1. TOP 10 Thinks you shouldn’t do with/in your database
30 March 2010
TOP 10 Thinks you shouldn’t do with/in your database
Margarita Naumova
Microsoft
Thank you for this session, you were the initiators, your feedback

2. Top 10 … on focus today Memory Configuration Worst Practices
TempDB configuration worst practices
TempDB Usage worst practices

3. MaxServerMemory Configuration Mistakes
Set MaxServerMemory to physical Maximum
Do not set MaxServerMemory At All
All threads/processes outside SQL Server BufferPool are slow or cannot start at all:
Not enough buffers for SSIS Packages, releasing buffer waits
Linked Server and distributed query issues performance or execution errors
Connection/SQL Server Login Time-Outs (Errors 70x)
Error "WARNING: Failed to reserve contiguous memory of Size= "
Results:

4. The way it works 0xFFFFFFFF Operating System 0xC0000000
SQL Server
Buffer Pool
(8KB buffers)
SQL Server or OS
(/3GB switch)
MemToLeave area
Thread stacks

5. The way it works 0xFFFFFFFF Operating System 0xC0000000
SQL Server or OS
(/3GB switch)
SQL Server
MemToLeave area
Thread stacks
Other
Locks
Query Workspace.
Plan Cache
DB Page Cache
MaxServerMemory

6. Recommendations Always define MaxServerMemory!
Take into account MemToLeave area
MemToLeave = MemReserved + (NumThreads* StackSize)
MemReserved = 256 MB
NumThreads = the total number of worker threads configured (table below)
StackSize = (0.5MB x86, 2MB x64, 4MB IA64)
Example 8Cores, 64Bit: MemToLeave= *2=1,408MB

7. Recommendations Calculate worst case scenario
Scenario Examle: 64bit, 8 cores, 32GB RAM
2GB for the OS
2 GB for MemToLeave (Linked Srvs, MultiPage Allocators AND worker threads)
1GB for backup program
= 5GB
Set Max Server Memory to 27GB
Special Attention to MultiInstance Cluster Configuration!

8. -3GB/AWE configuration mistakes
Set /3G when there are other Applications on the server
/AWE and large buffer flushes
The SQL Server needs more memory because it takes all and still works slowly. I set /3G and I set AWE switch but:
The OS is hanging, the overall Server is hanging
I still do not get performance benefit
Results:

9. The way it works - /3GB 0xFFFFFFFF Operating System 0xC0000000
SQL Server or OS
(/3GB switch)
SQL Server
MemToLeave area
Thread stacks
Other
Locks
Query Workspace.
Plan Cache
DB Page Cache

10. The way it works - AWE 0xFFFFFFFF Operating System 0xC0000000
SQL Server or OS
(/3GB switch)
SQL Server
MemToLeave area
Thread stacks
Other
Locks
Query Workspace.
Plan Cache
DB Page Cache
AWE
Memory

11. Recommendations
Use /3GB only in 32bit platforms and only when you have not database page buffer related memory issues
Use AWE on 32-bit to increase DB Pages BufferPool Size if you have intensive BPool Page Usage
Watch out Memory\Free System Page Table Entries counter (should be >10 000)
/USERVA switch in Windows Server 2003
Gives less than 3GB to user mode
Extra space kept in reserve for System PTEs
Recommended values between 2900 and 3030
Do not use /PAE with /3GB (it increases PTE from 4K to 8K)

12. The LockPagesInMemory Mistakes
LockPagesInMemory Not set
The performance of SQL Server decreases suddenly.
A computer that is running SQL Server stops responding for a short time.
A time-out occurs for applications that connect to SQL Server.
Problems occur when you run even simple commands or use applications on the system
New message from 2005 SP2:
“A significant part of sql server process memory has been paged out. This may result in a performance degradation. Duration: 646 seconds. Working set (KB): , committed (KB): , memory utilization: 40%.”

