了避免DBWR不必要的唤醒及过于活跃,从Oracle10g开始,Oracle对DBWR的SCAN间隔进行了调整.
在内部由一个隐含参数:_dbwr_scan_interval 控制.

Oracle9i中这个参数缺省值为10 s:

SQL> select * from v$version  2  /
BANNER----------------------------------------------------------------Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit ProductionPL/SQL Release 9.2.0.4.0 - ProductionCORE    9.2.0.3.0       ProductionTNS for Solaris: Version 9.2.0.4.0 - ProductionNLSRTL Version 9.2.0.4.0 - Production
SQL> col ksppinm for a20SQL> col ksppdesc for a40SQL> col ksppstvl for a10SQL> select  2    ksppinm,ksppdesc,ksppstvl  3  from  4    sys.x$ksppi x,  5    sys.x$ksppcv y  6  where  7    x.inst_id = userenv('Instance') and  8    y.inst_id = userenv('Instance') and  9    x.indx = y.indx and 10    x.ksppinm like '%_dbwr_scan%' 11  /
KSPPINM              KSPPDESC                                 KSPPSTVL-------------------- ---------------------------------------- ----------_dbwr_scan_interval  dbwriter scan interval                   10
 

从Oracle10g开始,此缺省值被调这个为300 s:

SQL> select * from v$version  2  /
BANNER----------------------------------------------------------------Oracle Database 10g Enterprise Edition Release 10.1.0.3.0 - 64biPL/SQL Release 10.1.0.3.0 - ProductionCORE    10.1.0.3.0      ProductionTNS for Solaris: Version 10.1.0.3.0 - ProductionNLSRTL Version 10.1.0.3.0 - Production
SQL> col ksppinm for a20SQL> col ksppdesc for a40SQL> col ksppstvl for a10SQL> select  2    ksppinm,ksppdesc,ksppstvl  3  from  4    sys.x$ksppi x,  5    sys.x$ksppcv y  6  where  7    x.inst_id = userenv('Instance') and  8    y.inst_id = userenv('Instance') and  9    x.indx = y.indx and 10    x.ksppinm like '%_dbwr_scan%' 11  /
KSPPINM              KSPPDESC                                 KSPPSTVL-------------------- ---------------------------------------- ----------_dbwr_scan_interval  dbwriter scan interval                   300
 

在Oracle10gR2中,这个参数未作进一步调整,缺省值仍然为300:

SQL> select * from v$version  2  /
BANNER----------------------------------------------------------------Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - ProdPL/SQL Release 10.2.0.1.0 - ProductionCORE    10.2.0.1.0      ProductionTNS for Linux: Version 10.2.0.1.0 - ProductionNLSRTL Version 10.2.0.1.0 - Production
SQL> col ksppinm for a20SQL> col ksppdesc for a40SQL> col ksppstvl for a10SQL> select  2    ksppinm,ksppdesc,ksppstvl  3  from  4    sys.x$ksppi x,  5    sys.x$ksppcv y  6  where  7    x.inst_id = userenv('Instance') and  8    y.inst_id = userenv('Instance') and  9    x.indx = y.indx and 10    x.ksppinm like '%_dbwr_scan%' 11  /
KSPPINM              KSPPDESC                                 KSPPSTVL-------------------- ---------------------------------------- ----------_dbwr_scan_interval  dbwriter scan interval                   300
 

以上内容,仅供参考.