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Be Careful Using LiteSpeed Extended Stored Procedures With SQL Agent

By Dewey Wu,

Quest LiteSpeed is one of the options to create compressed backups with SQL Server 2005. It’s uncommon that a SQL Server DBA needs to create a customized backup and restore routine for an application using combination of LiteSpeed extended stored procedures. For example, in a quarterly basis, you may want to take file group backup of the primary file group and some secondary file groups which contain more recent data. After taking the backup, you may want to perform a restore test against the resulting backup file. In this case, a SQL Agent job scheduled quarterly with two steps – one to call xp_backup_database to create the backup, another to invoke xp_restore_database to perform a restore and then a simple data query - would be an obvious option. However, you should be really careful when you are implementing such a solution.

Issue


To better describe the issue, let’s first reproduce it on a machine with SQL Server 2008 R2 and LiteSpeed 6.0 installed, with the following steps.

  1. Create a SQL Agent job on the server named “Test LiteSpeed Extended Stored Procedure”.
  2. Create a new job step named “T-SQL Approach”. Set the type to “Transact-SQL script (T-SQL)”.
  3. Put the SQL statements below in command textbox.
  4. Save the job and run it.
begin try
  exec master.dbo.xp_restore_verifyonly @filename = 'any invalid filename'
end try
begin catch
  print 'I am in trouble.'
end catch
print 'I am good.'

The outcome of the job will be an error message like this, with neither the words “I am good” nor “I am in trouble”.

Message
Executed as user: NT AUTHORITY\NETWORK SERVICE. LiteSpeed(R) for SQL Server Version 6.0.1.1007 Copyright 2010 Quest Software, Inc. [SQLSTATE 01000] (Message 1)  The system cannot find the file specified.   LiteSpeed for SQL Server could not open backup file: (C:\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\Backup\any invalid filename). The previous system message is the reason for the failure. [SQLSTATE 42000] (Error 50002).  The step failed.

The same SQL statements give the following error if they are executed in SQL Management Studio (SSMS) or in sqlcmd utility.

LiteSpeed(R) for SQL Server Version 6.0.1.1007
Copyright 2010 Quest Software, Inc.

Msg 50002, Level 16, State 1, Line 0
The system cannot find the file specified.

LiteSpeed for SQL Server could not open backup file: (D:\MSSQL.1\MSSQL\Backup\any invalid filename).
The previous system message is the reason for the failure.

I am good.

The comparison of the different outcomes tells us two things regarding to SQL Agent job:

  • The try catch block has failed to catch the exception thrown by the LiteSpeed extended stored procedure.
  • The exception actually stops SQL Agent job from executing further, while in SSMS or sqlcmd it’s not the case.

Whilst you may evaluate whether the operation is successfully by checking the returning value of the stored procedure (zero stands for success and non-zero stands for failure), you can do nothing to recover the failure or even to record it because the job terminates immediately upon the exception. This is terrible when you need to program some conditional logic or some logging in the backup and restore routine.

Workaround

As you may have guessed, the workaround to the issue is as simple as using sqlcmd instead of T-SQL in the SQL Agent job step. Since sqlcmd would not throw any exception to SQL Agent job, the job will be running successful anyway unless there is a connection issue or other system level issues. In this way you will have full control of the code no matter the LiteSpeed extended stored procedures throws exception or not. You will also be very flexible to either put in exception handling code according to the error code returned by the stored procedures, or just log it somewhere.

Further Discussion

It’s still unclear that why SQL Agent job behaves in such way. I have also examined if there is any T-SQL SET statement could suppress the LiteSpeed exception but in vain. Any comments are welcome.

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