How many max connections does SQL Server allows.

To find this information we can use @@MAX_CONNECTIONS global variable.

@@MAX_CONNECTIONS in SQL Server returns maximum number of simultaneous user connections allowed. Maximum user connections allowed by SQL Server by default is 32,767; this number also depends on application and server hardware limits. This cam also be configured at server-level to avoid too many connections.

@@CONNECTIONS returns number of connection attempts (successful/failed) made to SQL Server since SQL Server is started. Since this include all attempts it can be greater than @@MAX_CONNECTIONS.

SELECT [ConnectionAttempts] = @@CONNECTIONS

        ,[MaximumAllowed] = @@MAX_CONNECTIONS

SQL Server - How to find domain name of SQL Instance installed using SQL query

The below script is very useful to find the domain details of SQL Instance installed 

specially if you don't have access to RDP the server.

DECLARE @Domain VARCHAR(100)
 ,@key VARCHAR(100)

SET @key = 'SYSTEM\ControlSet001\Services\Tcpip\Parameters\'

EXEC master..xp_regread @rootkey = 'HKEY_LOCAL_MACHINE'
 ,@key = @key
 ,@value_name = 'Domain'
 ,@value = @Domain OUTPUT

SELECT @@servername [SQL Instance Name]
 ,convert(VARCHAR(100), @Domain) AS [DomainName]
 ,'10.170.201.206' IPAddress

How to avoid blockings with read committed snapshot on at DB level in SQL Server

 if you are having problem with blocking between readers (SELECT) and writers (INSERT/UPDATE/DELETE), then you can enable this property without changing anything from the application. Which means application would still run under read committed isolation and will still read only committed data.

ALTER DATABASE <DB_NAME> SET READ_COMMITTED_SNAPSHOT ON WITH ROLLBACK IMMEDIATE

SQL Server 2005 on wards, SQL engine provides only one new isolation level and an optimistic implementation of READ COMMITTED. Isolation level SNAPSHOT is a new isolation level and READ COMMITTED SNAPSHOT is the same isolation level as READ COMMITTED but is the optimistic implementation of it.

Find Memory used and free space in GBs in SQL Server

The below SQL Script will help you to identify how much memory consumed by SQL Sessions and memory free for the max memory allocated to SQL Instance

SET NOCOUNT ON;
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
SET LOCK_TIMEOUT 10000;

DECLARE @ServiceName NVARCHAR(100)

SET @ServiceName = CASE WHEN @@SERVICENAME = 'MSSQLSERVER' T

HEN 'SQLServer:' ELSE 'MSSQL$' + @@SERVICENAME + ':' END

DECLARE @Perf TABLE (
 object_name NVARCHAR(20)
 ,counter_name NVARCHAR(128)
 ,instance_name NVARCHAR(128)
 ,cntr_value BIGINT
 ,formatted_value NUMERIC(20, 2)
 ,shortname NVARCHAR(20)
 )

INSERT INTO @Perf (
 object_name
 ,counter_name
 ,instance_name
 ,cntr_value
 ,formatted_value
 ,shortname
 )
SELECT CASE WHEN CHARINDEX('Memory Manager', object_name) > 0 

THEN 'Memory Manager' WHEN CHARINDEX('Buffer Manager', object_name) > 0 

THEN 'Buffer Manager' WHEN CHARINDEX('Plan Cache', object_name) > 0 

THEN 'Plan Cache' WHEN CHARINDEX('Buffer Node', object_name) > 0 THEN 'Buffer Node' -- 2008
  WHEN CHARINDEX('Memory Node', object_name) > 0 THEN 'Memory Node' -- 2012
  WHEN CHARINDEX('Cursor', object_name) > 0 THEN 'Cursor' ELSE NULL END AS object_name
 ,CAST(RTRIM(counter_name) AS NVARCHAR(100)) AS counter_name
 ,RTRIM(instance_name) AS instance_name
 ,cntr_value
 ,CAST(NULL AS DECIMAL(20, 2)) AS formatted_value
 ,SUBSTRING(counter_name, 1, PATINDEX('% %', counter_name)) shortname
FROM sys.dm_os_performance_counters
WHERE (
  object_name LIKE @ServiceName + 'Buffer Node%' 

