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Difference between Page Reads/Sec in "Memory" and "Buffer Manager" in perfmon

    Question

  • Hi

    I'm capturing some performance stats of a sql server instance and Performance Objects "Memory" and "Buffer Manager"both have a counter for "Page Reads/Sec". I've read the definitions a few times and it's not sinking in what the difference is for the counter between the 2 performance objects and i can see the values returned by perfmon are somewhat different.

    Could anyone explain what the difference is?

    Cheers

    • Moved by Tom PhillipsModerator Thursday, January 16, 2014 3:18 PM Probably better database engine question
    Thursday, January 16, 2014 3:08 PM

Answers

  • So far the answers have been basically regurgitated from the perfmon descriptions.  Allow me to try to put it into simpler English:

    Memory: Page Reads/Sec - this counter tracks the number of pages that the OS (Windows Server) reads from the disk to satisfy requests for data on disk which isn't already in the Windows cache.

    SQL Server:Buffer Manager: Page Reads/Sec - this counter tracks the number of pages that SQL Server reads from the disk to satisfy query requests.

    When a "SQL Server:Buffer Manager: Page Reads/Sec" event occurs SQL Server requests data from the OS.  The OS then looks into it's cache to see if the required data is there.  If the OS determines that the data requested by SQL Server isn't in the OS's cache then the OS reads the data from disk and delivers it to SQL Server which results in a "Memory: Page Reads/Sec" event.  If the OS determines that the data requested by SQL Server is in the OS's cache then the OS returns the requested data to SQL Server from the OS's cache and no "Memory: Page Reads/Sec" event occurs.

    Thursday, January 16, 2014 6:43 PM

All replies

  • Hello,

    Hope you are aware about fact that SQL server major memory consumer is buffer pool but not all .There are memory allocated to SQL server directly through windows which does not come under buffer pool.These are memory for requests greater that 8 KB( large pages).

    Now Counter SQL server :Buffer manager gives you memory  consumption for buffer manager

    While memory counter deals with total memory SQL server is using.

    As far as pages read/sec is it signifies how much page was brought into memory for reading or may be writing

    I have not tried to find out difference but I hope this is what it means.You can check that

    Hope this helps


    Please mark this reply as the answer or vote as helpful, as appropriate, to make it useful for other readers


    • Edited by Shanky_621 Thursday, January 16, 2014 3:35 PM
    Thursday, January 16, 2014 3:33 PM
  • Hi,

     Memory :Pages Reads/Sec - OS level  (Read and Write)- Pages/sec is the rate at which pages are read from or Written to Disk to resolve Pageout issue(HardFaults).


    Buffer: Pages Reads/Sec - Database - Number of physical database page reads per second(Only Read).


    -Prashanth

    Thursday, January 16, 2014 3:49 PM
  • So far the answers have been basically regurgitated from the perfmon descriptions.  Allow me to try to put it into simpler English:

    Memory: Page Reads/Sec - this counter tracks the number of pages that the OS (Windows Server) reads from the disk to satisfy requests for data on disk which isn't already in the Windows cache.

    SQL Server:Buffer Manager: Page Reads/Sec - this counter tracks the number of pages that SQL Server reads from the disk to satisfy query requests.

    When a "SQL Server:Buffer Manager: Page Reads/Sec" event occurs SQL Server requests data from the OS.  The OS then looks into it's cache to see if the required data is there.  If the OS determines that the data requested by SQL Server isn't in the OS's cache then the OS reads the data from disk and delivers it to SQL Server which results in a "Memory: Page Reads/Sec" event.  If the OS determines that the data requested by SQL Server is in the OS's cache then the OS returns the requested data to SQL Server from the OS's cache and no "Memory: Page Reads/Sec" event occurs.

    Thursday, January 16, 2014 6:43 PM
  • Hi

    I'm capturing some performance stats of a sql server instance and Performance Objects "Memory" and "Buffer Manager"both have a counter for "Page Reads/Sec". I've read the definitions a few times and it's not sinking in what the difference is for the counter between the 2 performance objects and i can see the values returned by perfmon are somewhat different.

    Could anyone explain what the difference is?

    Cheers

    you will get good information from Jon-

    Great SQL Server Debates: Buffer Cache Hit Ratio

    https://www.simple-talk.com/content/article.aspx?article=1426


    Thanks, Rama Udaya.K (http://rama38udaya.wordpress.com) ---------------------------------------- Please remember to mark the replies as answers if they help and UN-mark them if they provide no help,Vote if they gives you information.

    Thursday, January 16, 2014 8:02 PM