Page life expectancy

General Rule:

PLE Formula : (max memory in GB) / 4 * 300

Max Memory in GB represents sql Allocation Memory

If SQL Allocated Memory is 32 GB.

Then select (32/4)*300=2400 or 40  minutes

If PLE value less than 40 then indicate Memory issue.

SELECT  @@servername AS INSTANCE

,[object_name]

,[counter_name]

, UPTIME_MIN = CASE WHEN[counter_name]= 'Page life expectancy'

          THEN (SELECT DATEDIFF(MI, MAX(login_time),GETDATE())

          FROM   master.sys.sysprocesses

          WHERE  cmd='LAZY WRITER')

      ELSE ''

END

, [cntr_value] AS PLE_SECS

,[cntr_value]/ 60 AS PLE_MINS

,[cntr_value]/ 3600 AS PLE_HOURS

,[cntr_value]/ 86400 AS PLE_DAYS

FROM  sys.dm_os_performance_counters

WHERE   [object_name] LIKE '%Manager%'

          AND[counter_name] = 'Page life expectancy'


In practical , PLE should be in three digits.