SQL Server - query Page life expectancy

SELECT [object_name],
[counter_name],
[cntr_value] AS PLE -- in seconds
FROM sys.dm_os_performance_counters
WHERE [object_name] LIKE '%Manager%'
AND [counter_name] = 'Page life expectancy'

-- with formatings:
; with PLE AS
(
SELECT [object_name],
[counter_name],
[cntr_value] AS PLE, 
[cntr_value] / 86400 AS PLEDays,
[cntr_value] - (([cntr_value] / 86400) * 86400) AS PLESecondsInLastDay
FROM sys.dm_os_performance_counters
WHERE [object_name] LIKE '%Manager%'
AND [counter_name] = 'Page life expectancy'
)
SELECT [object_name], [counter_name],
PLE AS PLESec,
PLEDays,
PLESecondsInLastDay, PLESecondsInLastDay / 60,
( RIGHT('0' + CAST(PLESecondsInLastDay / 3600 AS VARCHAR),2) + ':' +
RIGHT('0' + CAST((PLESecondsInLastDay / 60) % 60 AS VARCHAR),2) + ':' +
RIGHT('0' + CAST(PLESecondsInLastDay % 60 AS VARCHAR),2)
) AS PLEInLastDay,
CAST(PLEDays AS VARCHAR) + 'd ' + 
( RIGHT('0' + CAST(PLESecondsInLastDay / 3600 AS VARCHAR),2) + ':' +
RIGHT('0' + CAST((PLESecondsInLastDay / 60) % 60 AS VARCHAR),2) + ':' +
RIGHT('0' + CAST(PLESecondsInLastDay % 60 AS VARCHAR),2)
) PLENiceFormat
FROM PLE;

SQL Server - select buffer cache usage

-- buffer cache usage per database
SELECT d.database_id,
d.name AS database_name,
COUNT(*) * 8 / 1024 AS mb_used
FROM sys.dm_os_buffer_descriptors osb
INNER JOIN sys.databases d ON d.database_id = osb.database_id
GROUP BY d.database_id, d.name
ORDER BY COUNT(*) DESC;

-- buffer cache usage for whole instance
SELECT COUNT(*) * 8 / 1024 AS mb_used
FROM sys.dm_os_buffer_descriptors osb
INNER JOIN sys.databases d ON d.database_id = osb.database_id;

AIX - CPU, memory and IO (disks space) commands

CPU usage for each process:
topas –P

CPU details:
mpstat

Memory details:
vmstat
svmon

Disk IO details:
iostat
topas -D 

Troubleshoot Microsoft SQL Server memory consumption issues - DBCC MEMORYSTATUS

DBCC MEMORYSTATUS

Return a lot of data about the memory st5atus in the SQL Server.

Get details of all of the queries here:

https://support.microsoft.com/en-us/help/907877/how-to-use-the-dbcc-memorystatus-command-to-monitor-memory-usage-on-sql-server-2005