Improve CTE performance

is there a way to improve the performance of a recursive CTE like below, I am unsure if I can add indexes on joins when the joins are using ROW_NUMBER?

DECLARE @File_Name VARCHAR(8000),
        @Disk VARCHAR(5)
SET @File_Name = 'MARSQLUTILITY,AdventureWorksDW_Data'
SET @Disk = 'I:'
--Code to pull out deltas between collected IO stats.
;WITH IOPS   ([IO_STALL]
           ,[IO_STALL_READ_MS]
           ,[IO_STALL_WRITE_MS]
           ,[NUM_OF_READS]
           ,[NUM_OF_WRITES]
           ,[SIZE_ON_DISK_MB]
           ,[DBNAME]
           ,[NAME]
           ,[FILE_ID]
           ,[DB_FILE_TYPE]
           ,[DISK]
           ,[FILE_LOCATION]
           ,[TIMESTAMP]
           ,[ROW])
AS
(
SELECT *, ROW_NUMBER() OVER (PARTITION BY FILE_LOCATION ORDER BY TIMESTAMP DESC) AS [ROW]
FROM dbo.DISKIOPS 
)

--Need to divide by the number of operations in that timeframe to get average wait time per operation.
--SELECT MAX(([IO2].[IO_STALL] - [IO1].[IO_STALL]) / (IO2.NUM_OF_READS + IO2.NUM_OF_WRITES - IO1.NUM_OF_READS - IO1.NUM_OF_WRITES))
SELECT [IO1].[TIMESTAMP],
       [IO1].[NAME],
      ([IO2].[IO_STALL] - [IO1].[IO_STALL]) / (IO2.NUM_OF_READS + IO2.NUM_OF_WRITES - IO1.NUM_OF_READS - IO1.NUM_OF_WRITES) AS Avg_Stall_Per_Operation
FROM IOPS IO1 JOIN IOPS IO2 ON IO1.ROW = (IO2.ROW+1)
WHERE IO1.NAME = IO2.NAME
--Need to make sure not dividing by 0 when there has been no operations
AND (IO2.NUM_OF_READS + IO2.NUM_OF_WRITES - IO1.NUM_OF_READS - IO1.NUM_OF_WRITES) > 0
AND IO1.Disk = @Disk

CTEs don't allow you to add indexes, they behave similarly to views but they aren't a persistent object in the database so they can't have indexes (unlike views).

If the bottle neck is the JOIN operation you should resort to a temp table and add an index on the column you will be using to speed up the JOIN operation.

StackExchange Database Administrators Q#46070, answer score: 3