13. The way it works - LockPagesInMemory
Prevent OS paging of Buffer Pool by Locking Pages in Memory
Automatic if SQL Server Service Account has Lock Pages in Memory privilege
Enterprise and Standard Edition Feature
Set using gpedit.msc:
Note: Other parts of SQL may still be paged, along with other applications

14. Recommendations On 64bit configuration always set LockPagesInMemory
Use with MaxServerMemory
SQL Server 2008 SP1 CU2 and SQL Server 2005 SP3 CU 4 for Standard Editions
For the LocalSystem account it is set automatically
Note For 64-bit editions of SQL Server, only SQL Server Enterprise Edition can use the Lock pages in memory user right. This is applicable for SQL Server 2005 [RTM, SP1, SP2, SP3] and for SQL Server [RTM and SP1]. SQL Server 2008 SP1 Cumulative Update 2 and SQL Server 2005 SP3 Cumulative Update 4 introduce support for SQL Server Standard editions to use the Lock pages in memory user right

15. DEMO: Get the Memory Statistics
Observer Memory Usage
DBCC MEMORYSTATUS
Query Memory Objects
Small Query Memory Objects
sys.dm_os_wait_stats
RESOURCE_SEMAPHORE
--Obtain memory Info
select * from sys.dm_os_sys_info
DBCC MemoryStatus
select * from sys.dm_os_memory_clerks
select * from sys.dm_os_performance_counters
--Target v/s Total
--Woru memory

16. The TempDB configuration mistakes
Usage  Wrong DB File Sizing
Contention  Wrong Number of DB Files
Placement  Wrong Drive
Issues:
Slow Execution of procedures
Slow execution on large queries
Disruption/Prevent procedure from completion
1101- insufficient space for session
1105 – insufficient space for session
3959 – version store is full
3967 – version store forced to shrink
3958 – transaction cannot find required version record …
Too much or too less (1) TempDB Database File
Confuse TempDB Performance and contention
Extreme TempDB usage for large temp objects, and object generating volumes
TempDB Size left default
Temp Tables v/s temp variables v/s … huge user temp objects

17. Contention defined On TempTables Creation latching tempdb PFS SGAM
4 GB
latching

18. DEMO: TempDB Contention

19. User Objects User-defined tables and indexes System tables and indexes
Global temporary tables and indexes
Local temporary tables and indexes
Table variables
Tables returned in table-valued functions
Scoped to session or stored procedure

20. Temp Tables v/s temp Variables
Common myth that table variables are memory-based only
Both end up hitting tempdb
Temp Tables
Can be indexed
Can have statistics
Colmodctr can cause recompiles
Table Variables
No indexes or statistics
No recompile threshold

21. Internal Objects Not logged Work tables for cursor operations
Work tables for spool operations
Temporary large object storage
Work files for hash join or hash aggregate operations
Intermediate sort results for creating/rebuilding indexes (if SORT_IN_TEMPDB) or some GROUP BY, ORDER BY or UNION queries

22. Sort Warnings Reason: large sort operation within a query (ORDER BY)
Sort Operation cannot be done into memory and has to be divided into more steps
Sort takes multiple passes to TempDB to get the sorted output

23. Hash Warnings
Hash Occursion/hash bailout has occurred during hash operation
Hash Join or Hash aggregate has run out of memory and been force to split to disk during execution
Slower query perf and space consumtion increase in TempDB

24. DEMO: TempTables/TempVariables

25. Recommendations Minimize use of temporary tables
Avoid Static Cursors usage
Watch out usage of LOB,
Index to avoid worktables/workfiles
Set the size appropriately for production
Enable autogrow
Use Instant File Initialization
Set Number of files to ½ to ¼ CPUs but <=8
Set equal file sizes
Place separately
Separate drive for Files and Log
Fast IOPS drive

26. Recommendations (cont)
Minimize large sort operations trough:
Reducing the sort inputs
Reducing the fields in ORDER BY clause
Creating appropriate index
Minimize Hash Joins
Make sure that statistics exist on the columns that are involved in the hashing operation
Try updating them
Try using different type of JOIN (nested loop, merge)

27. Top 10 thinks you should do with/in your database (server) Session Summary
Don’t miss MaxServerMemory
Don’t use /3GB and /AWE for 32bit platforms just because you guess that SQL server needs more Memory
Don’t miss the LockPagesInMemory on 64bit platform
Don’t confuse TempDB performance with contention
Don’t use too much/few TempDB Data Files
Don’t leave TempDB File Size default. Size properly
Don’t just use TempTables or TempVariables. Choose properly
Don’t use Static Cursors
Don’t do large ORDER BY
Avoid Large Inputs, groupings causing hash operations

28. Please Complete The Evaluations! Your Feedback and comments COUNT!
Thank you!
Contact me further:
31 March 2010, 16:15 – 17:15, SQL Server Unplugged
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Please Complete The Evaluations! Your Feedback and comments COUNT!

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