Recommend MaxDop settings for SQL Server

The Microsoft SQL Server max degree of parallelism (MAXDOP) configuration option controls the number of processors that are used for the execution of a query in a parallel plan. This option determines the computing and thread resources that are used for the query plan operators that perform the work in parallel. Depending on whether SQL Server is set up on a symmetric multiprocessing (SMP) computer, a non-uniform memory access (NUMA) computer, or hyperthreading-enabled processors, you have to configure the max degree of parallelism option appropriately.

When setting up a new SQL Server, I usually use the following code to determine a good starting point for the MAXDOP setting:

I recommend setting MAXDOP to a setting that makes sense for your server load. Only you can determine the best setting for your environment. This script is just a good way to start.

Determining a setting for Cost threshold for parallelism

The cost threshold for parallelism option specifies the threshold at which SQL Server creates and runs parallel plans for queries. SQL Server creates and runs a parallel plan for a query only when the estimated cost to run a serial plan for the same query is higher than the value set in cost threshold for parallelism.

The default is set to 5, which is a really low setting. Although there is no right and wrong number, I’d recommend starting with this setting at 50 or so and tuning up or down as appropriate.

The following script returns a list of parallel query plans and their subtree costs which will help you decide an appropriate number.

SQL Server ignores the cost threshold for parallelism value under the following conditions:

  • Your computer has only one processor.
  • Only a single CPU is available to SQL Server because of the affinity mask configuration option.
  • The max degree of parallelism option is set to 1.

core AS (
eqp.query_plan AS [QueryPlan],
ecp.plan_handle [PlanHandle],
q.[Text] AS [Statement],
n.value('(@StatementOptmLevel)[1]', 'VARCHAR(25)') AS OptimizationLevel ,
ISNULL(CAST(n.value('(@StatementSubTreeCost)[1]', 'VARCHAR(128)') as float),0) AS SubTreeCost ,
ecp.usecounts [UseCounts],
ecp.size_in_bytes [SizeInBytes]
sys.dm_exec_cached_plans AS ecp
CROSS APPLY sys.dm_exec_query_plan(ecp.plan_handle) AS eqp
CROSS APPLY sys.dm_exec_sql_text(ecp.plan_handle) AS q
CROSS APPLY query_plan.nodes ('/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple') AS qn ( n )

SubTreeCost * UseCounts [GrossCost],
--GrossCost DESC
SubTreeCost DESC

Fore more details: Cost Threshold for Parallelism Option

Finding Implicit Column Conversions in the Plan Cache

I’m just sharing with you guys a script to find all implicit data type conversions associated with mismatched data types in a specific database.
It’s pretty handy when you are either developing or coding reviewing.


SET @dbname = QUOTENAME(DB_NAME()); 

   (DEFAULT '')
   stmt.value('(@StatementText)[1]', 'varchar(max)'),
   t.value('(ScalarOperator/Identifier/ColumnReference/@Schema)[1]', 'varchar(128)'),
   t.value('(ScalarOperator/Identifier/ColumnReference/@Table)[1]', 'varchar(128)'),
   t.value('(ScalarOperator/Identifier/ColumnReference/@Column)[1]', 'varchar(128)'),
   ic.DATA_TYPE AS ConvertFrom,
   t.value('(@DataType)[1]', 'varchar(128)') AS ConvertTo,
   t.value('(@Length)[1]', 'int') AS ConvertToLength,
FROM sys.dm_exec_cached_plans AS cp
CROSS APPLY sys.dm_exec_query_plan(plan_handle) AS qp
CROSS APPLY query_plan.nodes('/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple') AS batch(stmt)
CROSS APPLY stmt.nodes('.//Convert[@Implicit="1"]') AS n(t)
   ON QUOTENAME(ic.TABLE_SCHEMA) = t.value('(ScalarOperator/Identifier/ColumnReference/@Schema)[1]', 'varchar(128)')
   AND QUOTENAME(ic.TABLE_NAME) = t.value('(ScalarOperator/Identifier/ColumnReference/@Table)[1]', 'varchar(128)')
   AND ic.COLUMN_NAME = t.value('(ScalarOperator/Identifier/ColumnReference/@Column)[1]', 'varchar(128)')
WHERE t.exist('ScalarOperator/Identifier/ColumnReference[@Database=sql:variable("@dbname")][@Schema!="[sys]"]') = 1

More details here:

Clearing a Single Plan from Cache

Most of you guys know that you can clear all cached plans using DBCC FREEPROCCACHE.
In SQL Server 2008 you are able to clean a single pan from cache. The query below helps you to find the plan.

