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Showing page 1 of 49 (485 total posts)
  • Explaining Activity Monitor

    This post is not about how to use the Activity Monitor (AM) tool in SQL Server Management Studio (SSMS) – there are loads of such posts written already. Also, it is not about dissing AM, you will find such posts as well. What I want to do is to explain the information in AM, for instance what time span the information covers. I see lots of ...
    Posted to Tibor Karaszi (Weblog) by TiborKaraszi on February 16, 2017
  • This month’s T-SQL Tuesday post

    …is not here. It’s over at https://sqlperformance.com/2017/01/sql-performance/estimated-number-of-rows-to-be-read I write about the new EstimatedRowsRead property, and in particular, about how Microsoft responded so well to the Connect Item I created, requesting the feature. @rob_farley
    Posted to Rob Farley (Weblog) by rob_farley on January 9, 2017
  • SQL Nexus 5.5.0.1

      The SQL Nexus set of utilities are some of the most under utilized tools available to the SQL Server community. I used and touted the RML utility for many years to help people analyze trace information very fast and easily. Eventually XE traces were added to the list along with much more.  This blog post link will give you a pretty ...
    Posted to Andrew Kelly (Weblog) by Andrew Kelly on November 20, 2016
  • Misconceptions on parameter sniffing

    In my previous post, I explained the basic of parameter sniffing, and then built on that to explain the lesser known mechanics of variable sniffing and cardinality sniffing. However, I also sneakily inserted a few comments on misconceptions about the performance impact of parameter sniffing, with the promise to explain in more detail later. Well … ...
  • The sniffing database

    Your SQL Server instances, like people with hay fever that forget to take their antihistamines during summer, is sniffing all the time. Sniffing is a trick employed by the optimizer in an attempt to give you better execution plans.   The most common form of sniffing is parameter sniffing. Many people know about parameter sniffing, but there ...
  • Query Store - Forced Doesn’t Always Mean Forced

      The new Query Store feature in SQL Server 2016 is a great new addition that we have been anticipating for many years now. There are already a bunch of articles out there that explain what it is even how to go about using it so I won’t repeat that here. However there is one aspect of the feature that has been poorly documented and even a ...
    Posted to Andrew Kelly (Weblog) by Andrew Kelly on September 18, 2016
  • SQLSentry does it Again – Plan Explorer is Completely Free

     Many of us have used the free version of Plan Explorer from SQLSentry for a long time to help tune and explore query plans in a way that SSMS can only dream of. Unlike most free tools this one still had plenty of useful features that served the community well. The Pro version did however contain a bunch of great features that many ...
    Posted to Andrew Kelly (Weblog) by Andrew Kelly on September 8, 2016
  • Log Page Life Expectancy over time

    You often see Page Life Expectancy referred to as an interesting performance monitor counter. And it can be! It indicates for how long a page is expected to stay in cache, from the time it was brought into cache. But just looking at a snapshot value doesn't say that much. It might be high, but that is because you haven't had a high turnover ...
    Posted to Tibor Karaszi (Weblog) by TiborKaraszi on September 7, 2016
  • The DIY guide for local-global aggregation

    If you have read the title, you will not be surprised when I tell you that this blog is about a thing called “local-global aggregation”, and on how to do that yourself. So let’s start with the two obvious questions: what the heck is local-global aggregation anyway, and why the heck would you ever want to do it yourself?   What is ...
  • How TOP wrecks performance (part 2)

    In my previous post, I showed how the vanilla version of TOP can really help performance by nudging the optimizer into picking an execution plan that is optimized for returning just a few rows instead of the entire result set. But I also showed that adding WITH TIES causes a cardinality misestimate, which may lead to suboptimal or downright ...
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