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Archive for May, 2013

In SQL Serve 2012, we can get the default data file and log file locations using a simple T-SQL query as below:

SELECT SERVERPROPERTY('INSTANCEDEFAULTDATAPATH') AS [Default_Data_path]
,SERVERPROPERTY('INSTANCEDEFAULTLOGPATH') AS  [Default_log_path]
GO

Sample Output:

Default-Data-Path-Log-path

These parameters INSTANCEDEFAULTDATAPATH & INSTANCEDEFAULTLOGPATH are new in SQL Server 2012 and are not documented yet. Usually undocumented features like these aren’t tested rigorously which is why Microsoft says they are not intended to be used by customers.

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As of today (5/14/2013) this MSDN article says “SQL Server Agent service startup account must be a member of the SQL Server sysadmin fixed server role”

However, in one of our environments (SQL 2012) I have seen, just a public fixed server role is good enough to start the SQL Agent services and it works very well.

So is the statement mentioned in the MSDN article incorrect? looks like it is..moreover later I figured out the account (either a domain account or built-in system account) used for running any of the SQL Server services may not necessarily have a SQL login at all…sounds interesting?

Before going further on this topic let’s first understand What is a Per-Service SID?

SQL 2008 introduced this new option of SID (Security Identifier), a mechanism that assigns privileges to the SQL service itself, rather than to the account under which the service runs.

So starting SQL Server 2008+ on Windows Server 2008+ here is how Service Configuration and Access Control is managed:

  • SQL Server enables per-service SID for each of its services to provide service isolation and defense in depth
  • This per-service SID is derived from the service name (e.g. Database Engine/SQL Server Agent/SSIS/SSRS..etc) and is unique to that service
  • For example, a service SID name for the Database Engine service might be NT Service\MSSQL$<InstanceName>

Service SIDs managed to improve our security because:

  • Service isolation enables access to specific objects without the need to run a high-privilege account or weaken the security protection of the object
  • By using an access control entry that contains a service SID, a SQL Server service can restrict access to its resources

And here’s my understanding after some research

  • The account (either a domain account or built-in system account) used for running SQL Server services may not necessarily have a SQL login if the Per Service SID has a login instead
  • SQL Server DB Engine and SQL Server Agent runs as Windows services named NT SERVICE\MSSQLSERVER and NT SERVICE\SQLSERVERAGENT respectively within the Windows environment.
  • And the Service Account which we specify to run the services will be used when a process tries to reach outside of the current Windows environment.
  • Hence, the Service Startup Account will be used for off-box operations, unless it’s a built-in account like Network Service or a Virtual Account and if the server is Domain-joined, in which case the Machine Account will be used.
  • On SQL 2012 separate Service Startup account can be eliminated and the SQL Services can run as the “Virtual Accounts”, which have the same name as the Per Service SID, but which also have a system-managed password.

Always remember SQL Server Secuirty is all about Principle of Least Privilege. For more specific information refer MSDN BOL: Configure Windows Service Accounts and Permissions

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One of the Microsoft’s recommendation for optimizing the tempDB performance is to make each tempdb data file the same size.

Today, on one of our servers, I noticed there are 13 data files with different sizes as shown in the below screenshot:

tempdb1

My target here is to configure tempdb with 8 equi sized data files and one log file. So, in this case I have to delete those 5 extra data files and re-size the remaining 8 files equally.

To achieve this I followed the below simple three step process (The same procedure can be applied to any user databases as well)

-- Step1: First empty the data file
USE tempdb
GO
DBCC SHRINKFILE (tempdev12, EMPTYFILE); -- to empty "tempdev12" data file
GO

Data file won’t gets deleted unless it is empty. So before going to Step2 to delete the data file, we should first empty the data file which can be done from the Step1 above.

Note: If encountered this error Msg 2555, Level 16, State 1, Line 1 while performing the above operation, please refer to this post –> Msg 2555, Level 16, State 1, Line 1 – Error DBCC SHRINKFILE with EMPTYFILE option

--Step2: Remove that extra data file from the database
ALTER DATABASE tempdb
REMOVE FILE tempdev12; --to delete "tempdev12" data file
GO

I repeated the above two steps to delete the other files as well. Below is the screenshot after deleting the extra files

tempdb2

--Step3: Re-size the data files to target file size 
-- Use ALTER DATABASE if the target file size is greater than the current file size
USE [master]
GO
ALTER DATABASE [tempdb] 
MODIFY FILE ( NAME = N'tempdev', SIZE = 3072000KB ) --grow to 3000 MB
GO
--Use DBCC SHRINKFILE if the target file size is less than the current file size
USE [tempdb]
GO
DBCC SHRINKFILE (N'tempdev' , 3000) --shrink to 3000 MB
GO

In my case, the target file size is 3000 MB which is greater than the current file size, so I ran the ALTER DATABASE command for all the 8 files. And below is the screenshot after re-sizing the files

tempdb3

Note: The same procedure can be used for removing extra log files as well. Make sure the log file you are trying to empty do not have any active portion of the log. Run DBCC LOGINFO on your specified database, taking note of the FileId and the Status indicator (2 showing that it is an active VLF)

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