-- LIKE is faster than =. I have no idea why
  OR object_name LIKE @ServiceName + 'Buffer Manager%'
  OR object_name LIKE @ServiceName + 'Memory Node%'
  OR object_name LIKE @ServiceName + 'Plan Cache%'
  )
 AND (
  counter_name LIKE '%pages %'
  OR counter_name LIKE '%Node Memory (KB)%'
  OR counter_name = 'Page life expectancy'
  )
 OR (
  object_name = @ServiceName + 'Memory Manager'
  AND counter_name IN (
   'Granted Workspace Memory (KB)'
   ,'Maximum Workspace Memory (KB)'
   ,'Memory Grants Outstanding'
   ,'Memory Grants Pending'
   ,'Target Server Memory (KB)'
   ,'Total Server Memory (KB)'
   ,'Connection Memory (KB)'
   ,'Lock Memory (KB)'
   ,'Optimizer Memory (KB)'
   ,'SQL Cache Memory (KB)'
   ,
   -- for 2012
   'Free Memory (KB)'
   ,'Reserved Server Memory (KB)'
   ,'Database Cache Memory (KB)'
   ,'Stolen Server Memory (KB)'
   )
  )
 OR (
  object_name LIKE @ServiceName + 'Cursor Manager by Type%'
  AND counter_name = 'Cursor memory usage'
  AND instance_name = '_Total'
  )

-- Add unit to 'Cursor memory usage'
UPDATE @Perf
SET counter_name = counter_name + ' (KB)'
WHERE counter_name = 'Cursor memory usage'

-- Convert values from pages and KB to MB and rename counters accordingly
UPDATE @Perf
SET 

counter_name = REPLACE(REPLACE(REPLACE(counter_name, ' pages', ''), 

' (KB)', ''), ' (MB)', '')
,formatted_value = CASE WHEN counter_name LIKE '%pages' THEN cntr_value / 128.

 WHEN counter_name LIKE '%(KB)' THEN cntr_value / 1024. ELSE cntr_value END

-- Delete some pre 2012 counters for 2012 in order to remove duplicates
DELETE P2008
FROM @Perf P2008
INNER JOIN @Perf P2012 ON 

REPLACE(P2008.object_name, 'Buffer', 'Memory') = P2012.object_name
 AND P2008.shortname = P2012.shortname
WHERE P2008.object_name IN (
  'Buffer Manager'
  ,'Buffer Node'
  )

-- Update counter/object names so they look like in 2012
UPDATE PC
SET object_name = REPLACE(object_name, 'Buffer', 'Memory')
 ,counter_name = ISNULL(M.NewName, counter_name)
FROM @Perf PC
LEFT JOIN (
 SELECT 'Free' AS OldName
  ,'Free Memory' AS NewName
 
 UNION ALL
 
 SELECT 'Database'
  ,'Database Cache Memory'
 
 UNION ALL
 
 SELECT 'Stolen'
  ,'Stolen Server Memory'
 
 UNION ALL
 
 SELECT 'Reserved'
  ,'Reserved Server Memory'
 
 UNION ALL
 
 SELECT 'Foreign'
  ,'Foreign Node Memory'
 ) M ON M.OldName = PC.counter_name
 AND NewName NOT IN (
  SELECT counter_name
  FROM @Perf
  WHERE object_name = 'Memory Manager'
  )
WHERE object_name IN (
  'Buffer Manager'
  ,'Buffer Node'
  )

-- Build Memory Tree
DECLARE @MemTree TABLE (
 Id INT
 ,ParentId INT
 ,counter_name NVARCHAR(128)
 ,formatted_value NUMERIC(20, 2)
 ,shortname NVARCHAR(20)
 )

-- Level 5
INSERT @MemTree (
 Id
 ,ParentId
 ,counter_name
 ,formatted_value
 ,shortname
 )
SELECT Id = 1226
 ,ParentId = 1225
 ,instance_name AS counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Plan Cache'
 AND counter_name IN ('Cache')
 AND instance_name <> '_Total'

