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Correlation of DTU and RAM in GB allocated to DB RRS feed

  • Question

  • Hi,

     Azure portal  and DMV providing % of memory used

     I want to query  MAX  RAM in GB allocated to server assuming  we have only one customer  database per server 

     DTU 500 = ? GB Ram , DTU 1750 = ? GB Ram

      

    Thank you

    Alex


    • Edited by AlexMtl Tuesday, January 7, 2020 2:51 PM
    Tuesday, January 7, 2020 2:50 PM

All replies

  • Hi,

     Azure portal  and DMV providing % of memory used

     I want to query  MAX  RAM in GB allocated to server assuming  we have only one customer  database per server 

     DTU 500 = ? GB Ram , DTU 1750 = ? GB Ram

    Thank you

    Alex

    Good day Alext,

    DTU and eDTU are a combination of resources and you don't have any guarantee for maximum CPU or maximum RAM. If you need to control the amount of maximum resources which you have then you should use "vCore-based purchasing options" pricing model


    signature   Ronen Ariely
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    Wednesday, January 8, 2020 9:01 AM
    Moderator
  • Hi Alex

    As Ronen already mentioned we cannot directly correlate how many DTU's will amount to how much RAM. As given below in this document the DTU is bundle of compute, IO and Storage.

    If you want more control you will need to move to vCore model. Here is the document for migrating the same.

    https://docs.microsoft.com/en-us/azure/sql-database/sql-database-dtu-to-vcore

    Hope this helps

    Thanks
    Navtej S

    Wednesday, January 8, 2020 2:54 PM
    Moderator
  • Yes MS  clearly explain  that "DTU is bundle of compute, IO and Storage"

    we can use  sys.dm_db_resource_stats

    where we have column avg_memory_usage_percent decimal (5,2) 
    Average memory utilization in percentage of the limit of the service tier.This includes memory used for buffer pool pages and storage of In-Memory OLTP objects.

    if avg_memory_usage_percent = 70%  I want to find   memory limit of the service tier (100%)  is in MB or GB



    Wednesday, January 8, 2020 10:28 PM
  • Hi 

    We are checking this further and will get back to you.

    Thanks
    Navtej S

    Friday, January 10, 2020 6:53 PM
    Moderator
  • Yes MS  clearly explain  that "DTU is bundle of compute, IO and Storage"

    we can use  sys.dm_db_resource_stats

    where we have column avg_memory_usage_percent decimal (5,2) 
    Average memory utilization in percentage of the limit of the service tier.This includes memory used for buffer pool pages and storage of In-Memory OLTP objects.

    if avg_memory_usage_percent = 70%  I want to find   memory limit of the service tier (100%)  is in MB or GB

    Hi,

    >> if avg_memory_usage_percent = 70%  I want to find   memory limit of the service tier (100%)  is in MB or GB

    This is exactly the point. When you use vCore then you have control on the amount of memory and CPU but when you use DTU you do not have the amount of the total numbers and these numbers can changed a bit.

    You know that you used 70% but you do not know 70% of what ;-)
    Since the "from what" is not provided and can be different from time to time. In general you can estimate your use using these values since the resources will not be changed dramatically when you use the specific tier but you cannot count on these numbers as absolute number


    signature   Ronen Ariely
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    Saturday, January 11, 2020 8:54 PM
    Moderator
  • Hi 

    To add to Ronen's answer,here is what we received from PG team as well

    "In the DTU model, the absolute values for memory and number of cores are not documented or guaranteed, and can change over time as long as the DTU benchmark provides similar results for a given service level.

    You can query the sys.dm_os_job_object DMV and examine the value of the process_memory_limit_gb column to determine the amount of memory currently allocated to the SQL Server process."

    Hope this helps.

    Thanks
    Navtej S

    Monday, January 13, 2020 1:08 PM
    Moderator