CBO Cost Formulas基于成本优化器的成本计算公式大全

CBO Cost Formulas成本计算公式大全:

成本模型：连接方式Join method

注意 连接基数(Join Cardinality)不受到连接方式(join method) 的影响， oracle中主要的三种join method HASH JOIN、Nested Loops、Sort Merge:

Nested Loops嵌套循环成本公式：

Cost(outer)+Cost(inner))*cardinality(outer)

Sort merge 合并排序连接成本公式:

Cost(outer) + Cost(inner) + Sort(outer) + Sort(inner)

Hash Join 哈希连接公式:

Cost(outer) + Cost(inner) + Build(outer) + Probe(inner)

Index Unique Scan Cost成本计算
INDEX UNIQUE SCAN COST = (BLEVEL (1-(OIC/100)) + 1) * (OICA/100)

Index Range Scan Cost成本计算
INDEX RANGE SCAN COST = (BLEVEL + FF*LFBL)*(1-(OIC/100))+ FF*CLUF)* (OICA/100)

formula does not include the CPU cost

BLEVEL = number of branch levels in index

add +1 for leaf block

FF = filtering factor – selectivity

LFBL = number of leaf blocks

CLUF = index clustering factor

OIC = optimizer_index_caching(default 0)

OICA = optimizer_index_cost_adj parameter(default=100)

CPU costing启用的情况下：

mreadtime -Average time , in milliseconds, for a multi-block read (according to sys.aux_stats$)

sreadtime - Average time , in milliseconds, for a single-block read (according to sys.aux_stats$)

MBRC - Average number of blocks to be read in a multi-block read (according to sys.aux_stats$

#SRDs - number of single block reads

#MRDs - number of multi block reads

#CPUCycles - number of CPU Cycles

sreadtime = ioseektim + db_block_size/iotfrspeed

mreadtim = ioseektim + db_file_multiblock_read_count * db_block_size / iotrfspeed

#MRds = #Blks/MBRC

Cost 成本本身 =(#SRds * sreadtim +#MRds * mreadtim + #CPUCycles/cpuspeed)/sreadtim ,  

Cost成本的单位 为 single-block read time=sreadtim