[20130318]v$rman_backup_job_details访问缓慢的问题.txt

今天我想检查备份,执行如下:

SELECT start_time, end_time, elapsed_seconds,TRIM (time_taken_display) TIME, status, input_type,

       compression_ratio, TRIM (input_bytes_display) inputb,

       TRIM (output_bytes_display) outputb,

       TRIM (input_bytes_per_sec_display) input,

       TRIM (output_bytes_per_sec_display) output,

       status

  FROM v$rman_backup_job_details

 WHERE start_time > TRUNC (SYSDATE) - 22

 order by start_time desc ;

--我生产系统的版本信息如下:

select * from v$version where rownum<=1;

BANNER                                                          

----------------------------------------------------------------

Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

1 row selected.

--系统如死机一般,根本不动.
--仔细看执行计划,发现有好几个地方使用笛卡尔集MERGE JOIN CARTESIAN.
--我马上想起来,上个星期5我执行分析收集fixed table信息。
exec dbms_stats.gather_fixed_objects_stats;

--马上修改sql语句,加入提示rule 看看.

SELECT   /*+ rule */

         start_time, end_time, elapsed_seconds, TRIM (time_taken_display) TIME, status, input_type, compression_ratio,

         TRIM (input_bytes_display) inputb, TRIM (output_bytes_display) outputb, TRIM (input_bytes_per_sec_display) input,

         TRIM (output_bytes_per_sec_display) output, status

    FROM v$rman_backup_job_details

   WHERE start_time > TRUNC (SYSDATE) - 32

ORDER BY start_time DESC;

--结果马上返回.google发现如下链接:

http://rupamverma.blogspot.com/2010/11/oracle-database-backup-report.html
Oracle Database Backup Report - v$rman_backup_job_details

/*
-- rman - Query using V$RMAN_BACKUP_JOB_DETAILS is taking too long to execute both in SQL*Plus and also in DATABASE CONSOLE.
-- doc : 420200.1
*/
Steps :-
1. sqlplus as sysdba
2. execute following procedure

Sql> exec dbms_stats.DELETE_TABLE_STATS('SYS','X$KCCRSR'); # deletes the statistics on the fixed object.
Sql> exec dbms_stats.LOCK_TABLE_STATS('SYS','X$KCCRSR');   # lock that object so that statistics will not be collected in future.
 
Hope this helps. Regards Rupam

--按照建议就是删除SYS.X$KCCRSR上的统计,lock统计.

SELECT obj#, savtime, flags, rowcnt, blkcnt, avgrln, samplesize, analyzetime

  FROM SYS.wri$_optstat_tab_history

 WHERE obj# IN (SELECT object_id FROM v$fixed_table WHERE NAME = 'X$KCCRSR');

      OBJ# SAVTIME                          FLAGS     ROWCNT     BLKCNT     AVGRLN SAMPLESIZE ANALYZETIME

---------- --------------------------- ---------- ---------- ---------- ---------- ---------- -------------------

4294952064 2013-03-15 15:21:48.724980           8    5456             0        144       5456 2012-03-07 08:12:52

--不知道以前分析,问题为什么不出现.

SQL> select * from DBA_TAB_STATS_HISTORY where table_name='X$KCCRSR';

OWNER  TABLE_NAME  PARTITION_NAME                 SUBPARTITION_NAME              STATS_UPDATE_TIME

------ ----------- ------------------------------ ------------------------------ ----------------------------------------

SYS    X$KCCRSR                                                                   2013-03-15 15:21:48.724980

--这种fixed表不保留原来的统计信息.

解决方法两个:
1.使用提示rule.
2.删除统计信息,在lock统计.
exec dbms_stats.DELETE_TABLE_STATS('SYS','X$KCCRSR');
exec dbms_stats.LOCK_TABLE_STATS('SYS','X$KCCRSR');