What is PLE? ( page life expectancy )

Page Life Expectancy (PLE) metric has long been considered a key performance indicator for DBAs looking at the overall health of their database instances. PLE shows whether the system is under internal memory pressure using counters provided by the Buffer Manager Object.

PLE is a measure of the length of time (in seconds) a data file page is expected to stay in SQL Server’s buffer pool. This metric is not an aggregate or accumulation, but simply a point-in-time value that DBAs will query out of the Buffer Manager.

SQL Server only reads data pages from the buffer pool (i.e., logical read), so if the page isn’t in the buffer pool, it finds it on the disk (i.e., physical read) and moves the page to the buffer pool so it can do a logical read. This is a time-consuming process and can negatively affect performance.

A high PLE value means a page is staying in the buffer pool longer, so SQL Server is less likely to have to go to disk looking for the data page, which makes the system run faster.

Historically, DBAs considered 300 seconds (five minutes) the PLE sweet spot. However, that number is fairly arbitrary. Microsoft recommended 300 as the PLE standard back in the 2000s when memory was limited.

Today, DBAs don’t focus on a “right” number because buckets of memory come standard on most systems. It’s not unusual for SQL Server to run on a system that has TBs of RAM at its disposal, so DBAs have adopted a formulaic approach to identifying a “good” PLE value:

Page Life Expectancy = 300 seconds for every 4 GB of RAM on your server.

You can check below with the script

SELECT [object_name],

[counter_name],

[cntr_value]

FROM sys.dm_os_performance_counters

WHERE

[object_name] LIKE ‘%Manager%’ AND

[counter_name] = ‘Page life expectancy’