CBO Cost Formulas成本計算公式大全: 成本模型：連接方式Join method 注意 連接基數(Join Cardinality)不受到連接方式(join method) 的影響， oracle中主要的三種join method HASH JOIN、Nested Loops、Sort Merge:

• Nested Loops嵌套循環成本公式：
  • Cost(outer)+Cost(inner))*cardinality(outer)
• Sort merge 合并排序連接成本公式:
  • Cost(outer) + Cost(inner) + Sort(outer) + Sort(inner)
• Hash Join 哈希連接公式:
  • Cost(outer) + Cost(inner) + Build(outer) + Probe(inner)

? Index Unique Scan Cost成本計算 INDEX UNIQUE SCAN COST = (BLEVEL (1-(OIC/100)) + 1) * (OICA/100) ? Index Range Scan Cost成本計算 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啟用的情況下： 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 +

轉載于:https://blog.51cto.com/maclean/1278512

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