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  • A Tale of Two Index Hints

    If you look up Table Hints in Books Online, you’ll find the following statement: If a clustered index exists, INDEX(0) forces a clustered index scan and INDEX(1) forces a clustered index scan or seek. If no clustered index exists, INDEX(0) forces a table scan and INDEX(1) is interpreted as an error. The interesting thing there is ...
    Posted to Page Free Space (Weblog) by Paul White on September 22, 2010
  • Did You Know? Lost Without a Trace

    This is not a post about Jim Gray, much as I wish I had some news to share. It's about one of the reasons you should be really careful about using undocumented trace flags. I always try to warn people, whether I'm writing or speaking, about the dangers inherent when using any undocumented feature. Undocumented means unsupported! Microsoft retains ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on February 26, 2008
  • Join and Query hints – serious DBAs need to learn this

    For a long time, I have refrained from endorsing the use of Join and Query Hints. The reason is that there is no such thing as query hints in SQL Server except for a few simple items. The key options listed under Microsoft SQL Server Hints (Transact-SQL) that affect join order, join type, and index usage are not really hints. They are in ...
    Posted to Joe Chang (Weblog) by jchang on December 1, 2015
  • Inside the Optimizer: Constructing a Plan – Part 4

    Summary: More undocumented ways to explore how the query optimiser works. This post is part of a series: Part1 Part 2 Part3 Part4 Documented Rule-Affecting Options It might surprise you to learn that most T-SQL users have written queries that disable one or more of the optimiser rules already. Join hints { LOOP | HASH | MERGE | ...
    Posted to Page Free Space (Weblog) by Paul White on July 31, 2010
  • Bushy Joins

    A great session by Adam Machanic at SQL Saturday Boston the previous weekend on methods to influence the query optimizer while still letting it do its task. The gist of this is that while SQL Server has what are called Query Hints, there are adverse consequences. The Join Hints (Loop, Hash and Merge) "specify that the query optimizer ...
    Posted to Joe Chang (Weblog) by jchang on April 2, 2014
  • Honed my Mad Transaction Isolation Skillz

    At the Summit today I attended what was basically a Transaction Isolation Level boot-camp, with the ever-illuminating Kalen Delaney. If Isolation Levels were biceps, Locking Hints were pecs and transaction-related DMVs were six-pack abs, I have to say that Ms. Delaney whipped us all into amazing shape. In this, at least, I am now what the ...
    Posted to Merrill Aldrich (Weblog) by merrillaldrich on November 9, 2010
  • Geek City: 24Hours of PASS Followup

    Thank you everyone who attended my 24HOP session yesterday. It was a wonderful event to be part of. Here are a few of the questions that I was asked, that didn't get completely answered. Question: Can we set READ_COMMITTED_SNAPSHOT ON for just a table rather than at database level? I apologize that I answered this incorrectly.  I was ...
    Posted to Kalen Delaney (Weblog) by Kalen Delaney on September 16, 2010
  • Table Scan - Aggregate Cost Structure

    In the previous post, I mention that in an earlier post on IO cost structure, that the cost of a table scan was approximately 1 CPU-micro sec per page, plus approximately 0.05 us per row for just a SELECT COUNT(*) This was calibrated on a 2-way Xeon 5430 Quad-Core 2.66GHz. I should also add that the test tables have a clustered primary key, with ...
    Posted to Joe Chang (Weblog) by jchang on February 27, 2009
  • The first pillar – A Coherent Design

    One of the definitions on wiktionary.org for coherence is “a logical arrangements of parts”. In my initial post, I defined “coherent” for database designs in the following manner: cohesive, comprehendible, standards based, names/datatypes all make sense, needs little documentation.  Both definitions share one specific common theme: ...
    Posted to Louis Davidson (Weblog) by drsql on January 8, 2009
  • Using application locks to implement a critical section in T-SQL code

    This is being added to the addendum (located here) for my ''Pro SQL Server 2005 Database Design and Optimization'' book and would have appeared in the pessimistic locking section on page 478 in Chapter 9: Coding for Integrity and Concurrency; Pessimistic Locking. You can download the entire addendum here: Addendum. The problem of the critical ...
    Posted to Louis Davidson (Weblog) by drsql on May 7, 2007
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