SP_WHO2 information

One of the first lines of defense in determining the causes of database slowdowns is to use sp_who2. sp_who2 shows all the sessions that are currently established in the database. These are denoted as Spid‘s, or Server process Id’s. Running sp_who2 is easy, all that is required is to type sp_who2 and execute it, however it’s a good idea to call it with EXEC.

EXEC sp_who2

Results of sp_who2

The first 50 results are system spids. Generally these do not effect slowdowns of the system. These system events include the Checkpoint writer, Log writers and task schedulers. User processes are SPID numbers 50 and over. In diagnosing slowdowns it is these SPIDs that are the potential resource hogs.

sp_who2 also takes a optional parameter of a SPID. If a spid is passed, then the results of sp_who2 only show the row or rows of the executing SPID.

EXEC sp_who2 243

There are four main things to look for when when diagnosing slowdowns.

1.       Blocking

2.       High CPU usage

3.       High IO usage

4.       Multiple entries for the same SPID representing parallelism.

When a number is shown in the column named BlkBy, this represents the SPID that is currently stopping the SPID in the row shown. Sometimes many rows will show SPID numbers in the BlkBy column. This is because there is a chain of blockers. The way this occurs usually starts with one "lead" blocker blocking another process. In turn, the process that is being blocked, blocks others. This occurs down a chain. It can be a messy situation. In order to rectify, you may have to kill the lead blocker. If it happens often, you will want to research why this particular process is blocking. So, before you kill any process, find out what statement it is running first. To do this, execute DBCC INPUTBUFFER(SPID).

High CPUTime or High DiskIO time is usually spotted by comparing the relative CPUTime to the DiskIO time. It should be noted that CPUTime and DiskIO time represent the sum of all executions since the SPID has been active. It may take some training before you are able to spot a high number here. At times, you will see very high CPUTimes and almost no corresponding DiskIO. This is usually indicative of a bad execution plan.

Multiple rows that have the same SPID are known as Parellel processes. This happens when SQL Server has determined that a particular query is going to take a long time to run (according to the parallel settings at the server level). When this happens, SQL Server will launch multiple threads for the same procedure. When this happens often, it can have a devastating effect on SQL Server. Particularly IO. To rectify, either raise the query threshold for parallelism or turn down the maximum processors that parallelism can use (Max DOP) Max degree of parallelism, a setting at the server level.

Temp DB size and Growth parameters

You can view the size and file growth parameters of the tempdb data or log files by using following script :

  

 

SELECT

    name AS FileName,

    size*1.0/128 AS FileSizeinMB,

    CASE max_size

        WHEN 0 THEN 'Autogrowth is off.'

        WHEN -1 THEN 'Autogrowth is on.'

        ELSE 'Log file will grow to a maximum size of 2 TB.'

    END,

    growth AS 'GrowthValue',

    'GrowthIncrement' =

        CASE

            WHEN growth = 0 THEN 'Size is fixed and will not grow.'

            WHEN growth > 0 AND is_percent_growth = 0

                THEN 'Growth value is in 8-KB pages.'

            ELSE 'Growth value is a percentage.'

        END

FROM tempdb.sys.database_files;

GO

I hope this will helps you all

 

Tempd DB resize (modify size) using script

use master
 go

 alter database tempdb modify file
  (name = tempdev,
  size = 8192MB,
  maxsize = 10241MB,
  filegrowth = 2048MB)
 go

 

 alter database tempdb modify file
  (name = templog,
  size = 512MB,
  maxsize = 1025MB,
  filegrowth = 256MB)
 go
 checkpoint
 go

Checkpoint operations

 

Factors Affecting the Duration of Checkpoint Operations

 

In general, the amount time required for a checkpoint operation increases with the number of dirty pages that the operation must write. By default, to minimize the performance impact on other applications, SQL Server adjusts the frequency of writes that a checkpoint operation performs. Decreasing the write frequency increases the time the checkpoint operation requires to complete. SQL Server uses this strategy for a manual checkpoint unless a checkpoint_duration value is specified in the CHECKPOINT command.

The performance impact of using checkpoint_duration depends on the number of dirty pages, the activity on the system, and the actual duration specified. For example, if the checkpoint would normally complete in 120 seconds, specifying a checkpoint_duration of 45 seconds causes SQL Server to devote more resources to the checkpoint than would be assigned by default. In contrast, specifying a checkpoint_duration of 180 seconds would cause SQL Server to assign fewer resources than would be assigned by default. In general, a short checkpoint_duration will increase the resources devoted to the checkpoint, while a long checkpoint_duration will reduce the resources devoted to the checkpoint. SQL Server always completes a checkpoint if possible, and the CHECKPOINT statement returns immediately when a checkpoint completes. Therefore, in some cases, a checkpoint may complete sooner than the specified duration or may run longer than the specified duration.

