启用SQL Server RDS慢日志收集功能（阈值设置为3秒），并运行几天后分析收集到的慢日志，对慢日志进行分类整理，找出执行频率高且耗时长的SQL进行分析。

--如下所示，执行的SQL并不复杂，只有一个主从表关联，但是总共执行了4870次，总耗时2650秒

declare @p1 int 

set @p1=180263033

declare @p3 int

set @p3=16

declare @p4 int

set @p4=1

declare @p5 int

set @p5=0

exec sp_cursoropen @p1 output,N'SELECT "T0"."FID" "ID", "T0"."FGROUPID" "T1.ID" FROM "T_HR_ATS_ATTENDANCELOGENTRY" "T0" INNER JOIN "T_HR_ATS_ATTENDANCELOG" "T1" ON "T0"."FGROUPID" = "T1"."FID" WHERE "T1"."FID" =  @P0  ORDER BY "T1.ID" ASC, "T0"."FSEQ" ASC',@p3 output,@p4 output,@p5 output,N'@P0 varchar(8000)','O9AAAACZJT4V4uUB'

select @p1, @p3, @p4, @p5

分析SQL的执行计划，存在明显的全表扫描（关联字段未加索引）：

Storage RowStore

Estimated Operator Cost 104.766 (99%)

Estimated I/O Cost 102.076

Estimated CPU Cost 2.69061

Estimated Subtree Cost 104.766

Estimated Number of Executions 1

Estimated Number of Rows to be Read 9.78391e+006

Estimated Number of Rows 1391.81

Estimated Row Size 45 B

给对应字段增加索引：

 CREATE NONCLUSTERED INDEX INDEX_ATTLOGENTRY_INDEX3 ON [dbo].[T_HR_ATS_AttendanceLogEntry] ([FGroupID])

重新查看执行计划，分析执行占比最大的节点执行情况，CPU Cost从2.69061

下降到了0.0032308，总耗时从2650秒下降到15秒：

Physical Operation Index Seek

Logical Operation Index Seek

Estimated Execution Mode Row

Storage RowStore

Estimated Operator Cost 0.0175073 (54%)

Estimated I/O Cost 0.0142766

Estimated CPU Cost 0.0032308

Estimated Subtree Cost 0.0175073

Estimated Number of Executions 1

Estimated Number of Rows to be Read 2794.34

Estimated Number of Rows 2794.34

Estimated Row Size 51 B