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  • Halloween Protection – The Complete Series

    I have just published a four-part series for SQLPerformance.com on the Halloween Problem. Some of you will never have heard of this issue, and those that have might associate it only with T-SQL UPDATE queries. In fact, the Halloween problem affects execution plans for INSERT, UPDATE, DELETE and MERGE statements. This is a topic I have been ...
    Posted to Page Free Space (Weblog) by Paul White on February 20, 2013
  • One more reason to to understand query plans, not directly performance related

    One of the things that separates a good programmer from a great one is a firm understanding about what is going on inside the computer. For some programming languages, it is very obvious what is going on inside the computer because you are working at a very low level. For example, if you are a C/C++ programmer writing an OS, you will know a lot ...
    Posted to Louis Davidson (Weblog) by drsql on January 22, 2013
  • Learn More About SQL Server IO and Query Tuning in These Webcasts

    I'm doing two new webcasts next week on Wednesday, December 19th, one in the morning and the other after lunch.   SSDs are a Game Changer for SQL Server Storage No, session is not exclusively about SSDs.  But this is my first session on IO and storage tuning that emphasizes SSDs over hard disks.  As Bob Dylan said ''Times, they ...
    Posted to Kevin Kline (Weblog) by KKline on December 14, 2012
  • Beware of SQL Server and PerfMon differences in disk latency calculation

    Recently sp_blitz procedure on one of my OLTP servers returned alarming notification about high latency on one of the disks (more than 100ms per IO). Our chief storage guy didn’t understand what I was talking about – according to his measures, average latency is only about 15ms. In order to investigate the issue, I’ve recorded 2 snapshots of ...
    Posted to Michael Zilberstein (Weblog) by mz1313 on November 27, 2012
  • Quick Tip - Speed a Slow Restore from the Transaction Log

    Here's a quick tip for you:During some restore operations on Microsoft SQL Server, the transaction log redo step might be taking an unusually long time.  Depending somewhat on the version and edition of SQL Server you've installed, you may be able to increase performance by tinkering with the readahead performance for the redo operations. ...
    Posted to Kevin Kline (Weblog) by KKline on November 14, 2012
  • The Zombie PerfMon Counter That Never Dies! Quick Tip

    The PerfMon Counters That Just Won't DieOne of the things that's simultaneously great and horrible about the Internet is that once something gets posted out in the ether, it basically never goes away.  (Some day, politicians will realize this.  We can easily fact check their consistency).  Because of longevity of content posted to ...
    Posted to Kevin Kline (Weblog) by KKline on October 8, 2012
  • Why Doesn’t Partition Elimination Work?

    Given a partitioned table and a simple SELECT query that compares the partitioning column to a single literal value, why does SQL Server read all the partitions when it seems obvious that only one partition needs to be examined? Sample Data The following script creates a table, partitioned on the char(3) column ‘Div’, and populates it with ...
    Posted to Page Free Space (Weblog) by Paul White on September 11, 2012
  • Compute Scalars, Expressions and Execution Plan Performance

    The humble Compute Scalar is one of the least well-understood of the execution plan operators, and usually the last place people look for query performance problems.  It often appears in execution plans with a very low (or even zero) cost, which goes some way to explaining why people ignore it. Some readers will already know that a Compute ...
    Posted to Page Free Space (Weblog) by Paul White on September 4, 2012
  • Deletes that Split Pages and Forwarded Ghosts

    Can DELETE operations cause pages to split?  Yes.  It sounds counter-intuitive on the face of it; deleting rows frees up space on a page, and page splitting occurs when a page needs additional space.  Nevertheless, there are circumstances when deleting rows causes them to expand before they can be deleted.  The mechanism at ...
    Posted to Page Free Space (Weblog) by Paul White on August 30, 2012
  • Two New Slide Decks. Plus, the Week in Colorado.

    I had the honor of traveling the great state of Colorado last week, speaking at the PASS chapters in Boulder, Colorado Springs, and Denver.  At all three events, we had a stellar attendance and, at least in Denver, broke all the records in recent memory both in terms of overall attendance and in first-timers. ...
    Posted to Kevin Kline (Weblog) by KKline on August 20, 2012
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