 

Checkpoint

For performance reasons, the Database Engine performs modifications to database pages in memory—in the buffer cache—and does not write these pages to disk after every change. Rather, the Database Engine periodically issues a checkpoint on each database. A checkpoint writes the current in-memory modified pages (known as dirty pages) and transaction log information from memory to disk and, also, records information about the transaction log.

The Database Engine supports several types of checkpoints: automatic, indirect, manual, and internal. The following table summarizes the types of checkpoints


Automatic: EXEC sp_configure 'recovery interval','seconds'
Description: Issued automatically in the background to meet the upper time limit suggested by the recovery interval server configuration option. Automatic checkpoints run to completion. Automatic checkpoints are throttled based on the number of outstanding writes and whether the Database Engine detects an increase in write latency above 20 milliseconds.


Indirect: ALTER DATABASE … SET TARGET_RECOVERY_TIME =target_recovery_time{ SECONDS | MINUTES }
Description: Issued in the background to meet a user-specified target recovery time for a given database. The default target recovery time is 0, which causes automatic checkpoint heuristics to be used on the database. If you have used ALTER DATABASE to set TARGET_RECOVERY_TIME to >0, this value is used, rather than the recovery interval specified for the server instance.


Manual: CHECKPOINT [ checkpoint_duration ]
Description: Issued when you execute a Transact-SQL CHECKPOINT command. The manual checkpoint occurs in the current database for your connection. By default, manual checkpoints run to completion. Throttling works the same way as for automatic checkpoints. Optionally, the checkpoint_durationparameter specifies a requested amount of time, in seconds, for the checkpoint to complete.


Internal: None
Description: Issued by various server operations such as backup and database-snapshot creation to guarantee that disk images match the current state of the log.

Sql server database states

 In sql server database having several states. The following are the database states.

ONLINE State :

          Database is available for access. The primary filegroup is online, although the undo phase of recovery may not have been completed.


OFFLINE State :

        Database is unavailable. A database becomes offline by explicit user action and remains offline until additional user action is taken. For example, the database may be taken offline in order to move a file to a new disk. The database is then brought back online after the move has been completed.

 
RESTORING State :

          One or more files of the primary filegroup are being restored, or one or more secondary files are being restored offline. The database is unavailable.

 
RECOVERING State :

          Database is being recovered. The recovering process is a transient state; the database will automatically become online if the recovery succeeds. If the recovery fails, the database will become suspect. The database is unavailable.

 
RECOVERY PENDING State :

            Database is being recovered. The recovering process is a transient state; the database will automatically become online if the recovery succeeds. If the recovery fails, the database will become suspect. The database is unavailable.

 
SUSPECT State :

           SQL Server has encountered a resource-related error during recovery. The database is not damaged, but files may be missing or system resource limitations may be preventing it from starting. The database is unavailable. Additional action by the user is required to resolve the error and let the recovery process be completed

 
EMERGENCY State :

        At least the primary filegroup is suspect and may be damaged. The database cannot be recovered during startup of SQL Server. The database is unavailable. Additional action by the user is required to resolve the problem.

 

 


I hope this article is useful to all users.

Modified fix orphaned users script

I modified this script to handle the 'dbo' user. So yo no longer have to run sp_changedbowner 'sa' before (Or after) running this proc.

/*************************************************************************************
This procedure should be created in the Master database. This procedure takes no
parameters. It will remap orphaned users in the current database to EXISTING logins
of the same name. This is usefull in the case a new database is created by restoring
a backup to a new database, or by attaching the datafiles to a new server.
*************************************************************************************/

IF OBJECT_ID('dbo.sp_fixusers') IS NOT NULL
BEGIN
DROP PROCEDURE dbo.sp_fixusers
IF OBJECT_ID('dbo.sp_fixusers') IS NOT NULL
PRINT '<<< FAILED DROPPING PROCEDURE dbo.sp_fixusers >>>'
ELSE
PRINT '<<< DROPPED PROCEDURE dbo.sp_fixusers >>>'
END
GO
CREATE PROCEDURE dbo.sp_fixusers
AS
BEGIN
DECLARE @username varchar(25)
DECLARE fixusers CURSOR
FOR
SELECT UserName = name FROM sysusers
WHERE issqluser = 1 and (sid is not null and sid <> 0x0)
and suser_sname(sid) is null
ORDER BY name
OPEN fixusers
FETCH NEXT FROM fixusers
INTO @username
WHILE @@FETCH_STATUS = 0
BEGIN
IF @username='dbo'
BEGIN
EXEC sp_changedbowner 'sa'
END
ELSE
BEGIN
EXEC sp_change_users_login 'update_one', @username, @username
END
FETCH NEXT FROM fixusers
INTO @username
END

CLOSE fixusers
DEALLOCATE fixusers
END
go
IF OBJECT_ID('dbo.sp_fixusers') IS NOT NULL
PRINT '<<< CREATED PROCEDURE dbo.sp_fixusers >>>'
ELSE
PRINT '<<< FAILED CREATING PROCEDURE dbo.sp_fixusers >>>'
go