Skip to main content

SQL Server Page Life Expectancy (PLE)

SQL Server Page Life Expectancy (PLE) Counter key performance indicator for those DBAs looking at the overall health of their database instance.

Page life expectancy (PLE) -Indicates the number of seconds a page will stay in the buffer pool without references.

The recommended value of the PLE counter is (updated: 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 the 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 the hard drive to read the data.

Some Important point to know about PLE, If you have a server with 64 GB of memory with 56 GB allocated to SQL Server, which means you’re reading about 56 GB of data from disk every 300 seconds. If you look at Page 36 of Troubleshooting SQL Server – A Guide for the Accidental DBA by Jonathan Kehayias and Ted Krueger you’ll see an actual scalable version of this; PLE should be 300 for every 4 GB of RAM on your server. That means for 64 GB of memory you should be looking at closer to 4,800 as what you should view as a critical point.

The reason you see 300 written everywhere is because we were limited by 32-bit servers for so long while at the same time SQL Server documentation was really being developed well.  Those servers could only have 4 GB of memory, thus making this number make sense as well as the Buffer Pool / 4 GB * 300 formula.  I’ll go so far as to say that you should be cautious of anything that doesn’t have a formula to it because our servers keep getting faster, our databases keep getting bigger, and static values…don’t.

Expert comment on PLE -
I'm suggesting is that you don't need to panic every time PLE counter. There isn't always going to be a problem to solve. I wouldn't have anything set up to alert on PLE.

You can find the value of the Page life expectancy (PLE) by running the following query.

Query 1-

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

Query 2-

SELECT [object_name],
[cntr_value] FROM sys.dm_os_performance_counters
WHERE [counter_name] = 'Page life expectancy' --if multiple NUMA on a server should return multiple Nodes,
OR [counter_name] = 'Free list stalls/sec'  -- Number of requests per second that had to wait for a free page
OR [counter_name] = 'Lazy writes/sec' --Flushes of dirty pages before a checkpoint runs. 
OR [counter_name] = 'Buffer cache hit ratio' --percentage of pages found in the buffer cache without having to read from disk you want this ratio to be high
Order by [counter_name] DESC, [object_name];

Query 3-

--plan cache Life expectancy
SELECT sys.dm_exec_cached_plans.objtype AS [CacheType]
,    COUNT_BIG(*) AS [Total Plans]
,    SUM(CAST(sys.dm_exec_cached_plans.size_in_bytes AS DECIMAL(18, 2))) / 1024 / 1024 AS [Total MBs]
,   AVG(sys.dm_exec_cached_plans.usecounts) AS [Avg Use Count]
,   AVG (DATEDIFF(MINUTE, PH_Time.creation_time, (GETDATE()))) AS [Avg Age in Minutes]
FROM sys.dm_exec_cached_plans
left join (
            Select  plan_handle
            , Min (creation_time) as creation_time --A plan can have several unique related quiries, this gets just one time per plan
            from sys.dm_exec_query_stats
            group by plan_handle
            ) as PH_Time On sys.dm_exec_cached_plans.plan_handle = PH_Time.plan_handle
--left join sys.dm_exec_query_stats On sys.dm_exec_cached_plans.plan_handle = sys.dm_exec_query_stats.plan_handle
GROUP BY objtype

How to Fixing Page Life Expectancy (PLE)?
There are lists of ways you can trim down on the space you need.
1.     Drop Unused Indexes
2.     Merge Duplicate Indexes
3.     Use Your Indexes – SARGability
4.     Watch for Big Queries
5.     Look in Your Proc Cache for Opportunities
6.     Know What’s in Your Buffer Pool
7.     Index Maintenance – Defrag
8.     Index Maintenance – Statistics
9.     Purge Your Data
10.  Other
You can also check the more details to fixing Page Life Expectancy (PLE), using the below,

Reface link -

Index Searches
Number of index searches per second. These are used to start range scans and single index record fetches and to reposition an index.

Cause: In general the number of Index is recommended to be high. This means that more searches are being performed thru the use of indexes rather than full scans. This is preferable. However on large databases where the data is constantly changing, if this value starts to decrease and the full scan value starts to increase. It is possible that the statistics for the tables and indexes need to be updated.

