How to determine if you should use full or differential backup?
- by Peter Larsson
Or ask yourself, "How much of the database has changed since last backup?".
Here is a simple script that will tell you how much (in percent) have changed in the database since last backup.
-- Prepare staging table for all DBCC outputs
DECLARE @Sample TABLE
(
Col1 VARCHAR(MAX) NOT NULL,
Col2 VARCHAR(MAX) NOT NULL,
Col3 VARCHAR(MAX) NOT NULL,
Col4 VARCHAR(MAX) NOT NULL,
Col5 VARCHAR(MAX)
)
-- Some intermediate variables for controlling loop
DECLARE @FileNum BIGINT = 1,
@PageNum BIGINT = 6,
@SQL VARCHAR(100),
@Error INT,
@DatabaseName SYSNAME = 'Yoda'
-- Loop all files to the very end
WHILE 1 = 1
BEGIN
BEGIN TRY
-- Build the SQL string to execute
SET @SQL = 'DBCC PAGE(' + QUOTENAME(@DatabaseName) + ', ' + CAST(@FileNum AS VARCHAR(50)) + ', '
+ CAST(@PageNum AS VARCHAR(50)) + ', 3) WITH TABLERESULTS'
-- Insert the DBCC output in the staging table
INSERT @Sample
(
Col1,
Col2,
Col3,
Col4
)
EXEC (@SQL)
-- DCM pages exists at an interval
SET @PageNum += 511232
END TRY
BEGIN CATCH
-- If error and first DCM page does not exist, all files are read
IF @PageNum = 6
BREAK
ELSE
-- If no more DCM, increase filenum and start over
SELECT @FileNum += 1,
@PageNum = 6
END CATCH
END
-- Delete all records not related to diff information
DELETE
FROM @Sample
WHERE Col1 NOT LIKE 'DIFF%'
-- Split the range
UPDATE @Sample
SET Col5 = PARSENAME(REPLACE(Col3, ' - ', '.'), 1),
Col3 = PARSENAME(REPLACE(Col3, ' - ', '.'), 2)
-- Remove last paranthesis
UPDATE @Sample
SET Col3 = RTRIM(REPLACE(Col3, ')', '')),
Col5 = RTRIM(REPLACE(Col5, ')', ''))
-- Remove initial information about filenum
UPDATE @Sample
SET Col3 = SUBSTRING(Col3, CHARINDEX(':', Col3) + 1, 8000),
Col5 = SUBSTRING(Col5, CHARINDEX(':', Col5) + 1, 8000)
-- Prepare data outtake
;WITH cteSource(Changed, [PageCount])
AS (
SELECT Changed,
SUM(COALESCE(ToPage, FromPage) - FromPage + 1) AS [PageCount]
FROM (
SELECT CAST(Col3 AS INT) AS FromPage,
CAST(NULLIF(Col5, '') AS INT) AS ToPage,
LTRIM(Col4) AS Changed
FROM @Sample
) AS d
GROUP BY Changed
WITH ROLLUP
)
-- Present the final result
SELECT COALESCE(Changed, 'TOTAL PAGES') AS Changed,
[PageCount],
100.E * [PageCount] / SUM(CASE WHEN Changed IS NULL THEN 0 ELSE [PageCount] END) OVER () AS Percentage
FROM cteSource
