How to Back Up the Transaction Log When the Database Is Damaged

This is one of the best and most frequently asked question in the SQL DBA interview especially if you are being interview for "Production Support DBA" role. "How to Back Up the Transaction Log When the Database Is Damaged" aka "how to perform tail log backup" - you will face this kind of issues when your database which get corrupted and goes in suspect most while in use or when you recover from a server crash mostly in cases like disk failures. When such failures occur your best method to recover the data is to restore your backup (full/diff/t.logs), so when do we need the tail log backups ? Assume a case like this one - you take a full backup every night and differentials every 4 hrs. and t.log backups every 15 minutes, which most of us do. Suppose your t.log backup was about to start at 11:15 AM and crash happens at 11:13 AM. So, we are left with a gap of 11:00 AM to 11:13 AM transaction - how do we recover from this gap, yes we depend on tail log. There is no gurantee that you will recover best all of the data, but is a "best effort" strategy as a responsible DBA. Here is the T-SQL command, BACKUP LOG TestDB TO TestDB_FullRM_log1 WITH NO_TRUNCATE GO Notice the keyword "NO_TRUNCATE", why we need it ? - NO_TRUNCATE clause allows the active part of the t.log to be backed up even if the database is inaccessible/offline, provided the transaction log file is accessible and undamaged, this is very important so keep it in mind :) - for interview as well as for real case where you are required to recover the database from a failure.Why it's called tail log ? - because this is the last backup taken from the failed database in order to recover from failures.

SQL Job Status Reporting

One day I suddenly see that my LiteSpeed DB backup job is running and running forever ! - though it did not fail but it did not complete so its still a failure in my opinion. This can happen due to third part component failure, or due to bug in the Windows OS or in the SQL Server agent. So, for what so ever reason if job/step is hung, its an issue. To overcome this issue I decided to email out the SQL Job status as a summarised report to myself (and other as required).

Here is the script to achieve the same. It will send out an email (assuming you have configure email feature on your SQL Server) with SQL Job status like LastRun time LastRunStatus and TimeTaken for latest execution.

--===================================================

DECLARE @tableHTML NVARCHAR(MAX)

,@SubjLine varchar(500)

SET @tableHTML =

N'<H4>SQL Server Job Status Report:</H4>' +

N'<table border="1">' +

N'<tr><th>Job Name</th><th>is enable ?</th>' +

N'<th>LastRunDateTime</th><th>LastRunDuration</th><th>LastRunOutCome</th>' +

CAST ( (

SELECT

td = J.Name, '',

td = J.Enabled, '',

td = left(Jh.run_date,4) + '-' + SUBSTRING(CAST(Jh.run_date AS CHAR),5,2) + '-' + right(Jh.run_date,2) +' '+

LEFT(REPLICATE('0', 6-LEN(Jh.run_time)) + CAST(Jh.run_time AS CHAR(6)),2) + ':' +

SUBSTRING(REPLICATE('0', 6-LEN(Jh.run_time)) + CAST(Jh.run_time AS CHAR(6)),3,2) + ':' +

SUBSTRING(REPLICATE('0', 6-LEN(Jh.run_time)) + CAST(Jh.run_time AS CHAR(6)),5,2), '',

td = LEFT(REPLICATE('0', 6-LEN(Jh.run_duration)) + CAST(Jh.run_duration AS CHAR(6)),2) + ':' +

SUBSTRING(REPLICATE('0', 6-LEN(Jh.run_duration)) + CAST(Jh.run_duration AS CHAR(6)),3,2) + ':' +

SUBSTRING(REPLICATE('0', 6-LEN(Jh.run_duration)) + CAST(Jh.run_duration AS CHAR(6)),5,2), '',

td = CASE run_status

when 0 then 'Failed'

when 1 then 'Succeeded'

when 2 then 'Retry'

when 3 then 'Canceled'

when 4 then 'Progress'

end, ''

FROM msdb.dbo.sysjobhistory Jh

JOIN msdb.dbo.sysjobs J ON Jh.job_id = J.job_id

WHERE

Jh.Instance_id IN (

SELECT MAX(Jh.instance_id) [Instance_Id]--, J.Job_Id INTO #JobHist

FROM msdb.dbo.sysjobhistory Jh

JOIN msdb.dbo.sysjobs J ON Jh.job_id = J.job_id

WHERE

--Jh.step_id = 0 -- I don't step details, just job outcome

--AND J.enabled = 1 -- enable this condition to filter out DISABLED jobs

J.Name IN (SELECT JobName FROM Monitoring.dbo.SQLJobsToMonitor WHERE ReportedYesNo = 1)

GROUP BY J.Job_Id

)

ORDER BY

CONVERT(DATETIME,

left(Jh.run_date,4) + '-' + SUBSTRING(CAST(Jh.run_date AS CHAR),5,2)

+ '-' + right(Jh.run_date,2) +' '+

LEFT(REPLICATE('0', 6-LEN(Jh.run_time)) + CAST(Jh.run_time AS CHAR(6)),2) + ':' +

SUBSTRING(REPLICATE('0', 6-LEN(Jh.run_time)) + CAST(Jh.run_time AS CHAR(6)),3,2) + ':' +

SUBSTRING(REPLICATE('0', 6-LEN(Jh.run_time)) + CAST(Jh.run_time AS CHAR(6)),5,2)

)

FOR XML PATH('tr'), TYPE

) AS NVARCHAR(MAX) ) +

N'</table><br><h5>Job name: Monitoring - SQL Job Status Report<h5>' ;

SET @SubjLine = 'SQLMail Monitor: '+@@ServerName+': Job Status Report'

EXEC msdb.dbo.sp_send_dbmail

@profile_name = 'SQLMail_Mail',

@recipients = 'emailid_001;Emailid02',

@subject = @SubjLine,

@body = @tableHTML,

@body_format = 'HTML';

--===================================================

"Monitoring.dbo.SQLJobsToMonitor" is a table which will be holding the list of jobs to be reported, you can add or delete or set the flag "ReportedYesNo" column to 0/1 to filter out the less important jobs from being reported.

Here is the table structure for the same.

--===================================================

CREATE TABLE SQLJobsToMonitor (

PkId INTEGER IDENTITY PRIMARY KEY NOT NULL,

JobName varchar(500),

ReportedYesNo bit default 1

)

--===================================================

Report Sample:

SQL Server Job Status Report:

Job Name	is enable ?	LastRunDateTime	LastRunDuration	LastRunOutCome
SS Maint Job - exec Prc_FutureRevenue @Thread = 1	0	2009-03-14 01:15:17	01:56:31	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 0	0	2009-03-14 01:15:17	01:56:53	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 4	0	2009-03-14 01:15:17	01:57:10	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 9	0	2009-03-14 01:15:17	01:58:15	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 6	0	2009-03-14 01:15:17	01:58:25	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 3	0	2009-03-14 01:15:17	01:58:38	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 2	0	2009-03-14 01:15:17	01:59:18	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 5	0	2009-03-14 01:15:17	01:59:36	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 7	0	2009-03-14 01:15:17	03:22:27	Succeeded
SS Maint Job - exec Prc_FutureRevenue @Thread = 8	0	2009-03-14 01:15:17	03:23:24	Succeeded