Oracle中IMU技术和redo private strand技术

oracle030

oracle030

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Oracle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。