Transaction Log Will Not Truncate

,

I saw a posting recently of a DBA not being able to truncate a transaction log. I rememberred this script that I had, (downloaded from Microsoft Support many moons ago), which did the job for me. It basically filled the log with data, then truncated and shrank the log. All important points throughout the script are commented.

/*
Shrink a named transaction log file belonging to a database

Originally found at;

http://support.microsoft.com/support/kb/articles/q256/6/50.asp

Changes:
28.08.2001
Modified the inner loop so it tested the dx time so long overruns did not happen
Modified the inner loop so it had a fixed minimum quantity so there was no skip in skip out

29.08.2001
Modified the inner loop so it had a dynamic minimum quantity to allow faster shrinkage

24.01.2002
Modified the USE statement so it uses brackets around the dbname
Modified the @TruncLog variable so it uses brackets around the dbname

31.05.2002
Modified the code to use PRINT instead of SELECT in several cases
Modified the code to use @MaxCount instead of two unclear rules 
Modified the code to use @Factor instead of several hard-coded values 
Commented the use of @Factor
Moved the configuration and @Counter init code to before the start of the first loop to avoid repetition
Modified the code to display the process runtime in seconds rather than minutes

*/

SET NOCOUNT ON

DECLARE @LogicalFileName SYSNAME,
        @MaxMinutes INT,
        @NewSize INT,
        @Factor FLOAT

/*
  The process has several control parameters, most of the time you only need to worry about the first four
    as these are the big controls whereas the fifth is simply a fine tuning control which rarely needs to 
    come into play.
*/

--This is the name of the database for which the log will be shrunk.
USE [Speqs]

--Use sp_helpfile to identify the logical file name that you want to shrink.
SET @LogicalFileName = 'Speqs_Log';
--Limit on time allowed to wrap log in minutes
SET @MaxMinutes = 5;
--Ideal size of logfile in MB
SET @NewSize =100;

/*
  Factor determining maximum number of pages to pad out based on the original number of pages in use 
    (single page = 8K).  Values in the range 1.0 - 0.8 seems to work well for many databases.

  Increasing the number will increase the maximum number of pages allowed to be padded, which should
    force larger amounts of data to be dropped before the process finishes.  Often speeds up shrinking
    very large databases which are going through the process before the timer runs out.

  Decreasing the number will decrease the maximum number of pages allowed to be padded, which should
    force less work to be done.  Often aids with forcing smaller databases to shrink to minimum size
    when larger values were actually expanding them.

*/
SET @Factor = 1.0;                        

/*
  All code after this point is driven by these parameters and will not require editing unless you need to 
    fix a bug in the padding/shrinking process itself.
*/

-- Setup / initialize
DECLARE @OriginalSize INT,
        @StringData VARCHAR(500)

SELECT @OriginalSize = size -- in 8K pages
FROM sysfiles
WHERE name = @LogicalFileName;

SELECT @StringData = 'Original Size of ' + db_name() + ' LOG is ' + 
    CONVERT(VARCHAR(30),@OriginalSize) + ' 8K pages or ' + 
    CONVERT(VARCHAR(30),(@OriginalSize*8/1024)) + 'MB'
FROM sysfiles
WHERE name = @LogicalFileName;

PRINT @StringData;
PRINT ''

--Drop the temporary table if it already exists
IF ( OBJECT_ID('[dbo].[DummyTrans]') IS NOT NULL )
  DROP TABLE [DummyTrans]

CREATE TABLE [DummyTrans]( [DummyColumn] CHAR(8000) NOT NULL );

-- Wrap log and truncate it.
DECLARE @Counter   INT,
        @MaxCount  INT,
        @StartTime DATETIME,
        @TruncLog  VARCHAR(500)

-- Try an initial shrink.
DBCC SHRINKFILE (@LogicalFileName, @NewSize)

SET @TruncLog = 'BACKUP LOG [' + db_name() + '] WITH TRUNCATE_ONLY';
EXEC (@TruncLog)

-- Configure limiter
IF @OriginalSize / @Factor > 50000
    SET @MaxCount = 50000
ELSE
    SET @MaxCount = @OriginalSize * @Factor

-- Attempt to shrink down the log file
PRINT 'Minimum Quantity : '+CAST( @MaxCount AS VARCHAR(10) )
PRINT 'Maximum Time : '+CAST( @MaxMinutes AS VARCHAR(10) )+' minutes ('+CAST( @MaxMinutes*60 AS VARCHAR(10) )+' seconds)'
PRINT ''

SET @Counter = 0;
SET @StartTime = GETDATE();

--loop the padding code to reduce the log while
-- within time limit and 
-- log has not been shrunk enough
WHILE (
    (@MaxMinutes*60 > DATEDIFF(ss, @StartTime, GETDATE())) AND
    (@OriginalSize = (SELECT size FROM sysfiles WHERE name = @LogicalFileName)) AND
    ((@OriginalSize * 8 / 1024) > @NewSize)
)
BEGIN --Outer loop.

    --pad out the logfile a page at a time while
    -- number of pages padded does not exceed our maximum page padding limit
    -- within time limit and 
    -- log has not been shrunk enough
    WHILE (
        (@Counter < @MaxCount) AND 
        (@MaxMinutes*60 > DATEDIFF(ss, @StartTime, GETDATE())) AND
        (@OriginalSize = (SELECT size FROM sysfiles WHERE name = @LogicalFileName)) AND
        ((@OriginalSize * 8 / 1024) > @NewSize)
    )
    BEGIN --Inner loop
        
        INSERT INTO DummyTrans VALUES ('Fill Log')  -- Because it is a char field it inserts 8000 bytes.
        DELETE FROM DummyTrans
        SELECT @Counter = @Counter + 1

        --Every 1,000 cycles tell the user what is going on
        IF ROUND( @Counter , -3 ) = @Counter
        BEGIN
            PRINT 'Padded '+LTRIM( CAST( @Counter*8 AS VARCHAR(10) ) )+'K @ '+LTRIM( CAST( DATEDIFF( ss, @StartTime, GETDATE() ) AS VARCHAR(10) ) )+' seconds';
        END
    END

    --See if a trunc of the log shrinks it.
    EXEC( @TruncLog )

END
PRINT ''

SELECT @StringData = 'Final Size of ' + db_name() + ' LOG is ' +
   CONVERT(VARCHAR(30),size) + ' 8K pages or ' + 
   CONVERT(VARCHAR(30),(size*8/1024)) + 'MB'
FROM sysfiles 
WHERE name = @LogicalFileName;

PRINT @StringData
PRINT ''

DROP TABLE DummyTrans;
PRINT '*** Perform a full database backup ***'

SET NOCOUNT OFF

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