SELECT st. text, qs.query_hash,'DBCC FREEPROCCACHE(' ,plan_handle ,')'
FROM sys .dm_exec_query_stats qs
CROSS APPLY sys .dm_exec_sql_text( qs. sql_handle) st
WHERE st. text LIKE 'SELECT * FROM Person.Address%' -- your query

There is full example in the Books Online, so you might want to read the following link:

Use DBCC FREEPROCCACHE to clear the plan cache carefully. Freeing the plan cache causes, for example, a stored procedure to be recompiled instead of reused from the cache. This can cause a sudden, temporary decrease in query performance. For each cleared cachestore in the plan cache, the SQL Server error log will contain the following informational message: "SQL Server has encountered %d occurrence(s) of cachestore flush for the ‘%s’ cachestore (part of plan cache) due to ‘DBCC FREEPROCCACHE’ or ‘DBCC FREESYSTEMCACHE’ operations." This message is logged every five minutes as long as the cache is flushed within that time interval.

You can also clear all the plans for one particular database from cache. You can use the command:


In the next post I will talk about how to force a specific execution plan.
I know that it’s a old subject, but I still see many people asking about it in the SQL Server community.

Default trace security auditing [SQL Server]

The Default trace enabled can provides us valuable information about the running server, but it isn’t well-documented.

What is the default trace? The default trace is enabled by default in SQL Server and is a minimum weight trace which consists by default of five trace files ( .trc) located in the SQL Server installation directory. The files are rolled over as time passes.

The script below will give you the most recently manipulated objects in your databases.

SELECT  TE. name ,
        v .subclass_name ,
        DB_NAME(t .DatabaseId) AS DBName ,
        T .NTDomainName ,
        t .NTUserName ,
        t .HostName ,
        t .ApplicationName ,
        t .LoginName ,
        t .Duration ,
        t .StartTime ,
        t .ObjectName ,
        CASE t. ObjectType
          WHEN 8259 THEN 'Check Constraint'
          WHEN 8260 THEN 'Default (constraint or standalone)'
          WHEN 8262 THEN 'Foreign-key Constraint'
          WHEN 8272 THEN 'Stored Procedure'
          WHEN 8274 THEN 'Rule'
          WHEN 8275 THEN 'System Table'
          WHEN 8276 THEN 'Trigger on Server'
          WHEN 8277 THEN '(User-defined) Table'
          WHEN 8278 THEN 'View'
          WHEN 8280 THEN 'Extended Stored Procedure'
          WHEN 16724 THEN 'CLR Trigger'
          WHEN 16964 THEN 'Database'
          WHEN 16975 THEN 'Object'
          WHEN 17222 THEN 'FullText Catalog'
          WHEN 17232 THEN 'CLR Stored Procedure'
          WHEN 17235 THEN 'Schema'
          WHEN 17475 THEN 'Credential'
          WHEN 17491 THEN 'DDL Event'
          WHEN 17741 THEN 'Management Event'
          WHEN 17747 THEN 'Security Event'
          WHEN 17749 THEN 'User Event'
          WHEN 17985 THEN 'CLR Aggregate Function'
          WHEN 17993 THEN 'Inline Table-valued SQL Function'
          WHEN 18000 THEN 'Partition Function'
          WHEN 18002 THEN 'Replication Filter Procedure'
          WHEN 18004 THEN 'Table-valued SQL Function'
          WHEN 18259 THEN 'Server Role'
          WHEN 18263 THEN 'Microsoft Windows Group'
          WHEN 19265 THEN 'Asymmetric Key'
          WHEN 19277 THEN 'Master Key'
          WHEN 19280 THEN 'Primary Key'
          WHEN 19283 THEN 'ObfusKey'
          WHEN 19521 THEN 'Asymmetric Key Login'
          WHEN 19523 THEN 'Certificate Login'
          WHEN 19538 THEN 'Role'
          WHEN 19539 THEN 'SQL Login'
          WHEN 19543 THEN 'Windows Login'
          WHEN 20034 THEN 'Remote Service Binding'
          WHEN 20036 THEN 'Event Notification on Database'
          WHEN 20037 THEN 'Event Notification'
          WHEN 20038 THEN 'Scalar SQL Function'
          WHEN 20047 THEN 'Event Notification on Object'
          WHEN 20051 THEN 'Synonym'
          WHEN 20549 THEN 'End Point'
          WHEN 20801 THEN 'Adhoc Queries which may be cached'
          WHEN 20816 THEN 'Prepared Queries which may be cached'
          WHEN 20819 THEN 'Service Broker Service Queue'
          WHEN 20821 THEN 'Unique Constraint'
          WHEN 21057 THEN 'Application Role'
          WHEN 21059 THEN 'Certificate'
          WHEN 21075 THEN 'Server'
          WHEN 21076 THEN 'Transact-SQL Trigger'
          WHEN 21313 THEN 'Assembly'
          WHEN 21318 THEN 'CLR Scalar Function'
          WHEN 21321 THEN 'Inline scalar SQL Function'
          WHEN 21328 THEN 'Partition Scheme'
          WHEN 21333 THEN 'User'
          WHEN 21571 THEN 'Service Broker Service Contract'
          WHEN 21572 THEN 'Trigger on Database'
          WHEN 21574 THEN 'CLR Table-valued Function'
          WHEN 21577
          THEN 'Internal Table (For example, XML Node Table, Queue Table.)'
          WHEN 21581 THEN 'Service Broker Message Type'
          WHEN 21586 THEN 'Service Broker Route'
          WHEN 21587 THEN 'Statistics'
          WHEN 21825 THEN 'User'
          WHEN 21827 THEN 'User'
          WHEN 21831 THEN 'User'
          WHEN 21843 THEN 'User'
          WHEN 21847 THEN 'User'
          WHEN 22099 THEN 'Service Broker Service'
          WHEN 22601 THEN 'Index'
          WHEN 22604 THEN 'Certificate Login'
          WHEN 22611 THEN 'XMLSchema'
          WHEN 22868 THEN 'Type'
          ELSE 'Hmmm???'
        END AS ObjectType
FROM    [fn_trace_gettable]( CONVERT(VARCHAR (150), ( SELECT TOP 1
                                                    FROM    [fn_trace_getinfo](NULL)
                                                    WHERE   [property] = 2
                                                  )), DEFAULT ) T
        JOIN sys .trace_events TE ON T. EventClass = TE .trace_event_id
        JOIN sys .trace_subclass_values v ON v. trace_event_id = TE .trace_event_id
                                            AND v. subclass_value = t .EventSubClass
WHERE IN ( 'Object:Created', 'Object:Deleted', 'Object:Altered' )AND
                -- filter statistics created by SQL server                                        
        --t.ObjectType NOT IN ( 21587 )-- filter tempdb objects
         DatabaseID <> 2
              -- AND NTUserName <> 'username'
              -- get only events in the past 24 hours
        AND StartTime > DATEADD(HH, -24, GETDATE())
ORDER BY t.StartTime DESC ;

