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

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

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= 65536." Results:

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

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

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=256+576*2=1,408MB

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!

-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:

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

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

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)

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): 901904, committed (KB): 2215752, memory utilization: 40%.”

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: http://msdn2.microsoft.com/en-us/library/aa198229(SQL.80).aspx Note: Other parts of SQL may still be paged, along with other applications

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 2008 [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

DEMO: Get the Memory Statistics Observer Memory Usage DBCC MEMORYSTATUS Query Memory Objects Small Query Memory Objects sys.dm_os_wait_stats RESOURCE_SEMAPHORE http://support.microsoft.com/kb/907877 http://blogs.msdn.com/slavao/archive/2005/02/14/372309.aspx --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

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

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

DEMO: TempDB Contention

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

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

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

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

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

DEMO: TempTables/TempVariables

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

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)

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

Please Complete The Evaluations! Your Feedback and comments COUNT! Thank you! Contact me further: 31 March 2010, 16:15 – 17:15, SQL Server Unplugged Or any time at: e-mail: Margarita.Naumova@microsoft.com Magi_Naumova@hotmail.com Please Complete The Evaluations! Your Feedback and comments COUNT!

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