SqlCommand.ExecuteReader became very slow - sql-server

Question

I am using this code, to call an SQL function, which returns entries from an SQL Server database table
string cmd = String.Format("select * from dbo.GetData(#userId, #fileId, #created);");
using (SqlConnection conn = new SqlConnection(connectionString))
{
if (conn.State != ConnectionState.Open)
conn.Open();
SqlCommand command = new SqlCommand(cmd, conn);
if (String.IsNullOrEmpty(userId))
command.Parameters.AddWithValue("#userId", DBNull.Value);
else
command.Parameters.AddWithValue("#userId", userId);
if (String.IsNullOrEmpty(fileId))
command.Parameters.AddWithValue("#fileId", DBNull.Value);
else
command.Parameters.AddWithValue("#fileId", docId);
command.Parameters.AddWithValue("#created", created);
internalWatch.Reset();
internalWatch.Start();
IDataReader reader = command.ExecuteReader();
table = GetDataTableFromDataReader(reader);
reader.Close();
reader.Dispose();
conn.Close();
internalWatch.Stop();
The table I am working with contains a bit more than 1.5 million entries and should return a bit more than 250k entries.
If I am executing the SQL function within SSMS it needs 8 seconds to return the results and I already used the code above last week to get the results within my desktop application. At this time everything was fine. The code needed between 10-12 seconds to get the results.
The strange thing is, that today the code needs more than 40 seconds to return the same results, but I haven't change anything within the SQL function or the code itself. The only change I did in my programm is adding a few more classes, which have nothing to do with the code above.
If I am debugging the code, I can see, that the line
IDataReader reader = command.ExecuteReader();
needs the most of the time now.
Since I haven't change anything in the SQL function or the code itself, I can't understand why it is taking so long now...
And if needed, here is the SQL function, I am using:
ALTER FUNCTION [dbo].[GetData]
(#userId varchar(128) = NULL,
#fileId varchar(192) = NULL,
#created DateTimeOffset(7))
RETURNS TABLE
AS
RETURN (
WITH FindNewestVersion AS
(
SELECT
*,
ROW_NUMBER() OVER (PARTITINO BY FileId, UserId
ORDER BY created DESC) rn
FROM
table1
)
SELECT
q.Created, q.Updated, q.FileId, q.UserId,
F.column1, F.column2, F.column3
FROM
table2 AS F
INNER JOIN
table1 AS q ON F.column4 = q.PersonId AND F.created = q.created
INNER JOIN
(SELECT
created, PersonId, DocumentId
FROM
FindNewestVersion
WHERE
rn = 1) AS x ON q.created = x.created
AND q.PersonId = x.PersonId
AND q.FileId = x.FileId
WHERE
(F.column1 = 'Sample')
AND (q.Created <= #created)
AND (q.Updated >= #created)
AND Q.PersonId = ISNULL(#userId, Q.PersonId)
AND Q.FileId = ISNULL(#fileId, Q.FileId)
)
Thank you for any suggestions!

Answer 1

This seems like a case of parameter sniffing
One thing that you could do is rewrite your procedure as follows:
`
DROP FUNCTION [dbo].[GetData]
CREATE PROCEDURE[dbo].[GetData]
(
#userId varchar(128) = NULL,
#fileId varchar(192) = NULL,
#created DateTimeOffset(7)
)
RETURNS TABLE
AS
DECLARE #l_userId varchar(128) = NULL,
DECLARE #l_fileId varchar(192) = NULL,
DECLARE #l_created DateTimeOffset(7)
SET #l_userId = userId
SET #l_fileId = fileId
SET #l_created = #created
(
WITH FindNewestVersion as
(
Select *, ROW_NUMBER()
over (partition by FileId, UserId ORDER BY created DESC)rn from table1
)
SELECT q.Created, q.Updated, q.FileId, q.UserId,
F.column1, F.column2, F.column3
FROM table2 AS F INNER JOIN
table1 AS q
ON F.column4 = q.PersonId AND F.created = q.created
INNER JOIN
(
select created, PersonId, DocumentId from FindNewestVersion where rn = 1
) AS x ON q.created = x.created AND q.PersonId = x.PersonId AND q.FileId = x.FileId
WHERE (F.column1 = 'Sample') AND (q.Created <= #created) AND (q.Updated >= #created)
And Q.PersonId = ISNULL(#l_userId, Q.PersonId)
And Q.FileId = ISNULL(#l_fileId, Q.FileId)
)
`
You can then get you data as you would by calling a stored procedure.

Answer 2

This seems like a case of SET ARITHABORT ON
By default in SQL it's On But while we execute Through C# Code then its not understand the ARITHABORT ON.
One thing that you could do is rewrite your procedure as follows:
DROP FUNCTION [dbo].[GetData]
CREATE PROCEDURE[dbo].[GetData]
(
#userId varchar(128) = NULL,
#fileId varchar(192) = NULL,
#created DateTimeOffset(7)
)
RETURNS TABLE
AS
SET ARITHABORT ON
DECLARE #l_userId varchar(128) = NULL,
DECLARE #l_fileId varchar(192) = NULL,
DECLARE #l_created DateTimeOffset(7)
SET #l_userId = userId
SET #l_fileId = fileId
SET #l_created = #created
(
WITH FindNewestVersion as
(
Select *, ROW_NUMBER()
over (partition by FileId, UserId ORDER BY created DESC)rn from table1
)
SELECT q.Created, q.Updated, q.FileId, q.UserId,
F.column1, F.column2, F.column3
FROM table2 AS F INNER JOIN
table1 AS q
ON F.column4 = q.PersonId AND F.created = q.created
INNER JOIN
(
select created, PersonId, DocumentId from FindNewestVersion where rn = 1
) AS x ON q.created = x.created AND q.PersonId = x.PersonId AND q.FileId = x.FileId
WHERE (F.column1 = 'Sample') AND (q.Created <= #created) AND (q.Updated >= #created)
And Q.PersonId = ISNULL(#l_userId, Q.PersonId)
And Q.FileId = ISNULL(#l_fileId, Q.FileId)
)`enter code here`