1. Wonder TempDB
Dubi Lebel
Dad, chef, gardener and
DBA
Dubi.lebel@gmail.com

2. Who am I?
 Dubi- Or Not To Be
 To do is to be - Descartes
 To be is to do - Voltaire
 Do be do be do - Frank Sinatra
 Yaba Daba Do - Fred Flintstone
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3. Temporary Agenda
 It all about TemDB
 For what?
 Where?
 How to?
 best practice!
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4. TempDB
 Only one TempDB per instance.
 Operations within TempDB are minimally logged.
 data in TempDB does not persist after SQL Server shuts
down.
 Only one file group in TempDB is allowed for data and
one file group for logs.
 By default auto grow is enabled.
 When the server restarts, the TempDB file size is reset
to the configured value (the default is 8 MB).
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5. What is TempDB
BOL:
The TempDB system database is a global resource that is
available to all users connected to the instance of SQL
Server and is used to hold the following:
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6. BOL: TempDB hold the following :
 Temporary user objects that are explicitly
created, such as: global or local
 temporary tables,
 temporary stored procedures,
 table variables,
 Cursors (Key-set-driven and static cursors ).
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7. BOL: TempDB hold the following :
 Internal objects that are created by the SQL Server
Database Engine, for example:
 work tables to store intermediate results for:
 spools
 sorting.
 Hash match.
 Index (create with SORT_IN_TempDB )
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8. BOL: TempDB hold the following :
 Row versions that are generated by data
modification transactions in a database that uses read-
committed
 using row versioning isolation
 snapshot isolation transactions.
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9. BOL: TempDB hold the following :
 Row versions that are generated by data
modification transactions for features, such as:
 online index operations,
 Multiple Active Result Sets (MARS),
 AFTER triggers.
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10. Is that all?
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11. TempDB also hold the following:
 DBCC CHECK
 Service Broker
 Database Mail (Service Broker)
 Event notifications (Service Broker)
 Query notifications (Service Broker)
 XML
 Common table expression queries (with cte(col,col) as select..)
 Large object (LOB) data type variables and parameters
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12. event log:
Source: MSSQLSERVER
Event ID: 17052
Description: The log file for database 'TempDB' is full.
Back up the transaction log for the database to free up
some log space
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13. error message
Server: Msg 8624, Level 16, State 1
Internal SQL Server error
or
Server: Msg 1101, Level 17, State 10, Line 1
Could not allocate new page for database 'TempDB'.
There are no more pages available in filegroup
DEFAULT. Space can be created by dropping objects,
adding additional files, or allowing file growth.
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14. How to plan TempDB Capacity ?
 Check that auto-grow is on or off for TempDB
 Execute individual queries , workload trace files , index
maintenance and monitor TempDB space.
 Sum the space-use values from the previous steps to
predict your total workload usage.
 adjust this value. And adjust again.
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15. How to Monitor TempDB Use?
 sys.dm_db_file_space_usage - disk space that is used
 sys.dm_db_session_space_usage and
sys.dm_db_task_space_usage - page allocation or
deallocation activity
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16. Monitoring TempDB Disk Space 1
SELECT
SUM(unallocated_extent_page_count) AS [free pages],
(SUM(unallocated_extent_page_count)*1.0/128) AS
[free space in MB]
FROM sys.dm_db_file_space_usage;
returns the total number of free pages and total free
space in megabytes (MB) available in all files in
TempDB
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18. Monitoring TempDB Disk Space 2
SELECT SUM(version_store_reserved_page_count)
AS [version store pages used],
(SUM(version_store_reserved_page_count)*1.0/128)
AS [version store space in MB]
FROM sys.dm_db_file_space_usage;
returns the total number of pages used by the version
store and the total space in MB used by the version store
in TempDB
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20. Monitoring TempDB Disk Space 3
SELECT transaction_id
FROM
sys.dm_tran_active_snapshot_database_transactions
ORDER BY elapsed_time_seconds DESC;
If the version store is using a lot of space in TempDB, you
must determine what is the longest running transaction.
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22. Monitoring TempDB Disk Space 4
SELECT SUM(internal_object_reserved_page_count)
AS [internal object pages used],
(SUM(internal_object_reserved_page_count)*1.0/128)
AS [internal object space in MB]
FROM sys.dm_db_file_space_usage;
returns the total number of pages used by internal objects
and the total space in MB used by internal objects in
TempDB
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24. Monitoring TempDB Disk Space 5
SELECT SUM(user_object_reserved_page_count)
AS [user object pages used],
(SUM(user_object_reserved_page_count)*1.0/128)
AS [user object space in MB]
FROM sys.dm_db_file_space_usage;
returns the total number of pages used by user objects
and the total space used by user objects in TempDB.
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26. Monitoring TempDB Disk Space 6
SELECT SUM(size)*1.0/128 AS [size in MB]
FROM TempDB.sys.database_files
returns the total amount of disk space used by all files
in TempDB.
