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  • SQL Server Internals: 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 Paul White: Page Free Space (Weblog) by Paul White on August 30, 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 Paul White: Page Free Space (Weblog) by Paul White on March 7, 2013
  • Optimizing T-SQL queries that change data

    Most tuning efforts for data-changing operations concentrate on the SELECT side of the query plan. Sometimes people will also look at important storage engine considerations like locking and transaction log throughput that can have dramatic effects. As a consequence, a number of common practices have emerged, such as avoiding large numbers of ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on January 25, 2013
  • Temporary Table Caching Explained

    SQL Server 2005 onward caches temporary tables and table variables referenced in stored procedures for reuse, reducing contention on tempdb allocation structures and catalogue tables.  A number of things can prevent this caching (none of which are allowed when working with table variables): Named constraints (bad idea anyway, since ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on August 16, 2012
  • Query Optimizer Deep Dive - Part 4

    This is the final part in a series of posts based on the content of the Query Optimizer Deep Dive presentations I have given over the last month or so at the Auckland SQL Users’ Group and the SQL Saturday events in Wellington, New Zealand and Adelaide, Australia. Links to other parts of this series: Part 1 Part 2 Part 3 Beating the Optimizer ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on April 30, 2012
  • Query Optimizer Deep Dive – Part 3

    This is the third part in a series of posts based on the content of the Query Optimizer Deep Dive presentations I have given over the last month or so at the Auckland SQL Users’ Group and the SQL Saturday events in Wellington, New Zealand and Adelaide, Australia. Links to other parts of this series: Part 1 Part 2 Part 4 Storage of Alternative ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on April 29, 2012
  • Query Optimizer Deep Dive – Part 2

    This is the second part in a series of posts based on the content of the Query Optimizer Deep Dive presentations I have given over the last month or so at the Auckland SQL Users’ Group and the SQL Saturday events in Wellington, New Zealand and Adelaide, Australia. Links to other parts of this series: Part 1 Part 3 Part 4 Cost-Based Optimization ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on April 28, 2012
  • Query Optimizer Deep Dive - Part 1

    This is the first in a series of posts based on the content of the Query Optimizer Deep Dive presentations I have given over the last month or so at the Auckland SQL Users’ Group and the SQL Saturday events in Wellington, New Zealand and Adelaide, Australia. Links to other parts of this series: Part 2 Part 3 Part 4 Introduction The motivation ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on April 27, 2012
  • Forcing a Parallel Query Execution Plan

    This post is for SQL Server developers who have experienced the special kind of frustration, which only comes from spending hours trying to convince the query optimizer to generate a parallel execution plan.  This situation often occurs when making an apparently innocuous change to the text of a moderately complex query; a change which ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on December 22, 2011
  • SQL Server, Seeks, and Binary Search

    The following table summarizes the results from my last two blog entries, showing the CPU time used when performing 5 million clustered index seeks: In test 1, making the clustered index unique improved performance by around 40%. In test 2, making the same change reduced performance by around 70% (on 64-bit systems – more on that later).  ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on August 8, 2011
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