat order by rssize; 确定当前例程正在使用的UNDO表空间 Show parameter undo_tablespace 显示数据库的所有UNDO表空间 SELECT tablespace_name FROM dba_tablespaces WHERE contents='UNDO'; 显示UNDO表空间统计信息 SELECT TO_CHAR(BEGIN_TIME,'HH24:MI:SS') BEGIN_TIME, TO_CHAR(END_TIME,'HH24:MI:SS') END_TIME,UNDOBLKS FROM V$UNDOSTAT; 显示UNDO段统计信息 SELECT a.name, b.xacts, b.writes, b.extents FROM v$rollname a, v$rollstat b WHERE a.usn=b.usn; 显示活动事务信息 Col username format a10 Col name format a10 SELECT a.username, b.name, c.used_ublk FROM v$session a, v$rollname b, v$transaction c WHERE a.saddr=c.ses_addr AND b.usn=c.xidusn AND a.username='HR'; V$ROLLSTAT中的常用列 USN  Rollback segment number EXTENTS  Number of extents in the rollback segment RSSIZE  Size (in bytes) of the rollback segment. WRITES  Number of bytes written to the rollback segment XACTS  Number of active transactions GETS  Number of header gets WAITS  Number of header waits OPTSIZE  Optimal size of the rollback segment HWMSIZE  High-watermark of rollback segment size SHRINKS  Number of times the size of a rollback segment decreases WRAPS  Number of times rollback segment is wrapped EXTENDS  Number of times rollback segment size is extended AVESHRINK  Average shrink size AVEACTIVE  Current size of active extents, averaged over time. STATUS  Rollback segment status: ONLINE PENDING OFFLINE OFFLINE FULL CUREXT Current extent CURBLK Current block

5、读一致性
ORA-01555错误

6、undo advisor
EM




redo的中读一致性（ORA-01555错误机制问题）问题undo表空间的大小设置







解决这样问题：1. 确保undo表空间数据的保留时间至少大于最长sql语句的时间
      2. 增大undo表空间的大小
就是根据时间找大小。