Understanding execution plans using TVPs

Question

I have some slow running queries (8 seconds across 1M records grouped by months) and have been trying to make sense of the execution plans. We use around 10 TVPs to send in a set of filters that the user chooses and I have an indexed view that accounts for 84% of the cost of the query.

The execution plan is pretty large and can't be uploaded here due to the size so I have uploaded it to here

I've spent quite a lot of time trying to optimise these queries (there are 14 of them but the core of each is much the same) and would appreciate anyone's suggestions or hints in reading them. I have also implemented the query suggested by the actual execution plan and the query was 5 times slower?

Answer 1

I don't think this query is about TVPs so much as complexity. The plan has an optimizer timeout. You can see it in the F4 properties of the SELECT operator as "Reason for Early Termination of Statement = Time Out" or StatementOptmEarlyAbortReason="TimeOut" in the plan xml. These are not always a disaster, it just means the optimizer has run out of time (more iterations) to come up with a plan and picks the lowest cost one it has at that stage. Optimizer timeouts are often a sign of over-complexity in a query and the common recommendation is to simplify, eg break it up, remove unnecessary parameters and joins etc

Looking at your query, there are 13 tables. Looking in the plan, many of them just do a "SELECT all records" from the lookup table ( eg all records from dbo.Station for the @from and @to tables, all ticketFilter and ticketClass records ), so actually you don't need these tables and removing them does not change the result. I understand this is a user-driven query, so you might look at approach where you only join to the tables if the user has actually applied a filter.

I can reproduce the timeout, and remove it by commenting out 4 of the tables, eg:

SELECT d.Month_Year[PeriodName], qg.Title [Service_Area], AVG((CAST(sa.Answer AS smallmoney) * 10.00)) [Average]
FROM [dbo].StaticDataView d WITH (NOEXPAND)
    INNER JOIN [dbo].[Survey] s  ON (s.CustomerJourney = d.Journey_Id)
        INNER JOIN [dbo].[SurveyAnswer] sa   ON (sa.Survey = s.ID)
            INNER JOIN [dbo].[Question] q  ON (q.ID = sa.Question)
                INNER JOIN [dbo].[QuestionGroup] qg  ON (qg.ID = q.QuestionGroupID)

    --INNER JOIN @StationFrom sfl ON (sfl.ID = d.[Source])
    --INNER JOIN @StationTo stl ON (stl.ID = d.[Dest])
    INNER JOIN @InitialScores sc ON (s.Score = sc.ID)
    INNER JOIN @RouteList rl ON (rl.ID = d.Route_ID) -- route list
    --INNER JOIN @TicketClass tc ON (tc.ID = d.Class_ID)
    --INNER JOIN @TicketTypeFilter ttl ON (ttl.ID = d.Ticket_Filter_Type_ID)
    INNER JOIN @TicketDiscount td ON (td.ID = d.Discount_Type_ID)
    INNER JOIN @Days dy ON (dy.ID = d.[DayOfWeek])

WHERE s.DateCompleted IS NOT NULL AND sa.Answer != -1
AND (d.RSID = COALESCE(@RSID, d.RSID))
AND (d.[Date] BETWEEN @Start AND @End) -- between dates
AND (d.[Time] BETWEEN @StartTime AND @EndTime) -- between times
AND ((@Direction IS NULL AND d.Direction IN (0,1)) -- Both
        OR (@Direction = 1 AND d.Direction = 1) -- North
        OR (@Direction = 0 AND d.Direction = 0)) -- South
AND ((@PassengerJourney = 0 AND d.Journey_Type_ID IN (1,2,3)) -- ALL
    OR (@PassengerJourney IN (1,2) AND @PassengerJourney = d.Journey_Type_ID) -- Single or Return
    OR (@PassengerJourney = 3 AND NULLIF(d.RSID_LEG_2,'') IS NOT NULL)) -- multi part
GROUP BY d.Month_Year, qg.Title
OPTION ( RECOMPILE )

Does this make for a better plan? Hard to say, as in my simple rig, I can't get this query to run in more than half a second, with or without the timeout. Even SQLFiddle doesn't seem to struggle. Can you see much difference between the SQLFiddle repro and your setup?