Blog - Title

  • Conor vs. SQL

    Conor vs. Misbehaving Parameterized Queries + OPTIMIZE FOR hints

    • 15 Comments
    In my previous post, I debugged a customer problem for you, including the various guesses I had to make and why they matter. The specific problem was likely related to parameter sensitivity, an issue in query optimization where the optimizer will try...
  • Conor vs. SQL

    Conor vs. more SARGable predicates

    • 7 Comments
    I got another question in the mail this week from another reader:   Hi Conor Thanks for an interesting blog. Maybe you have the answer to this question: Why I SQL Server having performance problems with these types of expressions: --------------...
  • Conor vs. SQL

    Conor vs. Sinergija 2011

    • 7 Comments
    As a professional announcement, I will not be speaking at PASS this year (nor will I be at the conference).  Instead, I will be in Belgrade, Serbia the following week to speak at the Sinergija 11 conference.  I’ll be doing a talk on the new...
  • Conor vs. SQL

    Conor vs. SQLBits X Slide Decks

    • 6 Comments
    Thanks for all who attended SQLBits last weekend and for those of you who attended my talks. I had three talks this time at SQLBits, including the technical keynote on Saturday.  I’ve attached these decks for your reference here: Making DW Easy ppt...
  • Conor vs. SQL

    Conor vs. Left Outer Join Reordering

    • 5 Comments
    A question from two of the MVPs: Are these two queries conceptually the same? select a.id, b.id, c.id from A left join C on A.id = C.id left join B on A.id = B.id;   select a.id, b.id, c.id from A left join B on A.id = B.id left join C on A.id =...
  • Conor vs. SQL

    Conor vs. Anti-Semi-Join Reordering

    • 4 Comments
    I was asked to comment on a post about the order of WHERE NOT EXISTS (<subquery>) in a query and its impact on a query plan. Specifically this thread: http://social.msdn.microsoft.com/Forums/en/transactsql/thread/278c272b-5ebb-4fda-8985-49927bbd3799...
  • Conor vs. SQL

    Conor vs. Updates – Talk (for those of you in Austin)

    • 4 Comments
    I am giving a talk tomorrow (Tuesday) night at the Austin PASS group on how Update Queries are processed/optimized in SQL Server.  The talk will be at the Microsoft office in Austin (which recently moved). More details can be found at the CACTUS...
  • Conor vs. SQL

    Conor vs. Finding a Misbehaving Query

    • 4 Comments
    (well, one case of it – the topic is too large for a blog post, so I will focus) I will paraphrase a question I received over the weekend from a SQL Server user: “My server is doing fine.  all of a sudden CPU use goes to 100% and stays there. ...
  • Conor vs. SQL

    Conor vs. PASS (Slide Decks)

    • 4 Comments
    I had a great time at PASS last week and got to talk to a lot of wonderful customers- thank you! As promised, here are the decks: Update Talk Performance Troubleshooting Talk Happy Querying! Conor
  • Conor vs. SQL

    No Seatbelt - Expecting Order without ORDER BY

    • 4 Comments
    One of the greatest lessons I've learned in building software is that every technical implementation has a human element to how it is used, perceived, and interpreted. While I've seen my share of poor technical solutions to problems, sometimes the most...
  • Conor vs. SQL

    Conor vs. Isolation Level Upgrade on UPDATE/DELETE Cascading RI

    • 4 Comments
    A customer recently asked our support organization about an unexplained series of range locks that they were seeing on a DELETE to a table with a foreign key. Here is the repro:   1: create table Foo (FooId int not null primary key ) 2: create...
  • Conor vs. SQL

    Conor vs. “Does Join Order Matter?”

    • 4 Comments
    I got this question/claim again this week, so I’ll write a blog post on it while I wait for my build to complete: It usually goes something like “When I rewrite my query, SQL Server gives me a different plan.  Therefore, I should rewrite all my queries...
  • Conor vs. SQL

    SQL Server 2008 Internals Book Now Available!

