Performance tweaks

SQLWATCHDB/dbo/ufn_time_intervals.sql

@@ -1,38 +1,41 @@
-CREATE FUNCTION [dbo].[ufn_time_intervals]
-(
-	@snapshot_type_id tinyint = null,
-	@interval_minutes smallint = 15,
-	@report_window int = 4,
-	@report_end_time datetime = '2099-12-31'
-)
-RETURNS TABLE
-AS RETURN (
-	select 
-			[spapshot_interval_start]
-		,	[snapshot_interval_end] = dateadd(mi, @interval_minutes, [spapshot_interval_start])
-		,	[first_snapshot_time]	= MIN(i.snapshot_time)
-		,	[last_snapshot_time]	= MAX(i.snapshot_time)
-		,	[snapshot_age_hours]	= datediff(hour,dateadd(mi, @interval_minutes, [spapshot_interval_start]),GETDATE())
-		,	[report_time_interval_minutes] = @interval_minutes
-		,	s.[snapshot_type_id]
-	from [dbo].[sql_perf_mon_snapshot_header] s
-	inner join (
-		select
-				[snapshot_time]
-			 ,	[spapshot_interval_start] = convert(datetime,dateadd(mi,(datediff(mi,0, [snapshot_time])/ @interval_minutes) * @interval_minutes,0))
-			 ,	[report_time_interval_minutes] = @interval_minutes
-			 ,	[snapshot_type_id]
-		from [dbo].[sql_perf_mon_snapshot_header]
-		where snapshot_type_id = isnull(@snapshot_type_id,snapshot_type_id)
-		and snapshot_time >= DATEADD(HOUR, -@report_window, @report_end_time)
-		and snapshot_time <= @report_end_time
-		) i
-		on s.snapshot_time > [spapshot_interval_start]
-		and s.snapshot_time <= dateadd(mi, @interval_minutes, [spapshot_interval_start])
-		and i.[snapshot_type_id] = s.[snapshot_type_id]
-	where s.snapshot_type_id = isnull(@snapshot_type_id,s.snapshot_type_id)
-	and dateadd(mi, @interval_minutes, i.[spapshot_interval_start]) > DATEADD(HOUR, -@report_window, @report_end_time)
-	and dateadd(mi, @interval_minutes, i.[spapshot_interval_start]) <= @report_end_time
-	group by [spapshot_interval_start], s.snapshot_type_id
-	)
-GO
+CREATE FUNCTION [dbo].[ufn_time_intervals]
+(
+	@snapshot_type_id tinyint = 1,
+	@interval_minutes smallint = null,
+	@report_window int = 4,
+	@report_end_time datetime = null
+)
+RETURNS TABLE
+AS RETURN (
+	/* if no @interval_minutes parameter specified we are going to 
+		pick best interval based on report window here */
+	with cte_interval_window as (
+		select interval_minutes = case when @interval_minutes is null then
+			case
+				when @report_window <= 1 then 2
+				when @report_window <= 4 then 5
+				when @report_window <= 24 then 15
+				when @report_window <= 168 then 60
+				when @report_window <= 720 then 360
+			else 1440 end
+		else @interval_minutes end
+	)
+		select
+				[first_snapshot_time]	= min([snapshot_time])
+			 ,  [last_snapshot_time]	= max([snapshot_time])
+			 ,	[spapshot_interval_start]	= convert(datetime,dateadd(mi,(datediff(mi,0, [snapshot_time])/ interval_minutes) * interval_minutes,0))
+			 ,	[snapshot_interval_end]		= dateadd(mi, interval_minutes, convert(datetime,dateadd(mi,(datediff(mi,0, [snapshot_time])/ interval_minutes) * interval_minutes,0)))
+			 ,	[report_time_interval_minutes] = interval_minutes
+			 ,	[snapshot_type_id]
+			 ,	[snapshot_age_hours]	= datediff(hour,dateadd(mi, interval_minutes, convert(datetime,dateadd(mi,(datediff(mi,0, [snapshot_time])/ interval_minutes) * interval_minutes,0))),getdate())
+		from [dbo].[sql_perf_mon_snapshot_header]
+		cross apply cte_interval_window
+		where snapshot_type_id = isnull(@snapshot_type_id,snapshot_type_id)
+		and snapshot_time >= DATEADD(HOUR, -@report_window, isnull(@report_end_time,getdate()))
+		and snapshot_time <= isnull(@report_end_time,getdate())
+		group by 
+				convert(datetime,dateadd(mi,(datediff(mi,0, [snapshot_time])/ interval_minutes) * interval_minutes,0))
+			,	dateadd(mi, interval_minutes, convert(datetime,dateadd(mi,(datediff(mi,0, [snapshot_time])/ interval_minutes) * interval_minutes,0)))
+			,	interval_minutes
+			,	[snapshot_type_id]
+)