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Archive for the ‘DBA Stuff’ Category

SQL DBA – Get top Tables with Stale Statistics

November 10, 2017 Leave a comment

 
SQL Server Query Optimizer (QO) uses Statistics to create query plans that improve query performance. The QO uses these statistics to estimate the cardinality (number of rows) in the query result.

There are times when these STATISTICS may go stale after certain INSERT, UPDATE and DELETE operations which involves large amount of rows, not qualifying for Auto-Stats Threshold.

For more about Statistics and Threshold check on MSDN Docs link
 

Identify Stale Stats:

Here is a simple query to identify TOP tables that have stale statistics, so that you can create UPDATE statistics for them explicitly:

SELECT TOP 50
	 CONCAT(sch.name, '.', obj.name) AS 'Table Name'
	,MAX(sp.last_updated)			AS 'Stats Last Updated'
	,MAX(sp.rows)					AS 'Rows'
	,MAX(sp.modification_counter)	AS 'Modification Counter'
FROM sys.stats st
JOIN sys.objects obj ON st.object_id = obj.object_id
JOIN sys.schemas sch ON obj.schema_id = sch.schema_id
CROSS APPLY sys.dm_db_stats_properties(obj.object_id, st.stats_id) AS sp
WHERE obj.is_ms_shipped = 0 
GROUP BY CONCAT(sch.name, '.', obj.name)
ORDER BY MAX(sp.modification_counter) DESC;


 

UPDATE Stats:

UPDATE STATISTICS dbo.table_name
GO

 


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Categories: DBA Stuff

SQL DBA – Query to check Status of last running SQL Jobs

July 20, 2017 Leave a comment

 
To check the status of current running jobs you can use the “Job Activity Monitor” feature in SSMS, but sometimes opening and refreshing the tool takes time.

Here is a simple query you can run in SSMS or from any custom tool to get the status of current running jobs:
 

–> Query #1: This query uses sysjobs view to get the list of all jobs and sysjobhistory view to get the latest status record.

SELECT 
	j.name AS JobName
	,CONVERT(VARCHAR,DATEADD(S,(run_time/10000)*60*60 /* hours */  
          +((run_time - (run_time/10000) * 10000)/100) * 60 /* mins */  
          + (run_time - (run_time/100) * 100)  /* secs */
           ,CONVERT(DATETIME,RTRIM(run_date),113)),100) AS RunTimeStamp
	,CASE 
		WHEN j.enabled = 1 THEN 'Enabled'  
		ELSE 'Disabled'  
	END JobStatus
	,CASE 
		WHEN jh.run_status = 0 THEN 'Failed'
		WHEN jh.run_status = 1 THEN 'Succeeded'
		WHEN jh.run_status = 2 THEN 'Retry'
		WHEN jh.run_status = 3 THEN 'Cancelled'
		ELSE 'Unknown'  
	END JobRunStatus
FROM msdb.dbo.sysjobs j
OUTER APPLY(
	SELECT TOP 1 * 
	FROM msdb.dbo.sysjobhistory jh
	WHERE jh.job_id = j.job_id AND jh.step_id = 0 
	order by jh.instance_id DESC) jh
where j.name like 'ADF%'
ORDER BY j.name, jh.run_date, jh.run_time 

 

–> Query #2; This query uses sysjobs view to get the list of all jobs and sysjobservers view to get the current status of job.

SELECT 
	j.name AS JobName
	,IIF(js.last_run_date > 0, 
		DATETIMEFROMPARTS(js.last_run_date/10000, js.last_run_date/100%100, js.last_run_date%100, 
		js.last_run_time/10000, js.last_run_time/100%100, js.last_run_time%100, 0), 
		NULL) AS RunTimeStamp
	,CASE 
		WHEN j.enabled = 1 THEN 'Enabled'  
		ELSE 'Disabled'  
	END JobStatus
	,CASE 
		WHEN js.last_run_outcome = 0 THEN 'Failed'
		WHEN js.last_run_outcome = 1 THEN 'Succeeded'
		WHEN js.last_run_outcome = 2 THEN 'Retry'
		WHEN js.last_run_outcome = 3 THEN 'Cancelled'
		ELSE 'Unknown'  
	END JobRunStatus
FROM msdb.dbo.sysjobs j
JOIN msdb.dbo.sysjobservers js on js.job_id = j.job_id
where j.name like 'ADF%'
ORDER BY j.name, js.last_run_date, js.last_run_time 

 

And if you noted in both the queries above, I’ve used different way to calculate the RunTimeStamp, first by parsing the rum_time column, second by using DateTimeFromParts() function.


Categories: DBA Stuff Tags: ,

SQL DBA – SQL Agent Job history not showing or vanishing away

July 17, 2017 Leave a comment

 
This happened when we started working on a new SQL Server instance for our DEV environment. The history of SQL jobs was not getting retained after a day or few runs.

I checked on the SQL Agent Properties and found that there are some config values set which were very low:
jobhistory_max_rows = 10000
jobhistory_max_rows_per_job = 100

So I checked on MSDN and found that the max permissible values and set them to 999999 & 49999 respectively.

–> This can also be changed by below T-SQL Query by using the system SP sp_set_sqlagent_properties:

USE [msdb]
GO

EXEC msdb.dbo.sp_set_sqlagent_properties 
	@jobhistory_max_rows=999999, 
	@jobhistory_max_rows_per_job=49999
GO

Categories: DBA Stuff Tags: ,

SQL DBA – Stop multiple running SQL Jobs at once

June 14, 2017 1 comment

 
Just like my previous post on Enable/Disable multiple SQL Jobs [link], here I will show how can we stop multiple jobs running by SQL Agent at once.

–> Although you can very well Stop a SQL Job in SSMS by simple right-clicking on it. But if you have multiple SQL Jobs running, to stop each of them will be a cumbersome and time taking task.

I will show how this can be done by a T-SQL query:

USE msdb;
GO

-- Stop Multiple running SQL Jobs at once:
DECLARE @dynSql NVARCHAR(MAX) = ''

SELECT @dynSql += N' msdb.dbo.sp_stop_job @job_name = ''' + j.name + N'''' 
			+ CHAR(10) + CHAR(13)
FROM msdb.dbo.sysjobs j
JOIN msdb.dbo.sysjobactivity AS ja 
ON ja.job_id = j.job_id
WHERE ja.start_execution_date IS NOT NULL
AND ja.stop_execution_date IS NULL
ORDER BY j.name;

PRINT @dynSql;
GO

Simply Copy-Paste the the above Dynamically generated SQL Script and Execute it, it will Stop all Running SQL Jobs at once.


Categories: DBA Stuff, SQL Tips Tags: ,

SQL DBA – Quickly Clone a Database in SQL Server (2016 SP1 & 2014 SP2) with DBCC CLONEDATABASE command

December 22, 2016 1 comment

 
Have you ever been in a similar situation where your PROD database size is in GBs or TBs, and for a code-release validation or some performance-fix you need to restore it on an Dev or Test server? You know that taking backup & restore will take lot of time, but you have no other option.

We also face this many a times as our PROD database size ranges from 500 GB to 1-2 TB, and we end up waiting 4-5 hrs in this activity.

There are even third party tools, but they also take good time and have their own pros & cons.
 

Now SQL Server brings a new feature with SQL Server 2016 SP1 & 2014 SP2, i.e. DBCC CLONEDATABASE, to create a new database clone of an existing database within seconds. The new cloned database created is ReadOnly, with no data, but with Statistics.

With DBCC CLONEDATABASE feature you can generate a clone of a database in order to investigate a performance issue related to a Query or Workload.

Note: As best practice suggested by Microsoft product team this clone Database is not supposed to remain in PROD database, but can be moved to a Dev or Test box for further troubleshooting and diagnostic purposes.
 

–> Syntax:

DBCC CLONEDATABASE (source_db_name, target_clone_db_name)
[WITH [NO_STATISTICS][,NO_QUERYSTORE]]

 

–> The above statement creates Clone of the source database in following operations:

1. Validate the source database.

2. Get S lock for the source database.

3. Create snapshot of the source database.

4. Create an empty database by inheriting from “model” database, and using the same file layout as the source but with default file sizes as the “model” database.

5. Get X lock for the clone database.

6. Copies the system metadata from the source to the destination database.

7. Copies all schema for all objects from the source to the destination database.

8. Copies statistics for all indexes from the source to the destination database.

9. Release all DB locks.
 

–> Now let’s create a Clone Database on AdvantureWorks database:

-- With Stats

DBCC CLONEDATABASE ('AdventureWorks2014', 'AdventureWorks2014_CloneDB')

Message:

Database cloning for ‘AdventureWorks2014’ has started with target as ‘AdventureWorks2014_CloneDB’.

Database cloning for ‘AdventureWorks2014’ has finished. Cloned database is ‘AdventureWorks2014_CloneDB’.

Database ‘AdventureWorks2014_CloneDB’ is a cloned database. A cloned database should be used for diagnostic purposes only and is not supported for use in a production environment.

DBCC execution completed. If DBCC printed error messages, contact your system administrator.
 

–> I’ll create one more Clone Database without Stats:

-- Without Stats

DBCC CLONEDATABASE ('AdventureWorks2014', 'AdventureWorks2014_CloneDB_No_Stats')
WITH NO_STATISTICS, NO_QUERYSTORE

dbcc-clonedatabase
 

–> Let’s check the file size of all 3 Databases:

– The 1st image shows the size of original AdventureWorks2014 database i.e. 207 MB

– And 2nd and 3rd shows the size of other two Clone Databases i.e. just 16 MB.

dbcc-clonedb-01

dbcc-clonedb-02

dbcc-clonedb-03

 

–> Now we will check the Execution Plans of a query on all these three databases:

-- Check Execution plan on below T-SQL query in all 3 databases:

SELECT 
	P.BusinessEntityID, P.Title, P.FirstName, P.MiddleName, P.LastName, 
	E.BirthDate, E.Gender, E.HireDate, E.JobTitle, E.MaritalStatus, 
	D.Name
FROM [Person].[Person] P
INNER JOIN [HumanResources].[Employee] E ON E.BusinessEntityID = P.BusinessEntityID
CROSS APPLY (
	SELECT TOP 1 DepartmentID
	FROM [HumanResources].[EmployeeDepartmentHistory] DH 
	WHERE DH.BusinessEntityID = E.BusinessEntityID 
	ORDER BY StartDate DESC) EDH
INNER JOIN [HumanResources].[Department] D ON D.DepartmentID = EDH.DepartmentID

 

– On executing the above query on original AdventureWorks2014 database & AdventureWorks2014_CloneDB it shows same execution plan, like it shows:

1. Hash Match operator
2. 72% cost on Person PK
3. 18% cost on EmployeeDepartmentHistory PK

dbcc-clonedb-04
(click on the image to expand)

– But on executing the same query on AdventureWorks2014_CloneDB_No_Stats it shows different execution plan, here it shows:

1. Nested Loop operator
2. 92% cost on Person PK
3. 5% cost on EmployeeDepartmentHistory PK

dbcc-clonedb-05
(click on the image to expand)