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$ksppcv y; 6; where; 7;x.inst_id = userenv('Instance') and; 8;y.inst_id = userenv('Instance') and; 9;x.indx = y.indx and 10;x.ksppinm like '%_dbwr_scan%' 11; /
KSPPINM;;;KSPPDESC KSPPSTVL-------------------- ---------------------------------------- ----------_dbwr_scan_interval; dbwriter scan interval10
从Oracle10g开始,此缺省值被调这个为300 s: SQL> select * from v$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 interval300

; 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 interval300
以上内容,仅供参考.