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Query store : Query with high variance report RRS feed

  • Question

  • Let's have a look on the above figure:.

    And I am wonder why  std deviation is larger than the variance ???

    suppose:  variance= square of standard deviation

    Monday, September 2, 2019 4:50 AM

All replies

  • anyone also has this wonder?

    Monday, September 2, 2019 3:38 PM
  • Generally high std deviation means parameter sniffing...

    Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/

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    Tuesday, September 3, 2019 4:45 AM
    Moderator
  • Hi sakurai_db,

    Parameterization problems creates a high variation of the query execution. Sometimes the query runs well and very fast, sometimes the query will be very slow. Query Store keeps track of the standard deviation of the query execution and, due to the parameterization problem, the standard deviation will be high.

    Please refer to this blog and Query Store and Parameterization Problems to get more information.

    Best regards,
    Cathy

    MSDN Community Support
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    Tuesday, September 3, 2019 6:44 AM
  • I am not meaning why causing std deviation / variance

    the value of two is not correct!!

    variance should larger than std deviation.....!!!!!

    Tuesday, September 3, 2019 7:06 PM
  • I am not meaning why causing std deviation / variance

    the value of two is not correct!!

    variance should larger than std deviation.....!!!!!

      Hi,

      I checked your question from original post, the question is "And I am wonder why  std deviation is larger than the variance ???"

     Why did you say "variance should larger than std deviation.....!!!!!'', where did you get the information? Could you share it with me. thanks!

    Thursday, September 5, 2019 9:23 AM
  • Seems like a legit question to me. Its been a while since I did maths, to speak of, so just to be certain checking it up in the Internet, we see that "The standard deviation is the square root of the variance"

    This would mean that standard deviation would be lower than variance.

    However, looking that this screenshot more closely, you see that it doesn't say "variance". It says "Variation". That changes things. Whether that report uses "Variation" in any formal way, I can't say. But, again using Internet for help, clearly variance is *not* interchangeable to variation. Here are a couple of a quotes I found, for example:

    "Variation reveals just only the dispersion of the values from their center. Where as variance quantifies the dispersion of the values from their center"

    "Variance has a formula. Variation has no one formula, it is a generic term."

    https://stats.stackexchange.com/questions/88348/is-variation-the-same-as-variance


    Tibor Karaszi, SQL Server MVP (Web Blog)

    Thursday, September 5, 2019 10:13 AM
  • haha.... so what's the calculation behind the ""Variation"" showing up in the Querystore dashboard ?~?!~?
    Friday, September 6, 2019 9:34 AM