Two things I'd like to know:
- how do you safely move tempdb with minimal downtime?
- how many tempdb files do you need?
Is it 1 file per core? So quad-core = 4 tempdb files, creating three new ones?
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tempdb files, you simply need to do the following:
alter database tempdb modify file ( name = tempdev, filename = 'C:\YourNewTempdbDir\tempdb.mdf' ) go alter database tempdb modify file ( name = templog, filename = 'C:\YourNewTempdbDir\templog.ldf' ) go
If you want to add a new file to
tempdb, you simply need to do the following (provided you want to add it to the
PRIMARY filegroup, or create your own):
alter database tempdb add file ( name = tempdb2, filename = 'C:\YourNewTempdbDir\Tempdb2.ndf' ) go
For these changes to take effect, you will need to restart the SQL Server service. So as far as minimizing downtime goes, you are constrained to the amount of time it will take for the service restart. You don't have to worry about moving the pre-existing
tempdb database files, as SQL Server always recreates the files and the new locations/files will be created upon service startup.
As for the "1 tempdb data file per core", that is largely a myth. The correct approach is to monitor
tempdb file contention for the Page Free Space (PFS), Global Allocation Map (GAM), and the Shared Global Allocation Map (SGAM) pages. Please reference this article to get a query (alternative link) that looks through the
sys.dm_os_waiting_tasks DMV to see how much
tempdb file contention there is. Then you need to go off of this, instead of just blanketing
tempdb with the same amount of files as there are cores. It's the more advisable approach.
To move tempdb, execute:
ALTER DATABASE tempdb MODIFY FILE ( name=tempdev, filename='D:\Newpath\tempdb.mdf') GO ALTER DATABASE tempdb MODIFY FILE ( name=templog, filename='D:\Newpath\templog.ldf') GO
Then restart your SQL Server Service (MSSQLServer).
Number of files in tempdb - see Paul Randall's article: A SQL Server DBA myth a day: (12/30) tempdb should always have one data file per processor core
From Microsoft's advice:
As a general rule, if the number of logical processors is less than or equal to 8, use the same number of data files as logical processors.
If the number of logical processors is greater than 8, use 8 data files and then if contention continues, increase the number of data files by multiples of 4 (up to the number of logical processors) until the contention is reduced to acceptable levels or make changes to the workload/code.
Moving the TempDB files is a 2-step process:
SQL Serverservice for the change to take effect (this is the minimum downtime you need)
To tell SQL where to create the new TempDB files, you can use:
DECLARE @newDriveAndFolder VARCHAR(8000); SET @newDriveAndFolder = 'Z:\YourTempDBfolder'; SELECT [name] AS [Logical Name] ,physical_name AS [Current Location] ,state_desc AS [Status] ,size / 128 AS [Size(MB)] --Number of 8KB pages / 128 = MB ,'ALTER DATABASE tempdb MODIFY FILE (NAME = ' + QUOTENAME(f.[name]) + CHAR(9) /* Tab */ + ',FILENAME = ''' + @newDriveAndFolder + CHAR(92) /* Backslash */ + f.[name] + CASE WHEN f.[type] = 1 /* Log */ THEN '.ldf' ELSE '.mdf' END + '''' + ');' AS [Create new TempDB files] FROM sys.master_files f WHERE f.database_id = DB_ID(N'tempdb') ORDER BY f.[type];
This will generate the T-SQL statements you need to run to move the files to the new
drive:\folder you want. (click image to make larger)
When you have ran your moving statements, you can run the above query again, to check that the
Current Location column is now showing your new
Once you're happy with your changes, restart the SQL Server service.