SQL Server 2014 sporadic poor query performance

Question

We have sporadic poor query performance of the same query with just a different parameter and we do not know why this is happening.

Maybe someone has an idea how this can happen.

We are running the same query thousands of times a day and somehow a few times the query runs 400ms instead of 1ms.

I created a trace-file to get some information which exact query is causing the problems and found this in the trace log:

exec sp_executesql 
           N'SELECT A.* 
             FROM Teile A 
             WHERE (A.Barcode = @P1)  
             ORDER BY A.Barcode ASC, A.ID ASC 
             OFFSET 0 ROWS FETCH FIRST 1 ROWS ONLY', 
           N'@P1 char(26)','1022669459                '

This query starts at 15:24:03.250 and stops at 15:24:03.650 => duration 400ms.

During the execution the query

exec sp_executesql 
           N'SELECT A.* 
             FROM Teile A 
             WHERE (A.Barcode = @P1)  
             ORDER BY A.Barcode ASC, A.ID ASC 
             OFFSET 0 ROWS FETCH FIRST 1 ROWS ONLY', 
           N'@P1 char(26)','1015092284                '

starts at 15:24:03.450 and stops at 15:24:03.451 => duration 1ms.

Has anybody an idea why the same query with just a different parameter is executing very slow and another as the average in 1ms?

I tried the first query in the smss but there I always get a execution time of 1ms, too. So it seems to me the server sometimes needs more time to execute the query, but I do not know why and have no idea to found out why.

Every help is greatly appreciated.

Thanks, Markus

Answer 1

Seems like parameter sniffing or bad statistics.
Try following:
1.Update statistics for the table
2.Add "OPTION (RECOMPILE)" to the end of the query
3.Add "OPTION (OPTIMIZE for UNKNOWN)" to the end of the query