Tanks for your useful explanation.

As you mentioned and if I understood correctly,if there is a shared table-lock , the INSERT would be blocked until the whole operation(select) completed .Is there any recognizable reason for the shared table-lock?

In a select statement i use WITH (HOLDLOCK) to see the locks.

BEGIN TRANSACTION

SELECT COUNT(*) AS [Count],

[t1].[h] AS [Hour],

[t1].[Transk] AS [Kind]

FROM (

SELECT DATEPART(Hour, [t0].[Date]) AS [h],

[t0].[Transk]

FROM [dbo].[Trans] AS [t0] WITH (HOLDLOCK)

WHERE ([t0].[Success] = 1)

AND ([t0].[Type] = 1)

AND ([t0].[Date] >= '2012-11-05 00:00:00')

AND ([t0].[Date] < '2012-11-06 00:00:00')

) AS [t1]

GROUP BY

[t1].[h],

[t1].[Transk]

SELECT resource_type, request_mode, resource_description

FROM sys.dm_tran_locks

WHERE resource_type <> 'DATABASE'

COMMIT

and this is the output:

resource_typerequest_moderesource_description

OBJECT S

hence ,the INSERT would be blocked?how can i avoid this problem?

I suppose the time out that I have in Inserts is because of this,am i true?

in this case I even check indexes but they are properly created and there isn't any unused index.

How can i monitor these time out a part from SQL Profiler(because of low performance) to see the locks either in the past(i mean a history) or at the moment?