-- Level 4
INSERT @MemTree (
 Id
 ,ParentId
 ,counter_name
 ,formatted_value
 ,shortname
 )
SELECT Id = 1225
 ,ParentId = 1220
 ,'Plan ' + counter_name AS counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Plan Cache'
 AND counter_name IN ('Cache')
 AND instance_name = '_Total'

UNION ALL

SELECT Id = 1222
 ,ParentId = 1220
 ,counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Cursor'
 OR (
  object_name = 'Memory Manager'
  AND shortname IN (
   'Connection'
   ,'Lock'
   ,'Optimizer'
   ,'SQL'
   )
  )

UNION ALL

SELECT Id = 1112
 ,ParentId = 1110
 ,counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Memory Manager'
 AND shortname IN ('Reserved')

UNION ALL

SELECT Id = P.ParentID + 1
 ,ParentID = P.ParentID
 ,'Used Workspace Memory' AS counter_name
 ,SUM(used_memory_kb) / 1024. AS formatted_value
 ,NULL AS shortname
FROM sys.dm_exec_query_resource_semaphores
CROSS JOIN (
 SELECT 1220 AS ParentID
 
 UNION ALL
 
 SELECT 1110
 ) P
GROUP BY P.ParentID

-- Level 3
INSERT @MemTree (
 Id
 ,ParentId
 ,counter_name
 ,formatted_value
 ,shortname
 )
SELECT Id = CASE counter_name WHEN 'Granted Workspace Memory' 

THEN 1110 WHEN 'Stolen Server Memory' THEN 1220 ELSE 1210 END
 ,ParentId = CASE counter_name WHEN 'Granted Workspace Memory'

 THEN 1100 ELSE 1200 END
 ,counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Memory Manager'
 AND counter_name IN (
  'Stolen Server Memory'
  ,'Database Cache Memory'
  ,'Free Memory'
  ,'Granted Workspace Memory'
  )

-- Level 2
INSERT @MemTree (
 Id
 ,ParentId
 ,counter_name
 ,formatted_value
 ,shortname
 )
SELECT Id = CASE WHEN counter_name = 'Maximum Workspace Memory' 

THEN 1100 ELSE 1200 END
 ,ParentId = 1000
 ,counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Memory Manager'
 AND counter_name IN (
  'Total Server Memory'
  ,'Maximum Workspace Memory'
  )

-- Level 1
INSERT @MemTree (
 Id
 ,ParentId
 ,counter_name
 ,formatted_value
 ,shortname
 )
SELECT Id = 1000
 ,ParentId = NULL
 ,counter_name
 ,formatted_value
 ,shortname
FROM @Perf
WHERE object_name = 'Memory Manager'
 AND counter_name IN ('Target Server Memory')

-- Level 4 -- 

'Other Stolen Server Memory' = 

'Stolen Server Memory' - SUM(Children of 'Stolen Server Memory')
INSERT @MemTree (
 Id
 ,ParentId
 ,counter_name
 ,formatted_value
 ,shortname
 )
SELECT Id = 1222
 ,ParentId = 1220
 ,counter_name = '<Other Memory Clerks>'
 ,formatted_value = (
  SELECT SSM.formatted_value
  FROM @MemTree SSM
  WHERE Id = 1220
  ) - SUM(formatted_value)
 ,shortname = 'Other Stolen'
FROM @MemTree
WHERE ParentId = 1220

-- Results:
-- PLE and Memory Grants
SELECT [Counter Name] = 

P.counter_name + ISNULL(' (Node: ' + NULLIF(P.instance_name, '') + ')', '')
 ,cntr_value AS Value
 ,RecommendedMinimum = CASE WHEN P.counter_name = 'Page life expectancy'
   AND R.Value <= 300 -- no less than 300
   THEN 300 WHEN P.counter_name = 'Page life expectancy'
   AND R.Value > 300 THEN R.Value ELSE NULL END
FROM @Perf P
LEFT JOIN -- Recommended PLE calculations
 (
 SELECT object_name
  ,counter_name
  ,instance_name
  ,CEILING(formatted_value / 4096. * 5) * 60 AS Value 

