T-SQL Query Script to monitor Memory Usage of a SQL Server Instance

How we can monitor memory usage by a SQL Server instance ?

 -- We don't need the row count 
 SET NOCOUNT ON 
 
 -- Get size of SQL Server Page in bytes 
 DECLARE @pg_size INT, @Instancename varchar(50) 
 SELECT @pg_size = low from master..spt_values where number = 1 and type = 'E' 
 
 -- Extract perfmon counters to a temporary table 
 IF OBJECT_ID('tempdb..#perfmon_counters') is not null DROP TABLE #perfmon_counters 
 SELECT * INTO #perfmon_counters FROM sys.dm_os_performance_counters 
 
 -- Get SQL Server instance name 
 SELECT @Instancename = LEFT([object_name], (CHARINDEX(':',[object_name]))) FROM #perfmon_counters WHERE counter_name = 'Buffer cache hit ratio' 
 
 -- Print Memory usage details 
 PRINT '----------------------------------------------------------------------------------------------------' 
 PRINT 'Memory usage details for SQL Server instance ' + @@SERVERNAME + ' (' + CAST(SERVERPROPERTY('productversion') AS VARCHAR) + ' - ' + SUBSTRING(@@VERSION, CHARINDEX('X',@@VERSION),4) + ' - ' + CAST(SERVERPROPERTY('edition') AS VARCHAR) + ')' 
 PRINT '----------------------------------------------------------------------------------------------------' 
 SELECT 'Memory visible to the Operating System' 
 SELECT CEILING(physical_memory_in_bytes/1048576.0) as [Physical Memory_MB], CEILING(physical_memory_in_bytes/1073741824.0) as [Physical Memory_GB], CEILING(virtual_memory_in_bytes/1073741824.0) as [Virtual Memory GB] FROM sys.dm_os_sys_info 
 SELECT 'Buffer Pool Usage at the Moment' 
 SELECT (bpool_committed*8)/1024.0 as BPool_Committed_MB, (bpool_commit_target*8)/1024.0 as BPool_Commit_Tgt_MB,(bpool_visible*8)/1024.0 as BPool_Visible_MB FROM sys.dm_os_sys_info 
 SELECT 'Total Memory used by SQL Server Buffer Pool as reported by Perfmon counters' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Total Server Memory (KB)' 
 SELECT 'Memory needed as per current Workload for SQL Server instance' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Target Server Memory (KB)' 
 SELECT 'Total amount of dynamic memory the server is using for maintaining connections' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Connection Memory (KB)' 
 SELECT 'Total amount of dynamic memory the server is using for locks' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Lock Memory (KB)' 
 SELECT 'Total amount of dynamic memory the server is using for the dynamic SQL cache' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'SQL Cache Memory (KB)' 
 SELECT 'Total amount of dynamic memory the server is using for query optimization' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Optimizer Memory (KB) ' 
 SELECT 'Total amount of dynamic memory used for hash, sort and create index operations.' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Granted Workspace Memory (KB) ' 
 SELECT 'Total Amount of memory consumed by cursors' 
 SELECT cntr_value as Mem_KB, cntr_value/1024.0 as Mem_MB, (cntr_value/1048576.0) as Mem_GB FROM #perfmon_counters WHERE counter_name = 'Cursor memory usage' and instance_name = '_Total' 
 SELECT 'Number of pages in the buffer pool (includes database, free, and stolen).' 
 SELECT cntr_value as [8KB_Pages], (cntr_value*@pg_size)/1024.0 as Pages_in_KB, (cntr_value*@pg_size)/1048576.0 as Pages_in_MB FROM #perfmon_counters WHERE object_name= @Instancename+'Buffer Manager' and counter_name = 'Total pages' 
 SELECT 'Number of Data pages in the buffer pool' 
 SELECT cntr_value as [8KB_Pages], (cntr_value*@pg_size)/1024.0 as Pages_in_KB, (cntr_value*@pg_size)/1048576.0 as Pages_in_MB FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Database pages' 
 SELECT 'Number of Free pages in the buffer pool' 
 SELECT cntr_value as [8KB_Pages], (cntr_value*@pg_size)/1024.0 as Pages_in_KB, (cntr_value*@pg_size)/1048576.0 as Pages_in_MB FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Free pages' 
 SELECT 'Number of Reserved pages in the buffer pool' 
 SELECT cntr_value as [8KB_Pages], (cntr_value*@pg_size)/1024.0 as Pages_in_KB, (cntr_value*@pg_size)/1048576.0 as Pages_in_MB FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Reserved pages' 
 SELECT 'Number of Stolen pages in the buffer pool' 
 SELECT cntr_value as [8KB_Pages], (cntr_value*@pg_size)/1024.0 as Pages_in_KB, (cntr_value*@pg_size)/1048576.0 as Pages_in_MB FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Stolen pages' 
 SELECT 'Number of Plan Cache pages in the buffer pool' 
 SELECT cntr_value as [8KB_Pages], (cntr_value*@pg_size)/1024.0 as Pages_in_KB, (cntr_value*@pg_size)/1048576.0 as Pages_in_MB FROM #perfmon_counters WHERE object_name=@Instancename+'Plan Cache' and counter_name = 'Cache Pages' and instance_name = '_Total' 
 SELECT 'Page Life Expectancy - Number of seconds a page will stay in the buffer pool without references' 
 SELECT cntr_value as [Page Life in seconds],CASE WHEN (cntr_value > 300) THEN 'PLE is Healthy' ELSE 'PLE is not Healthy' END as 'PLE Status' FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Page life expectancy' 
 SELECT 'Number of requests per second that had to wait for a free page' 
 SELECT cntr_value as [Free list stalls/sec] FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Free list stalls/sec' 
 SELECT 'Number of pages flushed to disk/sec by a checkpoint or other operation that require all dirty pages to be flushed' 
 SELECT cntr_value as [Checkpoint pages/sec] FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Checkpoint pages/sec' 
 SELECT 'Number of buffers written per second by the buffer manager"s lazy writer' 
 SELECT cntr_value as [Lazy writes/sec] FROM #perfmon_counters WHERE object_name=@Instancename+'Buffer Manager' and counter_name = 'Lazy writes/sec' 
 SELECT 'Total number of processes waiting for a workspace memory grant' 
 SELECT cntr_value as [Memory Grants Pending] FROM #perfmon_counters WHERE object_name=@Instancename+'Memory Manager' and counter_name = 'Memory Grants Pending' 
 SELECT 'Total number of processes that have successfully acquired a workspace memory grant' 
 SELECT cntr_value as [Memory Grants Outstanding] FROM #perfmon_counters WHERE object_name=@Instancename+'Memory Manager' and counter_name = 'Memory Grants Outstanding'