"sp_spaceused" returns not uptodate numbers - sql-server-express

Question

We use "sp_spaceused" in a while-loop where we delete data.
We do so in order to remain under the 10GB SQL Express Edition limit.
The Delete routine that runs nightly
PROCEDURE [dbo].[DeletePeriod4Data]
#LIMIT_InMB AS FLOAT
AS
BEGIN
SET NOCOUNT ON
DECLARE #MinBegin AS DATETIME
DECLARE #SizePeriod4_InMB AS FLOAT
EXEC [dbo].[GetDatabaseStatsPeriod4MB]
#Size_InMB = #SizePeriod4_InMB OUTPUT
WHILE #SizePeriod4_InMB > #LIMIT_InMB
BEGIN
SELECT #MinBegin = MIN(MONTH.ProdData.[Begin])
FROM MONTH.ProdData
PRINT 'deleting from period 4, month and year of: '
PRINT #MinBegin
DELETE
FROM Month.ProdData
WHERE
Year = DATEPART(YEAR, #MinBegin)
AND
Month = DATEPART(MONTH, #MinBegin)
EXEC [GetDatabaseStatsPeriod4MB]
#Size_InMB = #SizePeriod4_InMB OUTPUT
END
END
And this is the culprit stored procedure that returns outofdate numbers.
PROCEDURE [dbo].[GetDatabaseStatsPeriod4MB]
#Size_InMB float OUTPUT
AS
BEGIN
CREATE TABLE #t (name SYSNAME, rows CHAR(11), reserved VARCHAR(18),
data VARCHAR(18), index_size VARCHAR(18), unused VARCHAR(18))
DBCC UPDATEUSAGE(0); -- <-- helps?
EXEC sp_msforeachtable #command1=
'INSERT INTO #t EXEC sp_spaceused ''?'', #updateUsage=''TRUE''',
#whereand=' and schema_name(schema_id) = ''Month'' '
SELECT #Size_InMB =
SUM(CONVERT(INT, SUBSTRING(data, 1, LEN(data)-3)))/1024.0
FROM #t
DROP TABLE #t
PRINT 'PERIODE 4 Size (Month)'
PRINT #Size_InMB
END
What we tried is
Adding parameter "#updateUsage=TRUE" to sp_spaceused
Added call to "DBCC UPDATEUSAGE(0);"
Added params to "DBCC UPDATEUSAGE(0) WITH NO_INFOMSGS, COUNT_ROWS;"
Using a delay before I call “UpdateUsage”
WAITFOR DELAY '00:00:05' ---- 5 Second Delay
Generic code to repro the problem
CREATE TABLE #t (name SYSNAME, rows CHAR(11), reserved VARCHAR(18),
data VARCHAR(18), index_size VARCHAR(18), unused VARCHAR(18))
EXEC sp_msforeachtable #command1=
'INSERT INTO #t EXEC sp_spaceused ''?'', #updateUsage=''TRUE'''
SELECT SUM(CONVERT(INT, SUBSTRING(data, 1, LEN(data)-3)))/1024.0
FROM #t
DROP TABLE #t
-- Delete something in your DB (Northwind)
-- Run the above again

Answer 1

You need to allow for time for Ghost Cleanup to handle the ghosted records since DELETE doesn't actually delete anything, it just marks the records as ghosted in the slot on the page and then it is the job of the Ghost Cleanup task to clean those up later. You can read about this in Paul's blog posts:
Inside the Storage Engine - Ghost Cleanup in Depth
Ghost Cleanup - Redux
Truning off the Ghost Cleanup Task for a Performance Gain
You can also track Ghost Cleanup activity with Extended Events in SQL Server 2008+ as I show in my blog post:
Tracking Ghost Cleanup
You either need to wait between the delete and checking for space used to allow Ghost Cleanup to run or between the delete and the check for space used, force Ghost Cleanup by forcing an index scan as Paul explains in his blog posts.