During performance tuning consultation there are plenty of counters and values, I often come across. Today we will quickly talk about Page Life Expectancy counter, which is commonly known as PLE as well.
You can find the value of the PLE by running following query.
WHERE [object_name] LIKE '%Manager%'
AND [counter_name] = 'Page life expectancy'
The recommended value of the PLE counter is (update: minimum of) 300 seconds. I have seen on busy system this value to be as low as even 45 seconds and on unused system as high as 1250 seconds. Page Life Expectancy is number of seconds a page will stay in the buffer pool without references. In simple words, if your page stays longer in the buffer pool (area of the memory cache) your PLE is higher, leading to higher performance as every time request comes there are chances it may find its data in the cache itself instead of going to hard drive to read the data.
Now check your system and post back what is this counter value for you during various time of the day. Is this counter any way relates to performance issues for your system?
Note: There are various other counters which are important to discuss during the performance tuning and this counter is not everything.
Update: PLE counter should be me 300 or more (OLTP Blueprint – A Performance Profile of OLTP applications)
Reference: Pinal Dave (http://blog.SQLAuthority.com)