1. It’s TEMPDB Why Should You Care?
It is more than just a little system database.
Tim Radney, Senior DBA for a top 40 US Bank
President of “Columbus GA SQL Users Group”
PASS Regional Mentor – South East USA

2. It is installed by default but what is it?
TEMPDB is the public toilet of SQL Server “quoted by many”
Temporary Objects
User Objects – triggers, queries, temporary tables, variables, etc
Internal Objects – sorts, triggers, work tables, XML variables or other LOB data type variables
Version stores – Snapshot isolation, After triggers, MARS, Online index rebuilds
Other objects that use TEMPDB
Service Broker, event notification, database mail, index creations, user-defined functions

3. Characteristics of TEMPDB
What makes this guy unique?
It is recreated each time SQL Server is started
It is modeled after the Model database
If it has grown, it is reset to its default when recreated
Can not have user defined file groups created
Auto Shrink can not be used on TEMPDB (even though it is an option)
A database snapshot can not be created on TEMPDB
THERE IS ONLY ONE TEMPDB FOR THE ENTIRE INSTANCE!

4. What are some best practices?
A good starting point for configuring TEMPDB
TEMPDB should reside on a different disk than system and user dbs
Depending on disk IO you might need to split the data and log file onto different disks as well
Size TEMPDB accordingly
Make sure instant file initialization is enabled (OS Security Policy)
Set auto grow to a fixed value, don’t use percentage
TEMPDB should be on a fast I/O subsystem
Multiple equal size data files depending on contention

5. Brand Transformation Presentation
Did I say CONTENTION?
What is contention? Wikipedia = “competition by users of a system for the facility at the same time”
Latch contention on allocation pages
Extent allocations are tracked and managed in the data files by allocation pages.
PFS – Page Free Space. One PFS page per .5 GB of data file. Tracks how much free space each page has. Page 1 in the data file. Repeats every pages.
GAM – Global Allocation Map. One GAM page per 4 GB of data file. Tracks extents. Page 2 in the data file. Repeats every 511,232 pages.
SGAM – Shared Global Allocation Map. One SGAM page per 4 GB of data file. Tracks extents being used as shared extents. Page 3 in the data file. Repeats every 511,232 pages

6. Brand Transformation Presentation
How to find contention in TEMPDB
sys.dm_os_waiting_tasks
Any tasks waiting on PageLatch or PageIOLatch
SELECT session_id AS sessionid,
wait_duration_ms AS wait_time_in_milliseconds,
resource_description AS type_of_allocation_contention
FROM sys.dm_os_waiting_tasks
WHERE wait_type LIKE ‘Pagelatch_%’
AND (resource_description LIKE ‘2:%’),
This query will give you the session, wait duration and resource description. Resource Description is <database ID>:<file ID>:<page number>.
Formula for page type is
PFS (Page ID -1) / 8088
GAM (Page ID -2) /
SGAM (Page ID – 3) /

7. Brand Transformation Presentation
You have contention, now what?
Contention causes transactions to queue causing extended wait times.
Add more data files
How many? 1 per core, 1 per 2 cores, 1 per 4 cores
Microsoft still states 1 data file per core
In real life it depends on concurrent processes
Don’t over do it - to many files can have negative impact
Create equal size files. MSSQL uses proportional fill model meaning a larger file will be used more than the others.
Multiple data files help reduce contention since each file has its own GAM, SGAM and PFS information.
database can lead to fragmentation.

8. Other tips? Troubleshoot TEMPDB I/O like you would any other database
Put TEMPDB on your fastest possible drives
Put TEMPDB on the fastest RAID you can support
Options for more IOPs
Put data files and log file on different sets of disks
Split the individual data files to different sets of disks
Need more IOPs
Visit FUSIONIO.COM. GO with SSD’s, with over 100,000 IOPs

9. QUIZ Were you paying attention? How often should you back up TEMPDB?
How many data files per core?
How often should you shrink TEMPDB?
Where should you place your TEMPDB data and log files?
What does PFS, GAM and SGAM mean?

10. Helpful Resources
#sqlhelp #sqlpass
#sqlsat97 #sqljobs

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