SQL Server – Convert Timestamp in dm_os_ring_buffers

I am struggling to find the reason of the arithmetic overflow. why is it happening?

Most likely the metadata is returning some unexpected values that your code cannot handle. For example:

-- Example values returned from sysfiles and FILEPROPERTY
DECLARE 
    @size integer = 1,
    @spaceused integer = 10000;

-- The essence of the code in the question
SELECT
    CAST
    (
        100 * 
        (
            CAST 
            (
                (
                    (@size/128.0 - @spaceused/128.0)/(@size/128.0)
                )  
                AS decimal(5,2)
            )
        ) 
        AS varchar(8)
    ) + '' AS FreeSpacePct;

...returns the error mentioned in the question, because the computed (negative!) value will not fit in decimal(5,2).

There are reasons why size might be reported as much lower than space used, including tempdb file growths, filestream files, bugs in older versions of SQL Server...too many to list. You could/should code defensively against this possibility (and also for offline/defunct files...and so on).

The question is tagged SQL Server 2014, so there's no need to use the deprecated sys.sysfiles view (for backward compatibility with SQL Server 2000):

I might write this query as:

SELECT
    DatabaseName = DB_NAME(),
    [FileName] = DF.name,
    FileType = DF.type_desc,
    SizeMB = STR(DF.size * Factor.PagesToMB, 10, 2),
    SpaceUsedMB = STR(FP.SpaceUsed * Factor.PagesToMB, 10, 2),
    FreeSpaceMB = STR(FS.FreeSpace * Factor.PagesToMB, 10, 2),
    FreeSpacePct =  STR(Factor.ToPct * FS.FreeSpace / DF.size, 7, 4)
FROM sys.database_files AS DF
CROSS APPLY (SELECT FILEPROPERTY(DF.name, 'SpaceUsed')) AS FP (SpaceUsed)
CROSS APPLY (SELECT DF.size - FP.SpaceUsed) AS FS (FreeSpace)
CROSS JOIN  (SELECT 8e0 / 1024e0, 1e2) AS Factor (PagesToMB, ToPct);

Main advantages:

• It separates out the calculation steps
• Uses float arithmetic to avoid overflows
• STR formats the result and does not raise an error on overflow
• It does not cause the error in the question to be thrown

A dynamic SQL version (to collect information for all databases):

DECLARE @SQL nvarchar(2000);

SET @SQL = N'
USE ?;

SELECT
    DatabaseName = DB_NAME(),
    [FileName] = DF.name,
    FileType = DF.type_desc,
    SizeMB = STR(DF.size * Factor.PagesToMB, 10, 2),
    SpaceUsedMB = STR(FP.SpaceUsed * Factor.PagesToMB, 10, 2),
    FreeSpaceMB = STR(FS.FreeSpace * Factor.PagesToMB, 10, 2),
    FreeSpacePct =  STR(Factor.ToPct * FS.FreeSpace / DF.size, 7, 4)
FROM sys.database_files AS DF
CROSS APPLY (SELECT FILEPROPERTY(DF.name, ''SpaceUsed'')) AS FP (SpaceUsed)
CROSS APPLY (SELECT DF.size - FP.SpaceUsed) AS FS (FreeSpace)
CROSS JOIN  (SELECT 8e0 / 1024e0, 1e2) AS Factor (PagesToMB, ToPct);
';

DECLARE @Results AS table
(
    DatabaseName sysname NOT NULL,
    [FileName] sysname NOT NULL,
    FileType nvarchar(60) NOT NULL,
    SizeMB char(10) NULL,
    SpaceUsedMB char(10) NULL,
    FreeSpaceMB char(10) NULL,
    FreeSpacePct char(7) NULL
);

INSERT @Results
EXECUTE sys.sp_MSforeachdb
    @command1 = @SQL;

SELECT R.*
FROM @Results AS R
ORDER BY R.DatabaseName; -- Or whatever

Usual caveats about using sp_MSforeachdb.

The TRY...CATCH block is causing the execution of the stored procedure to terminate before it has a chance to return the values in #TEMP.

Try this stored proc:

IF OBJECT_ID('dbo.SomeProc') IS NOT NULL
DROP PROCEDURE dbo.SomeProc;
GO
CREATE PROCEDURE [dbo].[SomeProc]
AS 
BEGIN
    CREATE TABLE #TEMP
    (
        ID INT NOT NULL
    );

    INSERT INTO #TEMP 
    VALUES (1);

    INSERT INTO #TEMP 
    VALUES (1/0);

    PRINT (N'Run the SELECT');

    SELECT ID 
    FROM #TEMP;
END
GO

Running it, like this, without a TRY...CATCH, allows all the statements in the proc to run:

EXEC dbo.SomeProc;

The output:

Msg 8134, Level 16, State 1, Procedure SomeProc, Line 12
Divide by zero error encountered.
The statement has been terminated.
Run the SELECT

However, if you run it inside a TRY...CATCH:

BEGIN TRY
    EXEC dbo.SomeProc;
END TRY
BEGIN CATCH
    PRINT (ERROR_MESSAGE());
END CATCH

You see only the error message:

Divide by zero error encountered.

The PRINT (N'Run the SELECT'); never runs, and indeed the SELECT ID FROM #TEMP; never runs either. Hence no rows are returned, and nothing can be inserted into your #TEMPTABLE

From the MSDN documentation on TRY...CATCH:

If there is an error in the code that is enclosed in a TRY block, control passes to the first statement in the associated CATCH block.

As always, the devil is in the details. TRY...CATCH always aborts the code inside the BEGIN TRY...END TRY code block if any error over severity 10 occurs that does not close the database connection. Execution is immediately passed into the BEGIN CATCH...END CATCH block, even if this means aborting code in a stored proc.

Be aware that if an error occurs on any row the entire insert will not happen. The only reason you're seeing this error, and a row being inserted, is because you have two insert statements, one that runs to completion, and one that throws an error. Take for instance:

IF OBJECT_ID('dbo.SomeProc') IS NOT NULL
DROP PROCEDURE dbo.SomeProc;
GO
CREATE PROCEDURE [dbo].[SomeProc]
AS 
BEGIN
    CREATE TABLE #TEMP
    (
        ID INT NOT NULL
    );

    INSERT INTO #TEMP 
    VALUES (1);

    INSERT INTO #TEMP 
    VALUES (1)
        , (2)
        , (3)
        , (4)
        , (1/0);

    PRINT (N'Run the SELECT');

    SELECT ID 
    FROM #TEMP;
END
GO

Using this stored proc, either inside a TRY...CATCH or with no TRY...CATCH block, will only result in a single row being inserted into the #TEMPTABLE - none of the rows in the 2nd insert will be present in the output.