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SQL Server, SQL Server Internals

SQL SERVER – Page Life Expectancy (PLE)

What is Page Life Expectancy (PLE)

On of the key performance measures for SQL Server that you will hear constantly is Page Life Expectancy or PLE for short. So What is PLE you ask? Hopefully this short post will shed some light on that for you.  If you are really inquisitive you can get the current PLE value by running the query below.

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

The current commonly accepted (recommended)  value of the PLE counter is  minimum of  300 seconds. I have seen on this value drop on busy on busy systems to as low as 35 seconds and as high as 1250 seconds on systems that are lightly used. So what do these values actually represent. Page Life Expectancy is number of seconds a page will stay in the buffer pool without references. Huh? In other words, if the page that has you data stays longer in the buffer pool (cached in memory) then your PLE is higher, leading to better performance as every time request comes there are chances it may find its data in the cache (memory) rather then having to go to disk for it. Which as we all know is very costly from a performance perspective.

Again this is just a general performance measure but it is good to establish a base line and check during periods of heavy use, it may also be an indication of memory pressure if you see this KPI drop.

 

Boa Apetite

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About ldgaller

Accomplished Data Warehouse Architect, DBA and Software Architect with over 15 years of professional experience and demonstrated success designing and implementing solutions that improve business functionality and productivity. Highly diverse technical background with proven ability to design, develop and implement technology on an enterprise level. I approach all projects with passion, diligence, integrity, and exceptional aptitude.

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