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  • Cardinality Estimation for Disjunctive Predicates in SQL Server 2014

    Introduction Back in January 2014, I wrote an article for SQLperformance.com describing the cardinality estimation process for queries with multiple predicates, from the point of view of the old and new cardinality estimators. The article describes the various behaviours and formulas involved, along with the usual sprinkling of documented and ...
    Posted to Page Free Space (Weblog) by Paul White on April 15, 2014
  • Geek City: SQL Server 2014 In-Memory OLTP (“Hekaton”) Whitepaper for CTP2

    Last week at the PASS Summit in Charlotte, NC, the update of my whitepaper for CTP2 was released. The manager supervising the paper at Microsoft told me that David DeWitt himself said some very nice things about the technical quality of the paper, which was one of the most ego enhancing compliments I have ever gotten! Unfortunately, Dr. DeWitt ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on October 20, 2013
  • SQL File Layout Viewer 1.2

    Just ahead of presenting it at SQL Saturday in my home town of Minneapolis / Saint Paul, I’m happy to release an updated version of the SQL Server File Layout Viewer. This is a utility I released back in March for inspecting the arrangement of data pages in SQL Server files. If you will be in Minneapolis this Saturday (space permitting), please ...
    Posted to Merrill Aldrich (Weblog) by merrillaldrich on October 9, 2013
  • Wait Statistics in Microsoft SQL Server

     (Originally appearing at http://kevinekline.com/2013/10/09/wait-statistics-in-sql-server/).When it comes to troubleshooting in relational databases, there's no better place to start than wait statistics.  In a nutshell, a wait statistic is an internal counter that tells you how long the database spent waiting for a particular ...
    Posted to Kevin Kline (Weblog) by KKline on October 9, 2013
  • Nested Loops Prefetching

    Nested loops join query plans can be a lot more interesting (and complicated!) than is commonly realized. One query plan area I get asked about a lot is prefetching. It is not documented in full detail anywhere, so this seems like a good topic to address in a blog post. The examples used in this article are based on questions asked by Adam ...
    Posted to Page Free Space (Weblog) by Paul White on August 30, 2013
  • Incorrect Results Caused By Adding an Index

    It’s not often that a SQL Server bug really surprises me or makes me wonder how it was never spotted before, but this is one of those. To get right into it, say you have the following two tables: CREATE PARTITION FUNCTION PF (integer) AS RANGE RIGHT FOR VALUES (1000, 2000, 3000, 4000, 5000);   ...
    Posted to Page Free Space (Weblog) by Paul White on August 20, 2013
  • Geek City: SQL Server 2014 In-Memory OLTP (“Hekaton”) Whitepaper

    Tech Ed isn’t even over yet, and my new Hekaton Whitepaper is already generating questions I can’t answer yet! Here are the two questions that were in my inbox this morning: 1. The whitepaper says “There are other wait types, such as waiting for a log write to complete.” Does this mean that writing to the transaction log  will be ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on June 5, 2013
  • Geek City: Document more trace flags?

      It’s been over 5 years since I last blogged about trace flags, so it seems a post on the topic is in order. If a trace flag is undocumented, it means it is unsupported and not guaranteed. It can go away at any time, even from one service pack to the next. If a trace flag doesn’t work the way the person who told you about said it should ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on June 3, 2013
  • File Layout Viewer vs. Drop Clustered Index

    I had a very educational exchange the other day on Twitter (also known as “getting schooled”) by my SQL compatriots Argenis Fernandez (@DBArgenis) and Hugo Kornelis (@Hugo_Kornelis). A guy called Chris Switalski (@crswit) asked a really interesting question on #sqlhelp, which I proceeded to answer incorrectly, which led to a correction by my ...
    Posted to Merrill Aldrich (Weblog) by merrillaldrich on June 3, 2013
  • Execution Plan Analysis: The Mystery Work Table

    I love SQL Server execution plans. It is often easy to spot the cause of a performance problem just by looking at one. The task is considerably easier if the plan includes run-time information (a so-called ‘actual’ execution plan), but even a compiled plan can be very useful. Nevertheless, there are still times where the execution plan does not ...
    Posted to Page Free Space (Weblog) by Paul White on March 7, 2013
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