-- 300 per every 4GB of Buffer Pool memory or around 60 seconds (1 minute) per every 819MB
 FROM @Perf PD
 WHERE counter_name = 'Database Cache Memory'
 ) R ON R.object_name = P.object_name
 AND R.instance_name = P.instance_name
WHERE (
  P.object_name = 'Memory Manager'
  AND P.counter_name IN (
   'Memory Grants Outstanding'
   ,'Memory Grants Pending'
   ,'Page life expectancy'
   )
  )
 OR -- For NUMA
 (
  P.object_name = 'Memory Node'
  AND P.counter_name = 'Page life expectancy'
  AND (
   SELECT COUNT(DISTINCT instance_name)
   FROM @Perf
   WHERE object_name = 'Memory Node'
   ) > 1
  )
ORDER BY P.counter_name DESC
 ,P.instance_name

-- Get physical memory
-- You can also extract this information from sys.dm_os_sys_info 

but the column names have changed starting from 2012
IF OBJECT_ID('tempdb..#msver') IS NOT NULL
 DROP TABLE #msver

CREATE TABLE #msver (
 ID INT
 ,Name SYSNAME
 ,Internal_Value INT
 ,Value NVARCHAR(512)
 )

INSERT #msver
EXEC master.dbo.xp_msver 'PhysicalMemory'

-- Physical memory, config parameters and Target memory
SELECT min_server_mb = (
  SELECT CAST(value_in_use AS DECIMAL(20, 2))
  FROM sys.configurations
  WHERE name = 'min server memory (MB)'
  )
 ,max_server_mb = (
  SELECT CAST(value_in_use AS DECIMAL(20, 2))
  FROM sys.configurations
  WHERE name = 'max server memory (MB)'
  )
 ,target_mb = (
  SELECT formatted_value
  FROM @Perf
  WHERE object_name = 'Memory Manager'
   AND counter_name IN ('Target Server Memory')
  )
 ,physical_mb = CAST(Internal_Value AS DECIMAL(20, 2))
FROM #msver
 -- Memory tree
 ;

WITH CTE
AS (
 SELECT 0 AS lvl
  ,counter_name
  ,formatted_value
  ,Id
  ,NULL AS ParentId
  ,shortname
  ,formatted_value AS TargetServerMemory
  ,CAST(NULL AS DECIMAL(20, 4)) AS Perc
  ,CAST(NULL AS DECIMAL(20, 4)) AS PercOfTarget
 FROM @MemTree
 WHERE ParentId IS NULL
 
 UNION ALL
 
 SELECT CTE.lvl + 1
  ,CAST(REPLICATE(' ', 6 * (CTE.lvl)) + NCHAR(124) + REPLICATE(NCHAR(183), 3)

 + MT.counter_name AS NVARCHAR(128))
  ,MT.formatted_value
  ,MT.Id
  ,MT.ParentId
  ,MT.shortname
  ,CTE.TargetServerMemory
  ,CAST(ISNULL(1.0 * MT.formatted_value / NULLIF(CTE.formatted_value, 0), 0) 

AS DECIMAL(20, 4)) AS Perc
  ,CAST(ISNULL(1.0 * MT.formatted_value / NULLIF(CTE.TargetServerMemory, 0), 0) 

AS DECIMAL(20, 4)) AS PercOfTarget
 FROM @MemTree MT
 INNER JOIN CTE ON MT.ParentId = CTE.Id
 )
SELECT counter_name AS [Counter Name]
 ,CASE WHEN formatted_value > 0 THEN formatted_value ELSE NULL END AS [Memory MB]
 ,Perc AS [% of Parent]
 ,CASE WHEN lvl >= 2 THEN PercOfTarget ELSE NULL END AS [% of Target]
FROM CTE
ORDER BY ISNULL(Id, 10000)
 ,formatted_value DESC;