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CBO之FullTableScan-FTS算法(二)

2015-07-24 10:44:33 · 作者: · 浏览: 8
标签: CBO FullTableScan-FTS 算法
----------------- ---------- CPUSPEEDNW 2894.14695 IOSEEKTIM 10 IOTFRSPEED 4096 SREADTIM MREADTIM CPUSPEED MBRC MAXTHR SLAVETHR

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（11）隐含参数： 
SQL> @?/rdbms/admin/show_para
Enter value for p: table_scan_cost
old  12:     AND upper(i.ksppinm) LIKE upper(‘%&p%‘)
new  12:     AND upper(i.ksppinm) LIKE upper(‘%table_scan_cost%‘)

P_NAME                                   P_DESCRIPTION                                      P_VALUE                          ISDEFAULT ISMODIFIED ISADJ
---------------------------------------- -------------------------------------------------- ------------------------------ --------- ---------- -----
_table_scan_cost_plus_one                bump estimated full table scan and index ffs cost  TRUE    TRUE      FALSE       FALSE
                                         by one

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（12）IO成本 
I/O Cost = 1 + CEIL(#MRds * (mreadtim / sreadtim))
/O Cost = 1 + CEIL(23.125 * ((10+16*8192/4096) / (10+8192/4096)))
SQL> select 1 + CEIL(23.125 * ((10+16*8192/4096) / (10+8192/4096))) from dual;

1+CEIL(23.125*((10+16*8192/4096)/(10+8192/4096)))
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(13)CPU成本 
CPU Cost = ROUND(#CPUCycles / cpuspeed / 1000 / sreadtim)
           ROUND(17634933/ 2894.14695 / 1000 / (10+8192/4096))=1

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