You can watch the replay for this Geek Sync webcast in the IDERA Resource Center: http://ow.ly/7OmW50A5qNs Every SQL Server system you work with has a tempdb database. In this Geek Sync, you’ll learn how tempdb is structured, what it’s used for and the common performance problems that are tied to this shared resource.

1. Understanding and
Monitoring Tempdb
June 3, 2015

2. About Me – Vicky Harp
• Product Manager with Idera
• Working with SQL Server
since 2001
• Working at Idera since 2004
• Twitter: @vickyharp
• Email: vicky.harp@idera.com

3. What is tempdb?
master model
msdb tempdb

4. How temporary is it?
• Recreated on server restart
– Reverts to last configured size
– Populated with contents of model database
• Does not run recovery
– Everything in tempdb is, well, temporary!

5. Why monitor tempdb?
Temp tables
Table
variables
Cursors
Worktables
DBCC
CHECKDB
Version Store
Online Index
Rebuilds
After Triggers

6. Tempdb Issues
File
Topology
Contention
Version
Store
Session
Space Usage

7. File Space and Topology
• Defaults
– One 8 MB data file on the C: drive
– One 1 MB log file on the C: drive
– 10% autogrow

8. File Space and Topology
• Best practices
– One 8 MB data file on the C: drive
– One 1 MB log file on the C: drive
– 10% autogrow

9. File Space and Topology
• Best practices
– Multiple pre-sized data files on a non-system
drive
– One pre-sized log file on a non-system drive
– Fixed size autogrow as a last resort

10. What Size Files?
• DBCC CHECKDB with ESTIMATEONLY
• Index size of largest index being rebuilt
• Monitor, monitor, monitor!

11. File Space and Topology
• What to check
– File location
– File count
– Available space
• How often
– Every 5 seconds forever

12. File Space and Topology
• What to check
– File location
– File count
– Available space
• How often
– After server restart
– Up to hourly for space available

13. Monitoring Files
• tempdb.sys.dm_db_file_space_usage
• tempdb.sys.database_files

14. DEMO

15. SQL Server Allocation 101
Database
Filegroup
File
Extent
Page
Record

16. SQL Server Allocation 101
Database
Filegroup
File
Extent
Page
Record

17. Pages and Records
Page Header
Row Data
96
bytes
8096
bytes
8192 bytes

18. Pages and Extents
Page 1
Page 2
Page 3
Page 4
Page 5
Page 6
Page 7
Page 8
Extent
8 KB
8 KB
8 KB
8 KB
8 KB
8 KB
8 KB
8 KB
64 KB

19. Mixed and Dedicated Extents
Tab A
Tab A
Tab A
Tab B
Tab B
Tab B
Tab C
Tab C
Tab A
Tab C
Tab B
8 KB
8 KB
8 KB
8 KB
8 KB
8 KB
8 KB
8 KB
64 KB 64 KB
64 KB

20. GAM Intervals
GAM Interval (4 GB)
1 2 63998 63999…
GAM
Page Allocation state of each extent (1-63999)
SGAM
Page Free pages in mixed extents (1-63999)

21. PFS Intervals
PFS Interval (64 MB)
1 2 3 8085 8086 8087…
PFS
Page Free space in heap and LOB pages

22. Allocation Process
File
GAM
Intervals
PFS
Intervals
GAM
Page
SGAM
Page
PFS
Page
(Extent 39)
Page
312
Page ID 2:1:312
File 1DB 2

23. Allocation Page Contention
File
1
GAM
Page
SGAM
Page
PFS
Page
2
3
4
4 3 2 1

24. Allocation Page Contention
File
1 GAM SGAM PFS
2
3
4 4
3
2
1
File
File
File
GAM SGAM PFS
GAM SGAM PFS
GAM SGAM PFS

25. Proportional Fill
File 4File 3File 2File 1
Allocation 1 Allocation 2 Allocation 3 Allocation 4

26. Proportional Fill
File 4File 3File 2
File 1
Allocation 1
Allocation 2
Allocation 3 Allocation 4

27. File Configuration
• Multiple tempdb data files
• All files the same size
• Presize files to prevent autogrow
• Log size 2x size of largest file
• Autogrow set to fixed size

28. Number of Files
• Create 1 file for every 2 or 4 logical
CPUs, to a maximum of 8
• Monitor for contention
• If contention exists, add 4 more files
• Repeat until a max of 1 file per
logical CPU

29. Trace Flags and SQL 2016
• TF1117
– Grow all files in a filegroup equally
• TF1118
– Do not use mixed extents
• Default behavior for SQL 2016

30. Contention
• What to check
– Waits on allocation objects in tempdb
• How often
– Continuously while configuring tempdb
– Weekly spot checks thereafter

31. Monitoring Contention
• sys.dm_os_waiting_tasks
• wait_type like 'PAGE%LATCH_%'
• PageID
– PFS – 1 or multiple of 8088
– GAM – 2 or multiple of 511232
– SGAM – 3 or (PageID – 1) is multiple of 511232

32. DEMO

33. Blocking
CAT
DOG
Write Read
Read

34. Snapshot Isolation
CAT
FISH
(Ver 1)
Write Read
Read
CAT
DOG
(Ver 2)
CAT
FISH
(Ver 1)
Tempdb
Version
Store

35. Snapshot Isolation
Read
Read
CAT
FISH
(Ver 1)
Tempdb
Version
Store
CAT
DOG
(Ver 2)
CAT
FISH
(Ver 3)

36. Version Store
• What to check
– Version store size
– Long running version store transactions
– Version generation and cleanup rate
• How often
– Continuously with snapshot isolation workload
– Otherwise, check with space available check

37. Monitoring Version Store
• sys.dm_db_file_space_usage
– version_store_reserved_page_count
• sys.dm_tran_active_snapshot_database_transactions
• sys.dm_os_performance_counters
– Version Generation rate (KB/s)
– Version Cleanup rate (KB/s)

38. DEMO

39. Session Space Usage
Temp tables
Table
variables
Cursors
Worktables
DBCC
CHECKDB
Version Store
Online Index
Rebuilds
After Triggers

40. Tempdb Spills
Operation RAM
Tempdb
Disk

41. Session Space Usage
• What to check
– Heavy use of tempdb by user sessions
• How often
– Continuously if tuning workload
– Otherwise, daily spot checks

42. Monitor Session Space Used
• tempdb.sys.dm_db_session_space_usage
• tempdb.sys.dm_db_task_space_usage

43. DEMO

44. Tempdb Issues
File
Topology
Contention
Version
Store
Session
Space Usage

45. THANK YOU!
vicky.harp@idera.com
http://community.idera.com
Q&A Coming Up!