Action: Update the statistics for the affected tables. Use Enterprise Manager to reschedule when statistics samples are updated. They may not be occurring frequently enough, or they may not be scheduled at all. In this case set 'auto update statistics' database option on all your databases.
By Anil Singh | Rating of this article (*****)

Popular posts from this blog

List of Countries, Nationalities and their Code In Excel File

Download JSON file for this List - Click on JSON file    Countries List, Nationalities and Code Excel ID Country Country Code Nationality Person 1 UNITED KINGDOM GB British a Briton 2 ARGENTINA AR Argentinian an Argentinian 3 AUSTRALIA AU Australian an Australian 4 BAHAMAS BS Bahamian a Bahamian 5 BELGIUM BE Belgian a Belgian 6 BRAZIL BR Brazilian a Brazilian 7 CANADA CA Canadian a Canadian 8 CHINA CN Chinese a Chinese 9 COLOMBIA CO Colombian a Colombian 10 CUBA CU Cuban a Cuban 11 DOMINICAN REPUBLIC DO Dominican a Dominican 12 ECUADOR EC Ecuadorean an Ecuadorean 13 EL SALVADOR

39 Best Object Oriented JavaScript Interview Questions and Answers

Most Popular 37 Key Questions for JavaScript Interviews. What is Object in JavaScript? What is the Prototype object in JavaScript and how it is used? What is "this"? What is its value? Explain why "self" is needed instead of "this". What is a Closure and why are they so useful to us? Explain how to write class methods vs. instance methods. Can you explain the difference between == and ===? Can you explain the difference between call and apply? Explain why Asynchronous code is important in JavaScript? Can you please tell me a story about JavaScript performance problems? Tell me your JavaScript Naming Convention? How do you define a class and its constructor? What is Hoisted in JavaScript? What is function overloadin

React | Encryption and Decryption Data/Text using CryptoJs

To encrypt and decrypt data, simply use encrypt () and decrypt () function from an instance of crypto-js. Node.js (Install) Requirements: 1.       Node.js 2.       npm (Node.js package manager) 3.       npm install crypto-js npm   install   crypto - js Usage - Step 1 - Import var   CryptoJS  =  require ( "crypto-js" ); Step 2 - Encrypt    // Encrypt    var   ciphertext  =  CryptoJS . AES . encrypt ( JSON . stringify ( data ),  'my-secret-key@123' ). toString (); Step 3 -Decrypt    // Decrypt    var   bytes  =  CryptoJS . AES . decrypt ( ciphertext ,  'my-secret-key@123' );    var   decryptedData  =  JSON . parse ( bytes . toString ( CryptoJS . enc . Utf8 )); As an Example,   import   React   from   'react' ; import   './App.css' ; //Including all libraries, for access to extra methods. var   CryptoJS  =  require ( "crypto-js" ); function   App () {    var   data

25 Best Vue.js 2 Interview Questions and Answers

What Is Vue.js? The Vue.js is a progressive JavaScript framework and used to building the interactive user interfaces and also it’s focused on the view layer only (front end). The Vue.js is easy to integrate with other libraries and others existing projects. Vue.js is very popular for Single Page Applications developments. The Vue.js is lighter, smaller in size and so faster. It also supports the MVVM ( Model-View-ViewModel ) pattern. The Vue.js is supporting to multiple Components and libraries like - ü   Tables and data grids ü   Notifications ü   Loader ü   Calendar ü   Display time, date and age ü   Progress Bar ü   Tooltip ü   Overlay ü   Icons ü   Menu ü   Charts ü   Map ü   Pdf viewer ü   And so on The Vue.js was developed by “ Evan You ”, an Ex Google software engineer. The latest version is Vue.js 2. The Vue.js 2 is very similar to Angular because Evan You was inspired by Angular and the Vue.js 2 components looks like -

Encryption and Decryption Data/Password in Angular

You can use crypto.js to encrypt data. We have used 'crypto-js'.   Follow the below steps, Steps 1 –  Install CryptoJS using below NPM commands in your project directory npm install crypto-js --save npm install @types/crypto-js –save After installing both above commands it looks like  – NPM Command  1 ->   npm install crypto-js --save NPM Command  2 ->   npm install @types/crypto-js --save Steps 2  - Add the script path in “ angular.json ” file. "scripts" : [                "../node_modules/crypto-js/crypto-js.js"               ] Steps 3 –  Create a service class “ EncrDecrService ” for  encrypts and decrypts get/set methods . Import “ CryptoJS ” in the service for using  encrypt and decrypt get/set methods . import  {  Injectable  }  from   '@angular/core' ; import   *   as   CryptoJS   from   'crypto-js' ; @ Injectable ({    providedIn:   'root' }) export   class   EncrDecrS