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28. SELECT
SUM (user_object_reserved_page_count)*8 as
usr_obj_kb,
SUM (internal_object_reserved_page_count)*8 as
internal_obj_kb,
SUM (unallocated_extent_page_count)*8 as
freespace_kb,
SUM (mixed_extent_page_count)*8 as
mixedextent_kb
FROM sys.dm_db_file_space_usag
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30. which Transact-SQL statements are
the top consumers of tempdb space
 SELECT t1.session_id, t1.request_id,
t1.task_alloc, t1.task_dealloc, t2.sql_handle,
t2.statement_start_offset, t2.statement_end_offset,
t2.plan_handle FROM (Select session_id,
request_id, SUM(internal_objects_alloc_page_count)
AS task_alloc, SUM
(internal_objects_dealloc_page_count) AS
task_dealloc
FROM sys.dm_db_task_space_usage
GROUP BY session_id, request_id) AS
t1, sys.dm_exec_requests AS t2 WHERE t1.session_id
= t2.session_id AND (t1.request_id = t2.request_id)
ORDER BY t1.task_alloc DESC
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31. Perfmon counters
 Access Methods::Worktables Created/sec
 temporary objects and are used to store results for query
spool, LOB variables, and cursors.
 Typically this number is < 200
 Access Methods::Workfiles Created/sec
 temporary results for hash joins and hash aggregates
 Access Methods: Worktables From Cache Ratio
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32. Perfmon counters
 Temp Tables Creation Rate (SQL Server 2005)
 The number of temporary table or variables created/sec.
 Temp Tables For Destruction (SQL Server 2005)
 The number of temporary tables or variables waiting to be
destroyed by cleanup system thread.
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33. How to add space to TempDB?
 ALTER DATABASE, the data file will return to the new
size every time you restart the instance of SQL Server.
 Set the recovery model of TempDB to SIMPLE.
 Turn on auto-grow, but be careful, % can be dangers!
based it on the speed of the I/O subsystem
 BUT it is a good idea to turn off the auto-grow feature
for the TempDB data files
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34. Hardware
 Generally, RAID 1+0 provides better write performance
than any other RAID level providing data protection,
including RAID 5.
 Striping recommended
 Separate from user databases
 SQL Server 2008
 CHECKSUM for new installs (Earlier versions – NONE, Not
changeable)
 On upgrade NONE still default
 Recommend setting CHECKSUM after upgrade
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35. File Placement
 On a high-performance IO subsystem
 Preferably on a separate spindle(s)
 IO subsystem requirements not as strict
 Durability not required (KB917047)
 RAM Disk or IO subsystem with cache
 multiple files on the same physical spindle or multiple
devices?
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36. Number of Files
 create as many files as needed to maximize disk
bandwidth.
 One of the best practice is to create one data file for
each (virtual) CPU on the server
 KB 328551 -
 Trace flag 1118 switches allocations in TempDB from
single-page at a time for the first 8 pages
 create the files with equal sizing
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37. equal sizing
The equal sizing of data files is critical because the
proportional fill algorithm is based on the size of the
files. If data files are created with unequal sizes, the
proportional fill algorithm tries to use the largest file
more for GAM allocations instead of spreading the
allocations between all the files, thereby defeating the
purpose of creating multiple data files.
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38. Moving TempDB from system disk
Alter database TempDB modify file
(name = tempdev,
filename = „DEV:MyPathTempDB.mdf')
Alter database TempDB modify file
(name = templog,
filename = „DEV:MyPathtemplog.ldf')
Restart server
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39. What about the log file?
 Most operations in tempdb are not logged.
 Operations on user objects are logged.
 Sort operations in tempdb also require logging.
 Estimating the log space:
 similar to estimating the log file size for other databases.
 Multi log files?
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40. Moving TempDB from system disk
 Be careful when you move the TempDB database
because if the TempDB database cannot be created,
SQL Server will not start. If the TempDB database
cannot be created, start SQL Server by using the (-f)
startup parameter and move the TempDB database to a
valid location.
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41. What about Shrinking files?
 Auto shrink is not allowed for tempdb.
 How to shrink the TempDB database in SQL Server
http://support.microsoft.com/kb/307487
It is not recommended!
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42. What about auto update stats?
 disabling the auto update stats
 Usually objects created in the TempDB are fairly small
and, as such, the statistics will not reach the threshold
that causes the statistics to update automatically.
 However, you'll need to manually update statistics if you
occasionally use large temporary objects.
 What about “auto create statistics”
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43. Indexing temporary table
 Indexing temporary large temp tables greatly increases
TempDB performance
 use the normal CREATE INDEX command after the table
has been created.
 table variables cannot have indexes created on them.
But can have a primary key defined upon creation
using the DECLARE @variable TABLE command.
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44. Restrictions
 Adding filegroups.
 Backing up or restoring the database.
 Changing collation. The default collation is the server collation.
 Changing the database owner. TempDB is owned by dbo.
 Creating a database snapshot.
 Dropping the database.
 Dropping the guest user from the database.
 Enabling change data capture.
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45. Restrictions
 Participating in database mirroring.
 Removing the primary filegroup, primary data file, or log file.
 Renaming the database or primary filegroup.
 Running DBCC CHECKALLOC.
 Running DBCC CHECKCATALOG.
 Setting the database to OFFLINE.
 Setting the database or primary filegroup to READ_ONLY.
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46.  Working with tempdb in SQL Server 2005
http://technet.microsoft.com/en-us/library/cc966545.aspx
 Capacity Planning for TempDB
http://msdn.microsoft.com/en-us/library/ms345368.aspx
 TempDB Database
http://msdn.microsoft.com/en-us/library/ms190768.aspx
 Concurrency enhancements for the TempDB database
http://support.microsoft.com/kb/328551
 How to shrink the TempDB database in SQL Server
http://support.microsoft.com/kb/307487
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47. END or AND ?
D.O.N.T.B
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