Question

我正在尝试调整查询，我的解释计划中的所有内容都具有非常低的成本。我正在使用物化视图和适当的指数，但计划的最终成本是239,925，其他一切都在0-69之间。我错过了什么？我已经分区了大型mvs，并行性和索引。

对图片感到抱歉，但我不确定导出解释计划的其他方法。

代码如下所示：

       UPDATE KC_TEST_REPORT_2 rep 
        SET    (    department, 
                    documenttype, 
                    orgfunction, 
                    risklevel, 
                    assetcriticality, 
                    cft 
                ) = ( 
        SELECT
                    dept.valstr Department, 
                    doctype.valstr DocumentType, 
                    orgFunc.valstr OrgFunction, 
                    risk.valstr    RiskLevel, 
                    crit.valstr    AssetCriticality, 
                    cft.valstr     CFT 
        FROM   MV_LLATTRDATA_SHRUNK_V3 dept 
                left outer join MV_LLATTRDATA_SHRUNK_V3 doctype 
                            ON doctype.defid = 3070055 
                            AND doctype.attrid = 6 
                            AND doctype.vernum = dept.vernum 
                            AND  doctype.defvern = dept.defvern 

                left outer join MV_LLATTRDATA_SHRUNK_V3 orgFunc 
                            ON orgFunc.defid = 3070055 
                            AND orgFunc.attrid = 2 
                            AND orgFunc.vernum = dept.vernum 
                            AND orgFunc.defvern = dept.defvern 

                left outer join MV_LLATTRDATA_SHRUNK_V3 risk 
                            on risk.defid=3070055 
                            and risk.attrid = 20 
                            AND risk.vernum = dept.vernum 
                            AND risk.defvern = dept.defvern 

                left outer join MV_LLATTRDATA_SHRUNK_V3 crit 
                            ON crit.defid = 3070055 
                            AND crit.attrid = 24 
                            AND crit.vernum = dept.vernum 
                            AND crit.defvern = dept.defvern 

                left outer join MV_LLATTRDATA_SHRUNK_V3 cft 
                            ON cft.defid = 3070055 
                            AND cft.attrid = 23 
                            AND cft.vernum = dept.vernum 
                            AND cft.defvern = dept.defvern 

        WHERE  dept.id = rep.dataid 
                AND dept.defid = 3070055 
                AND dept.attrid = 4 
                AND doctype.id = rep.dataid 
                AND orgFunc.id = rep.dataid 
                AND orgFunc.entrynum = 1 
                AND risk.id = rep.dataid 
                AND crit.id = rep.dataid 
                AND cft.id = rep.dataid 
                AND dept.vernum =  (SELECT MV.vernum
                                    FROM   MV_LLATTRBLOBDATA_VERNNUM_V1 MV 
                                    WHERE  id = rep.dataid) 
                AND dept.defvern = (SELECT MV.MAX_DEFVERN
                                    FROM   MV_LLATTRDATA_MAX_VERSIONS_V1 MV
                                    WHERE id = rep.dataid 
                                        AND defid = 3070055 
                                        AND attrid = 4));

Answer 1

This is not the correct way to tune a query. The cost column is not a measurement of the cost of your query. It's used internally to compare between the many different plans the optimizer came up with to make its decision as to which one is best.

Instead, what you should be doing is looking at an execution plan, at the actual time for each step, the estimated rows vs. the actual rows, and maybe seeing if there are some missing indexes or something.

You might want to refer to the Database Performance Tuning Guide.

解释计划最终成本与每个步骤的成本不匹配

1 个答案: