Getting information about referenced and referencing tables

At times we do need to carry out some tasks related to figure out certain information about references among some database objects. Today's post is going to show an example for tables by using T-SQL. There are two SQL Server system views we will use to query that information, they are 'sys.objects' and 'sys.sysreferences'. The view 'sys.objects' contains information for each database object (DDL and DML triggers) created inside of a particular user schema, and sys.sysreferences has the following important columns which will give us the object id of the referenced and referencing object.

• rkeyid: Contains the ID of the object which is being referenced.
• fkeyid: Contains the ID of the object which is referencing.  

For instance, now we are going to figure out which tables are being referenced from the 'Product' table inside the 'AdventureWorks' database:

SELECT S.[name] AS 'Referenced Table'
FROM sys.objects S INNER JOIN sys.sysreferences R 
   ON S.OBJECT_ID = R.rkeyid
WHERE S.[type] = 'U' AND R.fkeyid = OBJECT_ID('[Production].[Product]')

Having done that, we can also figure out which tables are referencing to the 'Product' table. 

SELECT S.[name] AS 'Referencing Table'
FROM sys.objects S INNER JOIN sys.sysreferences R 
   ON S.OBJECT_ID = R.fkeyid
WHERE S.[type] = 'U' AND R.fkeyid = OBJECT_ID('[Production].[Product]')

As I said earlier, not only can we use those views for tables, but also for other objects like functions, stored procedures, views, etc. I hope you can make the most out of this tip. Let me know any remarks you may have. Stay tuned.

Purging old backup files by using forfiles windows tool

It is well know that most backup strategies include a step to purge backup files to keep the most recent backups in the database server so that the disk space can be used properly. It is of paramount importance to schedule this task inside a SQL job in order to avoid running out of space. Today I am going to share a script to do that that uses forfiles windows tool via cmdshell. This script is within a stored procedure which has some input paramaters such as the database name, backup type, drive, and retention days.

USE [master] 
GO
CREATE PROCEDURE [dbo].[sp_DBA_Backup_FilesCleanup] (
@DatabaseName VARCHAR(200),
@BackupType VARCHAR(100),
@DriveName VARCHAR(1), 
@RetentionDays VARCHAR(4))
WITH ENCRYPTION
AS 
BEGIN
    SET NOCOUNT ON

    DECLARE @strcmd VARCHAR(4000)
    DECLARE @directory VARCHAR(4000)
    
    SET @directory=@DriveName + ':\SQLBackup\' + @DatabaseName --+ '\'  + @BackupType 
    SET @strcmd='forfiles /p "'+@directory+'" /s /d -'+ @RetentionDays +' /c "cmd /c del /q @path"'
      -- print @strcmd
    EXEC master.dbo.xp_cmdshell   @strcmd 
   
   SET NOCOUNT OFF
END
GO

The logic deletes old backups files located on a path with this pattern '<Drive>:\<BackupDirectory>\<DatabaseName>\<BackupType>'. For instance, if we want to delete Full + Diff + Log Backup Files of the database 'MyDB' older than one week and supposing that those backups files are located on the drive 'G' then the full path would be 'G:\SQLBackup\MyDB\Full' for Full Backups, 'G:\SQLBackup\MyDB\Diff' for Differential Backups, and 'G:\SQLBackup\MyDB\Log' for Log Backups. So, using the following stored procedure and according to the example above, we should execute it with the following parameters:

USE [master] 
GO
EXEC dbo.sp_DBA_Backup_FilesCleanup  @DatabaseName='MyDB' , @BackupType='FULL',@DriveName='G', @RetentionDays='7'
GO
EXEC dbo.sp_DBA_Backup_FilesCleanup  @DatabaseName='MyDB' , @BackupType='Diff',@DriveName='G', @RetentionDays='7'
GO
EXEC dbo.sp_DBA_Backup_FilesCleanup  @DatabaseName='MyDB' , @BackupType='Log',@DriveName='G', @RetentionDays='7'

That is all for now. Let me know any remarks you may have. Stay tuned.

Getting useful information of data & log files for all databases

It is a common DBA task to check the unused space of all database files in order to make the decision of extending the file sizes and provide them with more disk hard space in the likely event of running out of it. Today I have two scripts I would like to share with you to get that info easily. The first one is to report some very important information about every data & log file for all databases such as name, file size in GB, space used in GB, free space in GB and percentage, growth settings in tandem with other information at database level such as collation, compatibility level, owner, and more. Here you are:

USE master
GO
IF EXISTS (SELECT name FROM master.sys.tables WHERE name='TmpFileSpace')
    DROP TABLE TmpFileSpace

CREATE TABLE [dbo].[TmpFileSpace](
    [DatabaseName] [nvarchar](128) NULL,
    [FileName] [sysname] NOT NULL,
    [FileSizeGB] [decimal](10, 2) NULL,
    [SpaceUsedGB] [decimal](10, 1) NULL,
    [SpaceFreeGB] [decimal](10, 1) NULL,
    [SpaceFree%] [decimal](10, 1) NULL
) ON [PRIMARY]
 
EXEC sp_MSforeachdb '
USE [?]
INSERT INTO master.dbo.[TmpFileSpace]([DatabaseName], [FileName], [FileSizeGB], [SpaceUsedGB], [SpaceFreeGB], [SpaceFree%])
SELECT DB_NAME() DatabaseName, name FileName, 
CAST(size/128.0/1024.0 AS DECIMAL(10,2)) SizeGB, 
CAST(FILEPROPERTY(name,''SpaceUsed'') /128.0/1024.0  AS DECIMAL(10,1)) SpaceUsedGB, 
CAST((size - FILEPROPERTY(name,''SpaceUsed'')) /128.0/1024.0 AS DECIMAL(10,1)) SpaceFreeGB, 
CAST(((size - FILEPROPERTY(name,''SpaceUsed''))/(size*1.0)) *100 AS DECIMAL(10,1)) [SpaceFree%]
FROM sys.database_files'

SELECT db.name DatabaseName,db.collation_name,db.compatibility_level, SUSER_SNAME(owner_sid) OwnerName,
db.page_verify_option_desc, db.is_auto_close_on, 
db.is_auto_create_stats_on,db.is_auto_shrink_on, db.is_auto_update_stats_on,
db.is_auto_update_stats_async_on,db.name DatabaseName,  fs.FileName,
fs.FileSizeGB , fs.SpaceUsedGB, fs.SpaceFreeGB, fs.[SpaceFree%],
  physical_name, cast(size/128.0/1024.0 as decimal(10,2)) FileSizeGB,
db.state_desc,max_size,growth,is_percent_growth 
FROM sys.master_files mf
INNER JOIN sys.databases db ON mf.database_id = db.database_id
INNER JOIN TmpFileSpace FS ON mf.database_id=db_id(Fs.DatabaseName) AND mf.name=fs.FileName

DROP TABLE [TmpFileSpace]

But if you only want to get information about the size in GB, space used in GB, free space in GB of all data & log files for a specific database you can use this:

USE [YourDatabaseName]
SELECT DB_NAME() DatabaseName, name FileName, 
CAST(size/128.0/1024.0 AS DECIMAL(10,2)) SizeGB, 
CAST(FILEPROPERTY(name,'SpaceUsed') /128.0/1024.0  AS DECIMAL(10,1)) SpaceUsedGB, 
CAST((size - FILEPROPERTY(name,'SpaceUsed') ) /128.0/1024.0 AS DECIMAL(10,1)) SpaceFreeGB, 
CAST(((size - FILEPROPERTY(name,'SpaceUsed') )/(size*1.0)) *100 AS DECIMAL(10,1)) [SpaceFree%]
FROM SYS.database_files

That is all for now. Let me know any remarks you may have. 

Quickly find a cached execution plan of an Ad-Hoc query

It is clear that sometimes we just need to find a cached execution plan as quickly as possible so that it can be analysed and then use it to optimise the code in question. This work might be harder if the workload of a database server is based on ad-hoc queries because they do not reuse cached plan as good as stored procedures do especially if Ad-Hoc queries work with parameters, so in this context, we might find many cached plans for only one Ad-Hoc query and it will then make more difficult spot what we are looking for. It is of paramount importance to remember that optimisation and tuning is a never-ending task and it is worthy of our attention every so often. Today I am coming with the following script to help quickly find a cached plan execution plan for an ad-hoc query. This query filters out by the specific text you are looking for in the ad-query.

SELECT TOP 10 st.text AS [SQLText], cp.cacheobjtype CacheObjType, cp.objtype ObjType,
COALESCE(DB_NAME(st.dbid), DB_NAME(CAST(pa.value AS INT))+'*',
'Resource') AS [DatabaseName], cp.usecounts AS [PlanUsage], qp.query_plan
FROM sys.dm_exec_cached_plans cp
CROSS APPLY sys.dm_exec_sql_text(cp.plan_handle) st
CROSS APPLY sys.dm_exec_query_plan(cp.plan_handle) qp
OUTER APPLY sys.dm_exec_plan_attributes(cp.plan_handle) pa
WHERE pa.attribute = 'dbid'
AND st.text LIKE '%some text of the object or ad-hoc query%'

It well worth noting that this is why it is highly advisable using stored procedures so that CPU and memory resources can be used more efficiently. That is all for now, let me know any remarks you may have. Stay tuned.

Getting information about memory used by SQL Server

Naturally, every DBA is asked to report information about the memory used by SQL Server. Common questions are related to memory reserved and memory used currently, and sometimes we might not know how to complete this task. How many times did we take a look at the Windows Manager Task to find out that info? Many of us might have ended up quite frustrated time and time again because it did not help much. Over time Microsoft decided to provide Administrators with more useful tools and released Resource Manager tool whereby useful memory information per process is available, nevertheless, whether we want to get that info from SQL Server it might be an uphill battle as it would need that we write certain complex code at windows level.  For the time being, thinking about this situation I made the snap decision of sharing with you some helpful scripts that will alleviate the pain.

In the likely event that you might need to get the total buffer pool memory used by all databases at SQL instance level, this script is for it.

SELECT cast( cast( COUNT(*) /128.0/1024.0 as decimal(10,2)) as varchar(10)) + 'GB'  AS TotalUsageBufferPool
FROM sys.dm_os_buffer_descriptors

And if you wanted to know the buffer pool memory used by each database, you can use this:

SELECT CASE database_id 
        WHEN 32767 THEN 'ResourceDb'  ELSE db_name(database_id)         END AS DatabaseName,
        cast( COUNT(*) /128.0 as decimal(10,2)) AS [BufferPool(MB)]
FROM sys.dm_os_buffer_descriptors
GROUP BY DB_NAME(database_id) ,database_id
ORDER BY [BufferPool(MB)] DESC

Finally, and more importantly, answering the question about the total memory used by the whole SQL instance:

-- SQL2012/2014/2016/2017
select cast(cast(physical_memory_kb /1024.0/1024.0  as decimal(10,2))  as varchar(10)) + 'GB' TotalPhysicalRAM, 
cast(cast(visible_target_kb /1024.0/1024.0  as decimal(10,2)) as varchar(10)) + 'GB' MaxRAM, -- max memory configure at sql server level
cast(cast(committed_target_kb /1024.0/1024.0  as decimal(10,2)) as  varchar(10)) + 'GB' ReservedRAM,  --memory reserved
cast(cast(committed_kb /1024.0/1024.0  as decimal(10,2)) as  varchar(10)) + 'GB' UsedRAM --memory used currently
FROM sys.dm_os_sys_info

-- for SQL2005/2008/2008R2
SELECT cast(cast(physical_memory_in_bytes /1024.0/1024.0  as decimal(10,2))  as varchar(10)) + 'GB' TotalPhysicalRAM, 
cast(cast(bpool_visible /128.0/1024.0  as decimal(10,2)) as varchar(10)) + 'GB' MaxRAM, -- max memory configure at sql server level
cast(cast(bpool_commit_target /128.0/1024.0  as decimal(10,2)) as  varchar(10)) + 'GB' ReservedRAM,  --memory reserved
cast(cast(bpool_committed /128.0/1024.0  as decimal(10,2)) as  varchar(10)) + 'GB' UsedRAM --memory used currently
FROM sys.dm_os_sys_info

That is all for now. I hope you find these scripts helpful. Let me know any remarks you may have.