Daily state aggregations appear to be stored against the wrong date in the data warehouse database when the time zone of the server hosting the SQL Server instance is at an offset to UTC. This is evident in the UK, because for approximately half the year the UK is on UTC, at which point the daily aggregations are stored against the correct date, but during BST (UTC+1) they are stored against the previous date. I suspect this may only affect time zones at a positive offset to UTC, and that the problem is in dbo.StandardDatasetAggregate, possibly related to the calculation of @IntervalStartDateTime, but I haven’t been able to pinpoint the bug. I also haven’t checked whether the same situation exists with the other aggregate types, such as performance.

The problem can be best illustrated with a script, which works against a database running in the UK for web application transaction monitor-data generated in 2014:

USE OperationsManagerDW

-- Determine a web application transaction monitor with relevant data, i.e. during BST and where an unhealthy state has been recorded.
DECLARE	@ManagedEntityMonitorRowId INT,
		@Date DATE

SELECT TOP 1
	@Date = sdf.[Date],
	@ManagedEntityMonitorRowId = sdf.ManagedEntityMonitorRowId
FROM
			dbo.vStateDailyFull sdf

INNER JOIN	dbo.vManagedEntity me
ON			sdf.ManagedEntityRowId = me.ManagedEntityRowId
AND			me.FullName LIKE 'WebApplication[_]%'
AND			me.FullName NOT LIKE '%WatcherComputersGroup'

WHERE
	sdf.MonitorRowId =	(
							SELECT TOP 1
								MonitorRowId
							FROM
								dbo.vMonitor
							WHERE
								MonitorSystemName = 'System.Health.EntityState'
						)
AND	(
			sdf.InYellowStateMilliSeconds > 10000
		OR	sdf.InRedStateMilliseconds > 10000
	)
AND	sdf.[Date] BETWEEN '31/Mar/2014' AND '25/Oct/2014'		-- ~BST.
ORDER BY
	sdf.[Date]

-- Return the data.
SELECT
	*
FROM
	dbo.vStateFull
WHERE
	ManagedEntityMonitorRowId = @ManagedEntityMonitorRowId
AND	[DateTime] >= @Date
AND	[DateTime] < DATEADD(d, 2, @Date)
ORDER BY
	[DateTime]

For a particular web application transaction monitor, my results for the daily aggregation (AggregationTypeId = 30) for 31/03/2014 show that InYellowStateMilliseconds is 206173, but the sum total of InYellowStateMilliseconds for the hourly aggregations (AggregationTypeId = 20) is 0 for this date. The figure of 206173 shows against the hourly aggregations associated with the following day, 01/04/2014.

I have logged this bug on Microsoft Connect.