    • 3 Comments
    For those of you waiting for the new "Inside SQL Server" book, it is actually out now.  Kalen decided to give it a name change, and the actual title is "SQL Server 2008 Internals".  I've written a chapter on how the Query...
  • Conor vs. SQL

    OPTIMIZE FOR UNKNOWN - How could that possibly make any sense???

    • 3 Comments
    Yes, I'm alive. I have been chatting with my wife about the times I need to "go dark" - in this case, I am working on features that I can't discuss yet, other than to say that I am *very* excited to go to work every day.. (well, since I work out of...
  • Conor vs. SQL

    Foreign Keys are our friends...

    • 3 Comments
    I often find customers who question the value of database-enforced integrity constraints. While people often create primary keys, the foreign ones are perhaps a bit more .... well, foreign. Let's start at the beginning. In traditional, old-school database...
  • Conor vs. SQL

    Darn Gigabit switches...

    • 3 Comments
    I had a netgear gs108 (8 port gigabit switch) die on me this evening. Perhaps it is me working from home.. Perhaps it is the high temperatures in Austin this time of year.. Perhaps it is the humidity from Hurricane Dolly. Who knows... I have patched...
  • Conor vs. SQL

    Statistics Sample Rates

    • 3 Comments
    I had a question about sample rates for statistics yesterday for SQL Server 200x statistics. Here is my basic rule-of-thumb. 1. If you have no issues with statistics or query plan quality, then you can leave it alone and not think about it. 2. If...
  • Conor vs. SQL

    Conor vs. PASS

    • 3 Comments
    It’s one of the most exciting weeks of the year to be a SQL Server junkie – PASS is this week in Seattle! I’m giving a talk on the many details of Update queries.  It will cover the various operators and how they work, why the plan shapes look the...
  • Conor vs. SQL

    Conor vs. Join Algorithms

    • 3 Comments
    I got a question from a customer today related to join algorithms.  This is a good, general topic, so I will post a few notes on this in the hopes that it is interesting to anyone out there who doesn’t understand how the costing formulas are put...
  • Conor vs. SQL

    Conor vs. UDFs in Joins

    • 3 Comments
    In my previous post, I reviewed the basic logic behind why the Optimizer chooses one join algorithm over another.  In this post, I’ll go one step further and discuss what happens when the basic logic for joins is combined with the logic for how UDFs...
  • Conor vs. SQL

    Conor vs. SQLBits

    • 3 Comments
    A quick announcement to let you know that I will be speaking at the SQLBits conference in London on April 16th.  My talk will be a 400-level talk on how the Query Optimizer works.  I am excited to get to go to London to talk to people about...
  • Conor vs. SQL

    Conor vs. Runtime Constant Functions

    • 3 Comments
    (more questions resulting from SQL Bits – some of these answers will be a bit more terse than my usual verbose self :))   A customer asked a different question and I need to introduce a concept to you before I can answer that question, so I will...
  • Conor vs. SQL

    Conor vs. Optional Parameters

    • 2 Comments
    One question I received at SQL Bits had to do with a reasonable programming practice that has an unintended performance impact.   SELECT <something> FROM T WHERE (@p is NULL or col = @p)   This pattern is common and we call it the “optional...
  • Conor vs. SQL

    Conor vs. SQL Azure/SQL Server 2012

    • 2 Comments
    I’m not one for New Year’s Resolutions, but I am going to try to blog a bit more.  It’s hard to describe working at Microsoft, especially as one gets more senior.  There are lots of really smart people.  There’s an ability to work on problems...
  • Conor vs. SQL

    Conor vs. Distributed Query Provider Hints

    • 2 Comments
    (I promised I’d write more ) Today I will talk a bit about Distributed Query (DQ), a feature that lets you query across databases/servers.  I’ve previously posted an academic paper we wrote on the subject some time back ( http://citeseerx.ist.psu...
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