If you need to enable:

sp_configure 'show advanced options', 1;
sp_configure 'default trace enabled', 1;

I hope this was useful.

Alert – Databases do not have Transaction log backups

The SP below sends alert when there are no transaction log backups in the last 90 minutes.

CREATE PROCEDURE [dbo].[usp_NoTlogBackup] (@Length INT=90) -- 90 Minutes
DECLARE @BadDatabases VARCHAR(8000)

SELECT @BadDatabases = STUFF(
(select ', ' + cast(a.database_name as varchar(100))
 select [name] as database_name
 from master.dbo.sysdatabases
 where databasepropertyex([name], 'recovery') in ('FULL','BULK_LOGGED') 
 and databasepropertyex([name], 'isinstandby') = 0
 and databasepropertyex([name], 'status') = 'online'
 and databasepropertyex([name], 'updateability') = 'read_write'
 and [name] not in ('model','tempdb')
 ) a
 left join msdb.dbo.backupset b
 on a.database_name = b.database_name 
 and b.type='L' 
 and datediff(hour,b.backup_finish_date,getdate()) < @Length
 where b.database_name is null

IF (@BadDatabases IS NOT NULL)

declare @ServerT varchar(100)
select @ServerT = 'Alert Backup - '+@@SERVERNAME

SET @Body = 'On ' + @@SERVERNAME + ' The following Databases do not have Transaction log backups: ' + @BadDatabases

 EXEC msdb . dbo. sp_send_dbmail        
      @recipients=N';' ,
      @body = @Body ,         
      @subject = @ServerT,         
      @profile_name ='profile_name',         
      @body_format = 'HTML'


How to list all objects and indexes [SQL Server]

Today I had to list which objects belongs to which filegroup.
It’s a simple and useful script that you can take from system catalogues: sys.filegroups, sys.indexes, sys.database_files and sys.data_spaces.

SELECT Object_name(i.[object_id]) AS [ObjectName],
       i.[index_id]               AS [IndexID],
       i.[name]                   AS [IndexName],
       i.[type_desc]              AS [IndexType],
       f.[name]                   AS [FileGroup],
       d.[physical_name]          AS [DatabaseFileName]
FROM   [sys].[indexes] i
       LEFT JOIN sys.partition_schemes pf
              ON pf.[data_space_id] = i.[data_space_id]
       LEFT JOIN [sys].[filegroups] f
              ON f.[data_space_id] = i.[data_space_id]
       LEFT JOIN [sys].[database_files] d
              ON f.[data_space_id] = d.[data_space_id]
       LEFT JOIN [sys].[data_spaces] s
              ON f.[data_space_id] = s.[data_space_id]
WHERE  Objectproperty(i.[object_id], 'IsUserTable') = 1
ORDER  BY Object_name(i.[object_id]),

Take a look this sample


In the next post I’m going to share How Move Index to other FileGroup.